Friday, August 27, 2010

What is reflection?

All .NET assemblies have metadata information stored about the types defined in modules. This metadata information can be accessed by mechanism called as “Reflection”.System. Reflection can be used to browse through the metadata information.

Using reflection you can also dynamically invoke methods using System.Type.Invokemember. Below is sample source code if needed you can also get this code from CD provided, go to “Source code” folder in “Reflection Sample” folder.

Public Class Form1
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Dim Pobjtype As Type
Dim PobjObject As Object
Dim PobjButtons As New Windows.Forms.Button()
Pobjtype = PobjButtons.GetType()
For Each PobjObject In Pobjtype.GetMembers
LstDisplay.Items.Add(PobjObject.ToString())
Next
End Sub
End Class

Sample source code uses reflection to browse through “Button” class of “Windows.Forms”. If you compile and run the program following is output as shown in “Sample Reflection Display”. Using reflection you can also dynamically invoke a method using “System.Type.InvokeMember”.

Note :- System.Type.InvokeMember is left as homework for readers. Believe me you will enjoy doing it yourself and the concept of reflection will be clearer.

Can we force garbage collector to run ?

System.GC.Collect() forces garbage collector to run. This is not recommended but can be used if situations arises.

What is garbage collection?

Garbage collection is a CLR feature which automatically manages memory. Programmers forget to release the objects while coding ..... Laziness (Remember in VB6 where one of the good practices is to set object to nothing). CLR automatically releases objects when they are no longer in use and refernced. CLR runs on non-deterministic to see the unused objects and cleans them. One side effect of this non-deterministic feature is that we cannot assume an object is destroyed when it goes out of the scope of a function. Therefore, we should not put code into a class destructor to release resources.

What is Delay signing?

During development process you will need strong name keys to be exposed to developer which

is not a good practice from security aspect point of view.In such situations you can assign the key

later on and during development you an use delay signing

Following is process to delay sign an assembly:

  • First obtain your string name keys using SN.EXE.
  • Annotate the source code for the assembly with two custom attributes from System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file containing the public key as a parameter to its constructor. AssemblyDelaySignAttribute, which indicates that delay signing, is being used by passing true as a parameter to its constructor. For example as shown below: [Visual Basic]<Assembly:AssemblyKeyFileAttribute("myKey.snk")> <Assembly:AssemblyDelaySignAttribute(true)> [C#] [assembly:AssemblyKeyFileAttribute("myKey.snk")] [assembly:AssemblyDelaySignAttribute(true)] The compiler inserts the public key into the assembly manifest and reserves space in the PE file for the full strong name signature. The real public key must be stored while the assembly is built so that other assemblies that reference this assembly can obtain the key to store in their own assembly reference.
  • Because the assembly does not have a valid strong name signature, the verification of that signature must be turned off. You can do this by using the –Vr option with theStrong Name tool.The following example turns off verification for an assembly called myAssembly.dll. Sn –Vr myAssembly.dllDLL name of the project.
  • Just before shipping, you submit the assembly to your organization's signing authority for the actual strong name signing using the –R option with the Strong Name tool. The following example signs an assembly called myAssembly.dll with a strong name using the sgKey.snk key pair. Sn -R myAssembly.dll sgKey.snk

How to add and remove an assembly from GAC?

There are two ways to install .NET assembly in GAC:-

  • Using Microsoft Installer Package. You can get download of installer from
  • http://www.microsoft.com/.
  • Using Gacutil. Goto “Visual Studio Command Prompt” and type “gacutil –i (assembly_name)”, where (assembly_name) is the DLL name of the project.

What is GAC ?

Twist :- What are situations when you register .NET assembly in GAC ?

GAC (Global Assembly Cache) is used where shared .NET assembly reside. GAC is used in the

following situations :-

  • If the application has to be shared among several application.
  • If the assembly has some special security requirements like only administratorscan remove the assembly. If the assembly is private then a simple delete of assembly the assembly file will remove the assembly.

Note :- Registering .NET assembly in GAC can lead to the old problem of DLL hell, where COM version was stored in central registry. So GAC should be used when absolutely necessary.

Is versioning applicable to private assemblies?

Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in their individual folders.

Where is version information stored of an assembly?

Version information is stored in assembly in manifest.

What is Manifest

Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the following things (See Figure Manifest View for more details):

  • Version of assembly
  • Security identity
  • Scope of the assembly
  • Resolve references to resources and classes.
  • The assembly manifest can be stored in either a PE file (an .exe or .dll) with Microsoft intermediate language (MSIL) code or in a stand-alone PE file that contains only assembly manifest information.

What is Difference between NameSpace and Assembly

Following are the differences between namespace and assembly :

  • Assembly is physical grouping of logical units. Namespace logically groups classes.
  • Namespace can span multiple assembly.

What is NameSpace

Namespace has two basic functionality :-

  • NameSpace Logically group types, example System.Web.UI logically groups our UI related features.
  • In Object Oriented world many times its possible that programmers will use the same class name.By qualifying NameSpace with classname this collision is able to be removed.

What are the different types of Assembly

There are two types of assembly Private and Public assembly. A private assembly is normally used by a single application, and is stored in the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code which many applications will find useful, e.g. Crystal report classes which will be used by all application for Reports.

What is a Assembly

  • Assembly is unit of deployment like EXE or a DLL.
  • An assembly consists of one or more files (dlls, exe’s, html files etc.), and represents a group of resources, type definitions, and implementations of those types. An assembly may also contain references to other assemblies. These resources, types and references are described in a block of data called a manifest. The manifest is part of the assembly, thus making the assembly self-describing.
  • An assembly is completely self-describing.An assembly contains metadata information, which is used by the CLR for everything from type checking and security to actually invoking the components methods. As all information is in the assembly itself, it is independent of registry. This is the basic advantage as compared to COM where the version was stored in registry.
  • Multiple versions can be deployed side by side in different folders. These different versions can execute at the same time without interfering with each other. Assemblies can be private or shared. For private assembly deployment, the assembly is copied to the same directory as the client program that references it. No registration is needed, and no fancy installation program is required.When the component is removed, no registry cleanup is needed, and no uninstall program is required. Just delete it from the hard drive.
  • In shared assembly deployment, an assembly is installed in the Global Assembly Cache (or GAC). The GAC contains shared assemblies that are globally accessible to all .NET applications on the machine.

What is a Managed Code

Managed code runs inside the environment of CLR i.e. .NET runtime. In short all IL are managed code. But if you are using some third party software example VB6 or VC++ component they are unmanaged code as .NET runtime (CLR) does not have control over the source code execution of the language.in a seamless manner.

What is a CLS(Common Language Specification)

This is a subset of the CTS which all .NET languages are expected to support. It was always a dream of Microsoft to unite all different languages in to one umbrella and CLS is one step towards that. Microsoft has defined CLS which are nothing but guidelines that language to follow so that it can communicate with other .NET languages in a seamless manner.

What is a CTS

In order that two language communicate smoothly CLR has CTS (Common Type System).Example in VB you have “Integer” and in C++ you have “long” these datatypes are not compatible so the interfacing between them is very complicated. In order to able that two different languages can communicate Microsoft introduced Common Type System. So “Integer” datatype in VB6 and “int” datatype in C++ will convert it to System.int32 which is datatype of CTS. CLS which is covered in the coming question is subset of CTS.

Note: If you have undergone COM programming period interfