Interview Questions, ASP.net & C# Code Samples...

master page

2011-10-20T10:44:00.001-07:00

A Nested master page is a master page associated with another master page. To create a nested master page, set the MasterPageFile attribute of the @Master directive to the name of the .master file of the base master page.

Custom Control?

2011-10-20T10:43:00.001-07:00

Custom controls are compiled components that run on the server and that encapsulate user-interface and other related functionality into reusable packages. They can include all the design-time features of standard ASP.NET server controls, including full support for Visual Studio design features such as the Properties window, the visual designer, and the Toolbox.

user and custom controls

2011-10-20T10:35:00.001-07:00

User controls are easier to create in comparison to custom controls, however user controls can be less convenient to use in advanced scenarios.

User controls have limited support for consumers who use a visual design tool whereas custom controls have full visual design tool support for consumers.

A separate copy of the user control is required in each application that uses it whereas only a single copy of the custom control is required, in the global assembly cache, which makes maintenance easier.

A user control cannot be added to the Toolbox in Visual Studio whereas custom controls can be added to the Toolbox in Visual Studio.

User controls are good for static layout whereas custom controls are good for dynamic layout.

Web.config and Machine.config

2011-10-20T10:34:00.000-07:00

Web.config files are used to apply configuration settings to a particular web application whereas machine.config file is used to apply configuration settings for all the websites on a web server.

Web.config files are located in the application's root directory or inside a folder situated in a lower hierarchy. The machine.config is located in the Windows directory Microsoft.Net\Framework\Version\CONFIG.

There can be multiple web.config files in an application nested at different hierarchies. However there can be only one machine.config file on a web server.

inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe

2011-10-20T10:32:00.000-07:00

Describe the role of inetinfo.exe, aspnet_isapi.dll andaspnet_wp.exe in the page loading process.

inetinfo.exe is theMicrosoft IIS server running, handling ASP.NET requests among other things.When an ASP.NET request is received (usually a file with .aspx extension), the ISAPI filter aspnet_isapi.dll takes care of it by passing the request tothe actual worker process aspnet_wp.exe.

typed dataset

2011-09-28T11:45:00.000-07:00

What is typed dataset?

A typed dataset will be having the sehema with them as in an xml format. It raises the compile time exceptions. Arranging data and giving relationship is possible through this.

side-by-side execution

2011-09-28T11:33:00.000-07:00

What is side-by-side execution? Can two application one using private assembly and

other using Shared assembly be stated as a side-by-side executables?

Side-by-side execution is the ability to run multiple versions of an application or component on the same computer. You can have multiple versions of the common language runtime, and multiple versions of applications and components that use a version of the runtime, on the same computer at the same time. Since versioning is only applied to shared assemblies, and not to private assemblies, two application one using private assembly and one using shared assembly cannot be stated as side-by-side executables

Immutable data Type

2011-09-28T11:32:00.000-07:00

Why string is called Immutable data Type?

The memory representation of string is an Array of Characters, So on re-assigning the new array of Char is formed & the start address is changed. Thus keeping the Old string in Memory for Garbage Collector to be disposed.

assembly versioning

2011-09-28T11:31:00.000-07:00

How does assembly versioning work?

Each assembly has a version number called the compatibility version. Also each reference to an assembly (from another assembly) includes both the name and version of the referenced assembly.The version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either of the first two parts different are normally viewed as incompatible. If the first two parts are the same, but the third is different, the assemblies are deemed as 'maybe compatible'. If only the fourth part is different, the assemblies are deemed compatible. However, this is just the default guideline - it is the version policy that decides to what extent these rules are enforced. The version policy can be specified via the application configuration file.

CAS

2011-09-28T11:29:00.000-07:00

How does CAS work?

The CAS security policy revolves around two key concepts - code groups and permissions. Each .NET assembly is a member of a particular code group, and each code group is granted the permissions specified in a named permission set. For example, using the default security policy, a control downloaded from a web site belongs to the 'Zone - Internet' code group, which adheres to the permissions defined by the 'Internet' named permission set. (Naturally the 'Internet' named permission set represents a veryrestrictive range of permissions.)

value-type variables and reference-type

2011-09-28T11:27:00.001-07:00

What is the difference between the value-type variables and reference-type variables in

terms of garbage collection?

The value-type variables are not garbage-collected, they just fall off the stack when they fall

out of scope, the reference-type objects are picked up by GC when their references go null.

StringBuilder over System.String

2011-09-28T11:26:00.002-07:00

What's the advantage of using System.Text.StringBuilder over System.String?

StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text.

Strings are immutable, so each time it's being operated on, a new instance is created.

satellite assembly

2011-09-28T11:26:00.000-07:00

What's a satellite assembly?

When you write a multilingual or multi-cultural application in .NET, and want to distribute

the core application separately from the localized modules, the localized assemblies that

modify the core application are called satellite assemblies.

Thread and a Process?

2011-09-28T11:23:00.000-07:00

Describe the difference between a Thread and a Process?

A Process is an instance of an running application. And a thread is the Execution stream of

the Process. A process can have multiple Thread.

When a process starts a specific memory area is allocated to it. When there is multiple thread

in a process, each thread gets a memory for storing the variables in it and plus they can access

to the global variables which is common for all the thread.

EXE and a DLL?

2011-09-28T11:21:00.001-07:00

What is the difference between an EXE and a DLL?

You can create an object of Dll but not of the EXE.

Dll is an In-Process Component whereas EXE is an OUt-Process Component.

Exe is for single use whereas you can use Dll for multiple use.

Exe can be started as standalone where dll cannot be.

strong-typing versus weak-typing

2011-09-28T11:18:00.000-07:00

What is strong-typing versus weak-typing?

Strong typing implies that the types of variables involved in operations are associated to the variable, checked at compile-time, and require explicit conversion; weak typing implies that they are associated to the value, checked at run-time, and are implicitly converted as required.

Generate a strong name?

2011-09-28T11:17:00.000-07:00

How do you generate a strong name?

.NET provides an utility called strong name tool. You can run this toolfrom the VS.NET command prompt to generate a strong name with an option "-k" and providing the strong key

file name. i.e. sn- -k < file-name >

Debug and Release

2011-09-28T11:16:00.000-07:00

What is the difference between a Debug and Release build?

The Debug build is the program compiled with full symbolic debug information and no optimization. The Release build is the program compiled employing optimization and contains no symbolic debug information. These settings can be changed as per need from Project Configuration properties. The release runs faster since it does not have any debug symbols and is optimized.

Version, Culture and PublicKeyToken

2011-09-28T11:14:00.000-07:00

Explain the importance and use of each, Version, Culture and PublicKeyToken for an assembly.

This three alongwith name of the assembly provide a strong name or fully qualified name to the assembly. When a assebly is referenced with all three.

PublicKeyToken: Each assembly can have a public key embedded in its manifest that identifies the developer. This ensures that once the assembly ships, no one can modify the code or other resources contained in the assembly.

Culture: Specifies which culture the assembly supports

Version: The version number of the assembly.It is of the following form major.minor.build.revision.

Message contract

2011-09-26T03:53:00.001-07:00

Message contract

A message contract describes the format of a message. For example, it declares whether message elements should go in headers versus the body, what level of security should be applied to what elements of the message, and so on.

Operation contract

2011-09-26T03:52:00.001-07:00

Operation contract

An operation contract defines the parameters and return type of an operation. When creating an interface that defines the service contract, you signify an operation contract by applying the OperationContractAttribute attribute to each method definition that is part of the contract. The operations can be modeled as taking a single message and returning a single message, or as taking a set of types and returning a type. In the latter case, the system will determine the format for the messages that need to be exchanged for that operation.

Service contract

2011-09-26T03:51:00.000-07:00

Service contract

The service contract ties together multiple related operations into a single functional unit. The contract can define service-level settings, such as the namespace of the service, a corresponding callback contract, and other such settings. In most cases, the contract is defined by creating an interface in the programming language of your choice and applying the ServiceContractAttribute attribute to the interface. The actual service code results by implementing the interface.

Service operation

2011-09-26T03:50:00.000-07:00

Service operation

A service operation is a procedure defined in a service's code that implements the functionality for an operation. This operation is exposed to clients as methods on a WCF client. The method may return a value, and may take an optional number of arguments, or take no arguments, and return no response. For example, an operation that functions as a simple "Hello" can be used as a notification of a client's presence and to begin a series of operations.

System-provided bindings

2011-09-26T03:48:00.001-07:00

System-provided bindings

WCF includes a number of system-provided bindings. These are collections of binding elements that are optimized for specific scenarios. For example, the WSHttpBinding is designed for interoperability with services that implement various WS-* specifications. These predefined bindings save time by presenting only those options that can be correctly applied to the specific scenario. If a predefined binding does not meet your requirements, you can create your own custom binding.

2011-09-26T03:47:00.005-07:00

Behaviors

A behavior is a component that controls various run-time aspects of a service, an endpoint, a particular operation, or a client. Behaviors are grouped according to scope: common behaviors affect all endpoints globally, service behaviors affect only service-related aspects, endpoint behaviors affect only endpoint-related properties, and operation-level behaviors affect particular operations. For example, one service

behavior is throttling, which specifies how a service reacts when an excess of messages threaten to overwhelm its handling capabilities. An endpoint behavior, on the other hand, controls only aspects relevant to endpoints, such as how and where to find a security credential.

Binding element

2011-09-26T03:47:00.001-07:00

Binding element

A binding element represents a particular piece of the binding, such as a transport, an encoding, an implementation of an infrastructure-level protocol (such as WSReliableMessaging), or any other component of the communication stack.

Binding

2011-09-26T03:46:00.001-07:00

Binding

A binding defines how an endpoint communicates to the world. It is constructed of a set of components called binding elements that "stack" one on top of the other to create the communication infrastructure. At the very least, a binding defines the transport (such as HTTP or TCP) and the encoding being used (such as text or binary). A binding can contain binding elements that specify details like the security mechanisms used to secure messages, or the message pattern used by an endpoint.

Address

2011-09-26T03:45:00.001-07:00

Address

An address specifies the location where messages are received. It is specified as a Uniform Resource Identifier (URI). The URI schema part names the transport mechanism to use to reach the address, such as HTTP and TCP. The hierarchical part of the URI contains a unique location whose format is dependent on the transport mechanism.

The endpoint address enables you to create unique endpoint addresses for each endpoint in a service, or under certain conditions share an address across endpoints. The following example shows an address using the HTTPS protocol with a nondefault port: TPS://cohowinery:8005/ServiceModelSamples/CalculatorService

Infrastructure endpoint

2011-09-26T03:44:00.001-07:00

Infrastructure endpoint

An endpoint that is exposed by the infrastructure to facilitate functionality that is needed or provided by the service that does not relate to a service contract. For example, a service might have an infrastructure endpoint that provides metadata information.

Application endpoint

2011-09-26T03:43:00.002-07:00

Application endpoint

An endpoint exposed by the application and that corresponds to a service contract implemented by the application.

Endpoint

2011-09-26T03:43:00.000-07:00

Endpoint

An endpoint is a construct at which messages are sent or received (or both). It comprises a location (an address) that defines where messages can be sent, a specification of the communication mechanism (a binding) that described how messages should be sent, and a definition for a set of messages that can be sent or received (or both) at that location (a service contract) that describes what message can be sent.

An WCF service is exposed to the world as a collection of endpoints.

Service

2011-09-26T03:42:00.001-07:00

Service

A service is a construct that exposes one or more endpoints, with each endpoint exposing one or more service operations.

Message

2011-09-26T03:41:00.001-07:00

Message

A message is a self-contained unit of data that may consist of several parts, including a body and headers.

Communication Protocols

2011-09-26T03:40:00.000-07:00

Communication Protocols

One required element of the communication stack is the transport protocol. Messages can be sent over intranets and the Internet using common transports, such as HTTP and TCP. Other transports are included that support communication with Microsoft Message Queuing (MSMQ) applications and nodes on a Peer Networking mesh. More transport mechanisms can be added using the built-in extension points of WCF.

Another required element in the communication stack is the encoding that specifies how any

given message is formatted. WCF provides the following encodings:

· Text encoding, an interoperable encoding.
· Message Transmission Optimization Mechanism (MTOM) encoding, which is an interoperable way for efficiently sending unstructured binary data to and from a service.
· Binary encoding for efficient transfer.

More encoding mechanisms (for example, a compression encoding) can be added using the built-in extension points of WCF.

Messaging and Endpoints

2011-09-26T03:38:00.000-07:00

Messaging and Endpoints

WCF is based on the notion of message-based communication, and anything that can be modeled as a message (for example, an HTTP request or an MSMQ message) can be represented in a uniform way in the programming model. This enables a unified API across different transport mechanisms.The model distinguishes between clients, which are applications that initiate communication, and services, which are applications that wait for clients to communicate with them and respond to that communication. A single application can act as both a client and a service. Messages are sent between endpoints. Endpoints are places where messages are sent or received (or both), and they define all the information required for the message exchange. A service exposes one or more application endpoints (as well as zero or more infrastructure endpoints), and the client generates an endpoint that is compatible with one of the service's

endpoints.

An endpoint describes in a standard-based way where messages should be sent, how they should be sent, and what the messages should look like. A service can expose this information as metadata that clients can process to generate appropriate WCF clients and communication stacks.

ASP.NET Caching Features

2011-09-18T23:58:00.000-07:00

ASP.NET Caching Features

One of the most important factors in building high-performance, scalable Web applications is the ability to store items, whether data objects, pages, or parts of a page, in memory the initial time they are requested. You can store these items on the Web server or other software in the request stream, such as the proxy server or browser. This allows you to avoid recreating information that satisfied a previous request, particularly information that demands significant processor time or other resources. Known as caching, it allows you to use a number of techniques to store page output or application data across HTTP requests and reuse it. Thus, the server does not have to recreate information, saving time and resources.

ASP.NET provides two types of caching that you can use to create high-performance Web applications. The first is called output caching, which allows you to store dynamic page and user control responses on any HTTP 1.1 cache-capable device in the output stream, from the originating server to the requesting browser. On subsequent requests, the page or user control code is not executed; the cached output is used to satisfy the request. The second type of caching is traditional application data caching, which you can use to programmatically store arbitrary objects, such as data sets, to server memory so that your application can save the time and resources it takes to recreate them.

Caching ASP.NET Pages

ASP.NET allows you to cache the entire response content for dynamic pages on HTTP 1.1 capable mechanisms, including browsers, proxy servers, and the Web server where your application resides. This provides a powerful way for you to increase the performance of your Web applications. Called output caching, it allows subsequent requests for a particular page to be satisfied from the cache so the code that initially creates the page does not have to be run upon subsequent requests. Using this technique to cache your site's most frequently accessed pages can increase your Web server's throughput, commonly measured in requests per second, substantially.

You have your choice of a high-level declarative API or a low-level programmatic API when manipulating the output cache for a page. You can use the former by including the @ OutputCache directive in the .aspx file for the page. The @ OutputCache directive can meet nearly all the common needs you may have when you want to cache a page's output. The following directive, when included in an .aspx file, sets an expiration of 60 seconds for the cached output of a dynamically generated page.

CAUTION When you use the @ OutputCache directive, the Duration and VaryByParam attributes are required. If you do not include them, a parser error occurs when the page is first requested. If you do not want to use the functionality that the VaryByParam attribute provides, you must set its value to None. For more information about using the VaryByParam attribute, see Caching Multiple Versions of a Page.

ASP.NET also includes a set of APIs that control output-cache expirations and policies for a page programmatically through the HttpCachePolicy class. This class, its methods, and its properties are available through the HttpResponse.Cache property. In turn, you can access this property from the Page object through the Page.Response property.

You can enable or disable page output caching for cache-capable devices in the request stream either declaratively or programmatically as well. In the @ OutputCache directive for a page you can use the Location attribute to specify whether the page's output can be cached on proxy servers, browser clients, the originating Web server, or all or none of these. You can do the same programmatically using the HttpCachePolicy.SetCacheability method to specify the appropriate HttpCacheability enumeration value for your page. For more information, see Setting the Cacheability of a Page.

Responses generated by GET requests with query string parameters or form POST requests with parameters can also be cached, but caching for the passed parameters must be explicitly enabled using the @ OutputCache directive's VaryByParam attribute. For more information, see Caching Multiple Versions of a Page.

Caching Options in ASP.NET

ASP.NET supports three types of caching for Web-based applications:

• Page Level Caching (called Output Caching)

• Page Fragment Caching (often called Partial-Page Output Caching)

• Programmatic or Data Caching

We'll look at each of these options, including how, and when, to use each option to increase your site's performance!

Duplicate Rows

2011-09-18T23:51:00.000-07:00

How does one eliminate duplicates rows from a table?

Choose one of the following queries to identify or remove duplicate rows from a table leaving only unique

records in the table:

Method 1:

DELETE FROM table_name A WHERE ROWID > ( SELECT min(rowid) FROM table_name B WHERE A.key_values = B.key_values);

Method 2:

create table table_name2 as select distinct * from table_name1;

drop table_name1;

rename table_name2 to table_name1;

-- Remember to recreate all indexes, constraints, triggers, etc on table...

Method 3:

delete from my_table t1

where exists (select 'x' from my_table t2

where t2.key_value1 = t1.key_value1

and t2.key_value2 = t1.key_value2

and t2.rowid > t1.rowid);

Note: One can eliminate N^2 unnecessary operations by creating an index on the joined fields in the inner

loop (no need to loop through the entire table on each pass by a record). This will speed-up the deletion

process.

Note 2: If you are comparing NOT-NULL columns, use the NVL function. Remember that NULL is not

equal to NULL. This should not be a problem as all key columns should be NOT NULL by definition.

special characters

2011-09-18T23:48:00.000-07:00

How does one escape special characters when building SQL queries?

The LIKE keyword allows for string searches. The '_' wild card character is used to match exactly one

character, '%' is used to match zero or more occurrences of any characters. These characters can be escaped in SQL. Example:

SELECT name FROM emp WHERE id LIKE '%\_%' ESCAPE '\';

Use two quotes for every one displayed. Example:

SELECT 'Franks''s Oracle site' FROM DUAL;

SELECT 'A ''quoted'' word.' FROM DUAL;

SELECT 'A ''''double quoted'''' word.' FROM DUAL;

DDL, DML and DCL

2011-09-18T23:46:00.000-07:00

What are the difference between DDL, DML and DCL commands?

DDL is Data Definition Language statements. Some examples:

• CREATE - to create objects in the database

• ALTER - alters the structure of the database

• DROP - delete objects from the database

• TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed

• COMMENT - add comments to the data dictionary

• GRANT - gives user's access privileges to database

• REVOKE - withdraw access privileges given with the GRANT command

DML is Data Manipulation Language statements. Some examples:

• SELECT - retrieve data from the a database

• INSERT - insert data into a table

• UPDATE - updates existing data within a table

• DELETE - deletes all records from a table, the space for the records remain

• CALL - call a PL/SQL or Java subprogram

• EXPLAIN PLAN - explain access path to data

• LOCK TABLE - control concurrency

DCL is Data Control Language statements. Some examples:

• COMMIT - save work done

• SAVEPOINT - identify a point in a transaction to which you can later roll back

• ROLLBACK - restore database to original since the last COMMIT

• SET TRANSACTION - Change transaction options like what rollback segment to use

Execution Plan

2011-08-03T11:31:00.001-07:00

What is an execution plan? When would you use it? How would you view the execution plan?

An execution plan is basically a road map that graphically or textually shows the data retrieval methods chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful tool for a developer to understand the performance characteristics of a query or stored procedure since the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or query. From within Query Analyzer is an option called “Show Execution Plan” (located on the Query drop-down menu). If this option is turned on it will display query execution plan in separate window when query is ran again.

XML & SQL

2011-08-03T11:30:00.000-07:00

How do SQL server 2000 and XML linked? Can XML be used to access data?

FOR XML (ROW, AUTO, EXPLICIT)

You can execute SQL queries against existing relational databases to return results as XML rather than standard rowsets. These queries can be executed directly or from within stored procedures. To retrieve XML results, use the FOR XML clause of the SELECT statement and specify an XML mode of RAW, AUTO, or EXPLICIT.

OPENXML

OPENXML is a Transact-SQL keyword that provides a relational/rowset view over an in-memory XML document. OPENXML is a rowset provider similar to a table or a view. OPENXML provides a way to access XML data within the Transact-SQL context by transferring data from an XML document into the relational tables. Thus, OPENXML allows you to manage an XML document and its interaction with the relational environment.

Advantages of Stored Procedure

2011-08-03T11:29:00.000-07:00

Advantages of Stored Procedure.

Stored procedure can reduced network traffic and latency, boosting application performance.
Stored procedure execution plans can be reused, staying cached in SQL Server’s memory, reducing server overhead.
Stored procedures help promote code reuse.
Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.
Stored procedures provide better security to your data.

Self Join & Cross Join?

2011-08-03T11:27:00.001-07:00

What is Self Join?

This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it involves a relationship with only one table. The common example is when company have a hierarchal reporting structure whereby one member of staff reports to another.

What is Cross Join?

A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. The common example is when company wants to combine each product with a pricing table to analyze each product at each price.

Table & Indexes

2011-08-03T11:26:00.000-07:00

What is a table called, if it does not have neither Cluster nor Non-cluster Index? What is it used for?

Unindexed table or Heap. Microsoft Press Books and Book On Line (BOL) refers it as Heap.

A heap is a table that does not have a clustered index and, therefore, the pages are not linked by pointers. The IAM pages are the only structures that link the pages in a table together.

Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table and than do bulk of inserts and to restore those indexes after that.

Identity

2011-08-03T11:25:00.001-07:00

What is Identity?

Identity (or AutoNumber) is a column that automatically generates numeric values. A start and increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers, the value of this cannot be controled. Identity/GUID columns do not need to be indexed.

Error and Rowcount

2011-08-03T11:24:00.002-07:00

How to get @@error and @@rowcount at the same time?

If @@Rowcount is checked after Error checking statement then it will have 0 as the value of @@Recordcount as it would have been reset. And if @@Recordcount is checked before the error-checking statement then @@Error would get reset. To get @@error and @@rowcount at the same time do both in same statement and store them in local variable.

De-normalization

2011-08-03T11:24:00.000-07:00

What is De-normalization?

De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.

Relational tables

2011-08-03T11:23:00.000-07:00

What are the properties of the Relational tables?

Relational tables have six properties:

Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.

2011-08-03T11:22:00.000-07:00

What is data integrity? Explain constraints?

Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.

A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.

A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.

A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.

A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.

A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.

Primary keys and Foreign keys?

2011-08-03T11:21:00.000-07:00

What are primary keys and foreign keys?

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.

Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.

master, msdb, model, tempdb

2011-08-03T11:20:00.001-07:00

What is the basic functions for master, msdb, model, tempdb databases?

The Master database holds information for all databases located on the SQL Server instance and is the glue that holds the engine together. Because SQL Server cannot start without a functioning master database, you must administer this database with care.

The msdb database stores information regarding database backups, SQL Agent information, DTS packages, SQL Server jobs, and some replication information such as for log shipping.

The tempdb holds temporary objects such as global and local temporary tables and stored procedures.

The model is essentially a template database used in the creation of any new user database created in the instance.

Local and a Global Variable

2011-08-03T11:18:00.000-07:00

What is the difference between a local and a global variable?

A local temporary table exists only for the duration of a connection or, if defined inside a compound statement, for the duration of the compound statement.

A global temporary table remains in the database permanently, but the rows exist only within a given connection. When connection are closed, the data in the global temporary table disappears. However, the table definition remains with the database for access when database is opened next time.

Log shipping

2011-08-03T11:17:00.001-07:00

What is log shipping?

Log shipping is the process of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a standby server. Enterprise Editions only supports log shipping. In log shipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db can be used this as the Disaster Recovery plan. The key feature of log shipping is that is will automatically backup transaction logs throughout the day and automatically restore them on the standby server at defined interval.

ERROR && Raiseerror

2011-08-03T11:16:00.001-07:00

What is @@ERROR?

The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement, it must be saved to a variable if it is needed to process it further after checking it.

What is Raiseerror?

Stored procedures report errors to client applications via the RAISERROR command. RAISERROR doesn’t change the flow of a procedure; it merely displays an error message, sets the @@ERROR automatic variable, and optionally writes the message to the SQL Server error log and the NT application event log.

Recursive stored procedure

2011-08-03T11:15:00.001-07:00

Can a stored procedure call itself or recursive stored procedure? How many level SP nesting possible?

Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves. Recursion can be defined as a method of problem solving wherein the solution is arrived at by repetitively applying it to subsets of the problem. A common application of recursive logic is to perform numeric computations that lend themselves to repetitive evaluation by the same processing steps. Stored procedures are nested when one stored procedure calls another or executes managed code by referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code references up to 32 levels.

SQL server agent

2011-08-03T11:14:00.001-07:00

What is SQL server agent?

SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to schedule your own jobs and scripts.

Authentication Modes

2011-08-03T11:13:00.001-07:00

What are the authentication modes in SQL Server? How can it be changed?

Windows mode and mixed mode (SQL & Windows).

To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group. Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the Security page.

User -Defined functions

2011-08-03T11:12:00.000-07:00

What is User Defined Functions?

User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters and return a single scalar data value or a table data type.

What kind of User-Defined Functions can be created?

There are three types of User-Defined functions in SQL Server 2000 and they are Scalar, Inline Table-Valued and Multi-statement Table-valued.

Scalar User-Defined Function

A Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp data types are not supported. These are the type of user-defined functions that most developers are used to in other programming languages. You pass in 0 to many parameters and you get a return value.

Inline Table-Value User-Defined Function

An Inline Table-Value user-defined function returns a table data type and is an exceptional alternative to a view as the user-defined function can pass parameters into a T-SQL select command and in essence provide us with a parameterized, non-updateable view of the underlying tables.

Multi-statement Table-Value User-Defined Function

A Multi-Statement Table-Value user-defined function returns a table and is also an exceptional alternative to a view as the function can support multiple T-SQL statements to build the final result where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a T-SQL select command or a group of them gives us the capability to in essence create a parameterized, non-updateable view of the data in the underlying tables. Within the create function command you must define the table structure that is being returned. After creating this type of user-defined function, It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored procedure which can also return record sets.

SQL Profiler

2011-08-03T11:08:00.001-07:00

What is SQL Profiler?

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to analyze later. For example, you can monitor a production environment to see which stored procedures are hampering performance by executing too slowly.

Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too large, you can filter them based on the information you want, so that only a subset of the event data is collected. Monitoring too many events adds overhead to the server and the monitoring process and can cause the trace file or trace table to grow very large, especially when the monitoring process takes place over a long period of time.

Sub-query

2011-08-03T11:05:00.001-07:00

What is sub-query? Explain properties of sub-query.

Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of parentheses. Sub-queries are generally used to return a single row as an atomic value, though they may be used to compare values against multiple rows with the IN keyword.

A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT statement if executed independently of the T-SQL statement, in which it is nested, will return a result set. Meaning a subquery SELECT statement can standalone and is not depended on the statement in which it is nested. A subquery SELECT statement can return any number of values, and can be found in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery can be used anywhere an expression can be used.

Properties of Sub-Query

A subquery must be enclosed in the parenthesis.

A subquery must be put in the right hand of the comparison operator, and

A subquery cannot contain a ORDER-BY clause.

A query can contain more than one sub-queries.

What are types of sub-queries?

Single-row subquery, where the subquery returns only one row.

Multiple-row subquery, where the subquery returns multiple rows,.and

Multiple column subquery, where the subquery returns multiple columns.

HAVING & WHERE CLAUSE?

2011-08-03T11:04:00.001-07:00

What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. HAVING criteria is applied after the the grouping of rows has occurred.

Function and Stored Procedure

2011-08-03T11:03:00.002-07:00

Difference between Function and Stored Procedure?

UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as Stored procedures cannot be.

UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables.

Inline UDF’s can be though of as views that take parameters and can be used in JOINs and other Rowset operations.

DELETE & TRUNCATE

2011-08-03T11:03:00.000-07:00

What is difference between DELETE & TRUNCATE commands?

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.

TRUNCATE

TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.

TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the page deallocations are recorded in the transaction log.

TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes and so on remain. The counter used by an identity for new rows is reset to the seed for the column.

You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint. Because TRUNCATE TABLE is not logged, it cannot activate a trigger.

TRUNCATE can not be Rolled back using logs.

TRUNCATE is DDL Command.

TRUNCATE Resets identity of the table.

DELETE

DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.

If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.

DELETE Can be used with or without a WHERE clause

DELETE Activates Triggers.

DELETE Can be Rolled back using logs.

DELETE is DML Command.

DELETE does not reset identity of the table.

NOLOCK

2011-08-03T11:01:00.000-07:00

What is a NOLOCK?

Using the NOLOCK query optimiser hint is generally considered good practice in order to improve concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are taken when data is read. The result is a Dirty Read, which means that another process could be updating the data at the exact time you are reading it. There are no guarantees that your query will retrieve the most recent data. The advantage to performance is that your reading of data will not block updates from taking place, and updates will not block your reading of data. SELECT statements take Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but other processes are blocked from modifying the data. The updates will queue until all the reads have completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay(blocking).

Relationships

2011-08-03T10:52:00.000-07:00

How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary and foreign key relationships.

One-to-Many relationships are implemented by splitting the data into two tables with primary key and foreign key relationships.

Many-to-Many relationships are implemented using a junction table with the keys from both the tables forming the composite primary key of the junction table.

Primary key and a unique Key

2011-08-03T10:51:00.000-07:00

What’s the difference between a primary key and a unique key?

Both primary key and unique enforce uniqueness of the column on which they are defined. But by default primary key creates a clustered index on the column, where are unique creates a nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.

Collation

2011-08-03T10:49:00.001-07:00

What is Collation?

Collation refers to a set of rules that determine how data is sorted and compared. Character data is sorted using rules that define the correct character sequence, with options for specifying case-sensitivity, accent marks, kana character types and character width.

Cursors

2011-08-03T10:48:00.000-07:00

What is cursors?

Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis, instead of the typical SQL commands that operate on all the rows in the set at one time.

In order to work with a cursor we need to perform some steps in the following order:

Declare cursor
Open cursor
Fetch row from the cursor
Process fetched row
Close cursor
Deallocate cursor

Index Configurations

2011-08-03T10:47:00.000-07:00

What are the different index configurations a table can have?

A table can have one of the following index configurations:

No indexes
A clustered index
A clustered index and many nonclustered indexes
A nonclustered index
Many nonclustered indexes

Clustered and a Non-Clustered index

2011-08-03T10:45:00.001-07:00

What is the difference between clustered and a non-clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.

A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.

RDBMS

2011-08-03T10:44:00.001-07:00

What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage.

Normalization Forms

2011-08-03T10:43:00.000-07:00

What are different normalization forms?

1NF: Eliminate Repeating Groups

Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.

2NF: Eliminate Redundant Data

If an attribute depends on only part of a multi-valued key, remove it to a separate table.

3NF: Eliminate Columns Not Dependent On Key

If attributes do not contribute to a description of the key, remove them to a separate table. All attributes must be directly dependent on the primary key

BCNF: Boyce-Codd Normal Form

If there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.

4NF: Isolate Independent Multiple Relationships

No table may contain two or more 1:n or n:m relationships that are not directly related.

5NF: Isolate Semantically Related Multiple Relationships

There may be practical constrains on information that justify separating logically related many-to-many relationships.

ONF: Optimal Normal Form

A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.

DKNF: Domain-Key Normal Form

A model free from all modification anomalies.

Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.

Stored Procedure

2011-08-03T10:41:00.001-07:00

What is Stored Procedure?

A stored procedure is a named group of SQL statements that have been previously created and stored in the server database. Stored procedures accept input parameters so that a single procedure can be used over the network by several clients using different input data. And when the procedure is modified, all clients automatically get the new version. Stored procedures reduce network traffic and improve performance. Stored procedures can be used to help ensure the integrity of the database.

Index

2011-08-03T10:40:00.001-07:00

What is Index?

An index is a physical structure containing pointers to the data. Indices are created in an existing table to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of a table, and each index is given a name. The users cannot see the indexes, they are just used to speed up queries. Effective indexes are one of the best ways to improve performance in a database application. A table scan happens when there is no index available to help a query. In a table scan SQL Server examines every row in the table to satisfy the query results. Table scans are sometimes unavoidable, but on large tables, scans have a terrific impact on performance.

Clustered indexes define the physical sorting of a database table’s rows in the storage media. For this reason, each database table may have only one clustered index.

Non-clustered indexes are created outside of the database table and contain a sorted list of references to the table itself.

View

2011-08-03T10:39:00.001-07:00

What is View?

A simple view can be thought of as a subset of a table. It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted in the table the view was created with. It should also be noted that as data in the original table changes, so does data in the view, as views are the way to look at part of the original table. The results of using a view are not permanently stored in the database. The data accessed through a view is actually constructed using standard T-SQL select command and can come from one to many different base tables or even other views.

Trigger

2011-08-03T10:37:00.000-07:00

What is Trigger?

A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.

Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.

Data Contract

2011-08-03T10:26:00.000-07:00

Data Contract

A data contract is a formal agreement between a service and a client that abstractly describes the data to be exchanged.

Data contract can be explicit or implicit. Simple type such as int, string etc has an implicit data contract. User defined object are explicit or Complex type, for which you have to define a Data contract using [DataContract] and [DataMember] attribute.

A data contract can be defined as follows:

It describes the external format of data passed to and from service operations

It defines the structure and types of data exchanged in service messages

It maps a CLR type to an XML Schema

t defines how data types are serialized and deserialized. Through serialization, you convert an object into a sequence of bytes that can be transmitted over a network. Through deserialization, you reassemble an object from a sequence of bytes that you receive from a calling application.

It is a versioning system that allows you to manage changes to structured data

We need to include System.Runtime.Serialization reference to the project. This assembly holds the DataContract and DataMember attribute.

Create user defined data type called Employee. This data type should be identified for serialization and deserialization by mentioning with [DataContract] and [DataMember] attribute.

[ServiceContract]

    public interface IEmployeeService

    {

        [OperationContract]

        Employee GetEmployeeDetails(int EmpId);

    }



    [DataContract]

    public class Employee

    {

        private string m_Name;

        private int m_Age;

        private int m_Salary;

        private string m_Designation;

        private string m_Manager;



        [DataMember]

        public string Name

        {

            get { return m_Name; }

            set { m_Name = value; }

        }



        [DataMember]

        public int Age

        {

            get { return m_Age; }

            set { m_Age = value; }

        }



        [DataMember]

        public int Salary

        {

            get { return m_Salary; }

            set { m_Salary = value; }

        }



        [DataMember]

        public string Designation

        {

            get { return m_Designation; }

            set { m_Designation = value; }

        }



        [DataMember]

        public string Manager

        {

            get { return m_Manager; }

            set { m_Manager = value; }

        }



    }

Implementation of the service class is shown below. In GetEmployee method we have created the Employee instance and return to the client. Since we have created the data contract for the Employee class, client will aware of this instance whenever he creates proxy for the service.

public class EmployeeService : IEmployeeService

    {

        public Employee GetEmployeeDetails(int empId)

        {

            

            Employee empDetail = new Employee();



            //Do something to get employee details and assign to 'empDetail' properties



            return empDetail;

        }

    }

Client side

On client side we can create the proxy for the service and make use of it. The client side code is shown below.

protected void btnGetDetails_Click(object sender, EventArgs e)

{

EmployeeServiceClient objEmployeeClient = new EmployeeServiceClient();



Employee empDetails;



empDetails = objEmployeeClient.GetEmployeeDetails(empId);



//Do something on employee details

}

Extension Methods

2011-08-03T09:43:00.000-07:00

Another cool feature of C# 3.0 is Extension Methods. They allow you to extend an existing type with new functionality, without having to sub-class or recompile the old type. For instance, you might like to know whether a certain string was a number or not. The usual approach would be to define a function and then call it each time, and once you got a whole lot of those kind of functions, you would put them together in a utility class, like this:

public class MyUtils

{

public static bool IsNumeric(string s)

{

float output;

return float.TryParse(s, out output);

}

}

Now you could check a string by executing a line of code like this:

string test = "4";

if (MyUtils.IsNumeric(test))

console.WriteLine("Yes");

else

console.WriteLine("No");

However, with Extension Methods, you can actually extend the String class to support this directly. You do it by defining a static class, with a set of static methods that will be your library of extension methods. Here is an example:

public static class MyExtensionMethods

{

public static bool IsNumeric(this string s)

{

float output;

return float.TryParse(s, out output);

}

}

The only thing that separates this from any other static method, is the "this" keyword in the parameter section of the method. It tells the compiler that this is an extension method for the string class, and that's actually all you need to create an extension method. Now, you can call the IsNumeric() method directly on strings, like this:

string test = "4";

if (test.IsNumeric())

console.WriteLine("Yes");

else

Console.WriteLine("No");

WCF Concurrency

2011-08-03T09:15:00.000-07:00

What are 3 ways of implementing WCF concurrency?

Single: - A single request has access to the WCF service object at a given moment of time. So only one request will be processed at any given moment of time. The other requests have to wait until the request processed by the WCF service is not completed.

Multiple: - In this scenario multiple requests can be handled by the WCF service object at any given moment of time. In other words request are processed at the same time by spawning multiple threads on the WCFserver object. So you have great a throughput here but you need to ensure concurrency issues related to WCF server objects.

Reentrant: - A single request thread has access to the WCF service object, but the thread can exit the WCF service to call another WCF service or can also call WCF client through callback and reenter without deadlock.

Finalize and Dispose

2011-08-02T11:35:00.000-07:00

What is the difference between Finalize and Dispose (Garbage collection)

Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object.

In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object. Dispose can be called even if other references to the object are alive.

Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose.

Private Constructor

2011-08-02T11:34:00.001-07:00

What is Private Constructor? and it’s use? Can you create instance of a class which has Private Constructor?

A: When a class declares only private instance constructors, it is not possible for classes outside the program to derive from the class or to directly create instances of it. (Except Nested classes)

Make a constructor private if:

- You want it to be available only to the class itself. For example, you might have a special constructor used only in the implementation of your class' Clone method.

- You do not want instances of your component to be created. For example, you may have a class containing nothing but Shared utility functions, and no instance data. Creating instances of the class would waste memory.

Scenario for Interface or Abstract Class

2011-08-02T11:33:00.000-07:00

In which Scenario you will go for Interface or Abstract Class?

Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes. Even though class inheritance allows your classes to inherit implementation from a base class, it also forces you to make most of your design decisions when the class is first published.

Abstract classes are useful when creating components because they allow you specify an invariant level of functionality in some methods, but leave the implementation of other methods until a specific implementation of that class is needed. They also version well, because if additional functionality is needed in derived classes, it can be added to the base class without breaking code. Interfaces vs. Abstract Classes

Multiple inheritance

A class may implement several interfaces.
A class may extend only one abstract class.

Default implementation

An interface cannot provide any code at all, much less default code.
An abstract class can provide complete code, default code, and/or just stubs that have to be overridden.

Constants

Static final constants only, can use them without qualification in classes that implement the interface. On the other paw, these unqualified names pollute the namespace. You can use them and it is not obvious where they are coming from since the qualification is optional.
Both instance and static constants are possible. Both static and instance intialiser code are also possible to compute the constants.

Third party convenience

An interface implementation may be added to any existing third party class.
A third party class must be rewritten to extend only from the abstract class.

is-a vs -able or can-do

Interfaces are often used to describe the peripheral abilities of a class, not its central identity, e.g. an Automobile class might implement the Recyclable interface, which could apply to many otherwise totally unrelated objects.
An abstract class defines the core identity of its descendants. If you defined a Dog abstract class then Damamation descendants are Dogs, they are not merely dogable. Implemented interfaces enumerate the general things a class can do, not the things a class is.

Plug-in

You can write a new replacement module for an interface that contains not one stick of code in common with the existing implementations. When you implement the interface, you start from scratch without any default implementation. You have to obtain your tools from other classes; nothing comes with the interface other than a few constants. This gives you freedom to implement a radically different internal design.
You must use the abstract class as-is for the code base, with all its attendant baggage, good or bad. The abstract class author has imposed structure on you. Depending on the cleverness of the author of the abstract class, this may be good or bad. Another issue that's important is what I call "heterogeneous vs. homogeneous." If implementors/subclasses are homogeneous, tend towards an abstract base class. If they are heterogeneous, use an interface. (Now all I have to do is come up with a good definition of hetero/homogeneous in this context.) If the various objects are all of-a-kind, and share a common state and behavior, then tend towards a common base class. If all they share is a set of method signatures, then tend towards an interface.

Homogeneity

If all the various implementations share is the method signatures, then an interface works best.
If the various implementations are all of a kind and share a common status and behavior, usually an abstract class works best.

Maintenance

If your client code talks only in terms of an interface, you can easily change the concrete implementation behind it, using a factory method.
Just like an interface, if your client code talks only in terms of an abstract class, you can easily change the concrete implementation behind it, using a factory method.

Speed

Slow, requires extra indirection to find the corresponding method in the actual class. Modern JVMs are discovering ways to reduce this speed penalty.
Fast

Terseness

The constant declarations in an interface are all presumed public static final, so you may leave that part out. You can't call any methods to compute the initial values of your constants. You need not declare individual methods of an interface abstract. They are all presumed so.
You can put shared code into an abstract class, where you cannot into an interface. If interfaces want to share code, you will have to write other bubblegum to arrange that. You may use methods to compute the initial values of your constants and variables, both instance and static. You must declare all the individual methods of an abstract class abstract.

Adding functionality

If you add a new method to an interface, you must track down all implementations of that interface in the universe and provide them with a concrete implementation of that method.
If you add a new method to an abstract class, you have the option of providing a default implementation of it. Then all existing code will continue to work without change.

Struct and a Class

2011-08-02T11:31:00.001-07:00

What is the difference between a Struct and a Class?

The struct type is suitable for representing lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class, a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will allocate additional memory for referencing each object. In this case, the struct is less expensive.
When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized.
It is an error to declare a default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct members to their default values.
It is an error to initialize an instance field in a struct.
There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can implement interfaces, and it does that exactly as classes do.
A struct is a value type, while a class is a reference type.

Namespaces

2011-08-02T11:30:00.000-07:00

What are Namespaces?

The namespace keyword is used to declare a scope. This namespace scope lets you organize code and gives you a way to create globally-unique types. Even if you do not explicitly declare one, a default namespace is created. This unnamed namespace, sometimes called the global namespace, is present in every file. Any identifier in the global namespace is available for use in a named namespace. Namespaces implicitly have public access and this is not modifiable.

Garbage Collector

2011-08-02T11:28:00.001-07:00

How Garbage Collector (GC) Works?

The methods in this class influence when an object is garbage collected and when resources allocated by an object are released. Properties in this class provide information about the total amount of memory available in the system and the age category, or generation, of memory allocated to an object. Periodically, the garbage collector performs garbage collection to reclaim memory allocated to objects for which there are no valid references. Garbage collection happens automatically when a request for memory cannot be satisfied using available free memory. Alternatively, an application can force garbage collection using the Collect method.

Garbage collection consists of the following steps: 0.The garbage collector searches for managed objects that are referenced in managed code. 1.The garbage collector attempts to finalize objects that are not referenced. 2.The garbage collector frees objects that are not referenced and reclaims their memory.

Syntax rules in XML

2011-08-02T11:23:00.000-07:00

Define Syntax rules in XML in brief?

1. All XML Elements Must Have a Closing Tag

2. XML Tags are Case Sensitive

3. XML Elements Must be Properly Nested

4. XML Documents Must Have a Root Element

5. XML Attribute Values Must be Quoted

6. Entity References:

< < less than

> > greater than

& & ampersand

' ' apostrophe " "

7. Comments in XML

8. White-space is Preserved in XML

SOAP and XML

2011-08-02T11:21:00.001-07:00

What is SOAP and how does it relate to XML?

The Simple Object Access Protocol (SOAP) uses XML to define a protocol for the exchange of information in distributed computing environments. SOAP consists of three components: an envelope, a set of encoding rules, and a convention for representing remote procedure calls. Unless experience with SOAP is a direct requirement for the open position, knowing the specifics of the protocol, or how it can be used in conjunction with HTTP, is not as important as identifying it as a natural application of XML.

Protocols behind XML

2011-08-02T11:20:00.000-07:00

What are the core protocols behind XML Web services?

XML (for message format), HTTP and others (for transport), WSDL (Web Service Definition Language, to describe the Web services and define the contract), and UDDI (Universal Description, Discovery and Integration, to dynamically discover and invoke Web services)

W3C

2011-08-02T11:19:00.001-07:00

What is W3C?

World Wide Web Consortium, which defines all the standards for XML and HTML.

LINQ

2011-08-01T23:21:00.000-07:00

What is LINQ?

Language-Integrated Query (LINQ) is a query syntax that defines a set of query operators that enable traversal, filter, and projection operations to be expressed in a declarative way in any .NET-based programming language. The data object can be an in-memory data collection or an object that represents data from a database. You can retrieve or modify the data without having to write SQL commands for each operation.

Example: var col = from o in Orders where o.CustomerID == 84 select o;

Application domain

2011-08-01T23:19:00.002-07:00

What is an application domain?

An application domain (often AppDomain) is a virtual process that serves to isolate an application. All objects created within the same application scope (in other words, anywhere along the sequence of object activations beginning with the application entry point) are created within the same application domain. Multiple application domains can exist in a single operating system process, making them a lightweight means of application isolation

Private and Shared Assemblies

2011-08-01T23:19:00.000-07:00

What are private assemblies and shared assemblies?

A private assembly is used only by a single application, and is stored in that application's install directory (or a subdirectory therein). A shared assembly is one that can be referenced by more than one application. In order to share an assembly, the assembly must be explicitly built for this purpose by giving it a cryptographically strong name (referred to as a strong name). By contrast, a private assembly name need only be unique within the application that uses it.

Meta Data

2011-08-01T23:18:00.000-07:00

What is Meta Data?

Metadata is binary information describing your program that is stored either in a common language runtime portable executable (PE) file or in memory. When you compile your code into a PE file, metadata is inserted into one portion of the file, while your code is converted to Microsoft intermediate language (MSIL) and inserted into another portion of the file. Every type and member defined and referenced in a module or assembly is described within metadata. When code is executed, the runtime loads metadata into memory and references it to discover information about your code's classes, members, inheritance, and so on.

Metadata describes every type and member defined in your code in a language-neutral manner. Metadata stores the following information:

• Description of the assembly.

• Identity (name, version, culture, public key).

• The types that are exported.

• Other assemblies that this assembly depends on.

• Security permissions needed to run.

• Description of types.

• Name, visibility, base class, and interfaces implemented.

• Members (methods, fields, properties, events, nested types).

• Attributes.

• Additional descriptive elements that modify types and members.

Forms Authentication

2011-08-01T23:17:00.003-07:00

What is FormsAuthentication?

Forms authentication uses an authentication ticket that is created when a user logs on to a site, and then it tracks the user throughout the site. The forms authentication ticket is usually contained inside a cookie. However, ASP.NET version 2.0 supports cookie less forms authentication, which results in the ticket being passed in a query string.

If the user requests a page that requires authenticated access and that user has not previously logged on to the site, then the user is redirected to a configured logon page. The logon page prompts the user to supply credentials, typically a user name and password. These credentials are then passed to the server and validated against a user store, such as a SQL Server database. In ASP.NET 2.0, user-store access can be handled by a membership provider. After the user's credentials are authenticated, the user is redirected to the originally requested page. Forms authentication processing is handled by the FormsAuthenticationModule class, which is an HTTP module that participates in the regular ASP.NET page-processing cycle. This document explains how forms authentication works in ASP.NET 2.0.

Bubble Event

2011-08-01T23:16:00.003-07:00

What is Bubble Event?

The ASP.NET page framework provides a technique called event bubbling that allows a child control to propagate events up its containment hierarchy. Event bubbling enables events to be raised from a more convenient location in the controls hierarchy and allows event handlers to be attached to the original control as well as to the control that exposes the bubbled event.

Event bubbling is used by the data-bound controls (Repeater, DataList, and DataGrid) to expose command events raised by child controls (within item templates) as top-level events.

Session Modes

2011-08-01T23:16:00.001-07:00

Explain about types of Session Modes in ASP.NET?

ASP.NET supports three modes of session state:

• InProc: In-Proc mode stores values in the memory of the ASP.NET worker process. Thus, this mode offers the fastest access to these values. However, when the ASP.NET worker process recycles, the state data is lost.

• StateServer: Alternately, StateServer mode uses a stand-alone Microsoft Windows service to store session variables. Because this service is independent of Microsoft Internet Information Server (IIS), it can run on a separate server. You can use this mode for a load-balancing solution because multiple Web servers can share session variables. Although session variables are not lost if you restart IIS, performance is impacted when you cross process boundaries.

• SqlServer: If you are greatly concerned about the persistence of session information, you can use SqlServer mode to leverage Microsoft SQL Server to ensure the highest level of reliability. SqlServer mode is similar to out-of-process mode, except that the session data is maintained in a SQL Server. SqlServer mode also enables you to utilize a state store that is located out of the IIS process and that can be located on the local computer or a remote server.

Hidden Field

2011-08-01T23:15:00.001-07:00

What is Hidden Field?

ASP.NET allows you to store information in a HiddenField control, which renders as a standard HTML hidden field. A hidden field does not render visibly in the browser, but you can set its properties just as you can with a standard control. When a page is submitted to the server, the content of a hidden field is sent in the HTTP form collection along with the values of other controls. A hidden field acts as a repository for any page-specific information that you want to store directly in the page. A HiddenField control stores a single variable in its Value property and must be explicitly added to the page.

Transfer vs Response

2011-08-01T23:10:00.001-07:00

Difference between Server.Transfer vs Response.Redirect?

Server transfer:

• Transfers control to a new page that renders in place of the source page.

• Redirects only to target pages that are in the same Web application as the source page.

• Enables you to read values and public properties from source page.

• Does not update browser information with information about the target page. Pressing the refresh or back buttons in the browser can result in unexpected behavior.

Response.Redirect:

• Performs a new HTTP GET request on the target page.

• Passes the query string (if any) to the target page. In Internet Explorer, the size of the query string is limited to 2,048 characters.

• Provides programmatic and dynamic control over the target URL and query string.

• Enables you to redirect to any page, not just pages in the same Web application.

• Enables you to share information between source and target pages using session state.

Session State

2011-08-01T23:08:00.007-07:00

What is Session State in ASP.NET?

Session State:

You can store values that need to be persisted for the duration of a user's session in session variables. These variables are unique to each user session and can be accessed in any ASP.NET page within an application. You can set and access session information from within an ASP.NET application.

Application State

2011-08-01T23:08:00.003-07:00

What is Application State in ASP.NET?

Application State:

Application state variables are, in effect, global variables for each ASP.NET application. You can share values of these variables throughout that application. These variables are usually set in the Application_OnStart event and then accessed and modified in individual ASP.NET pages.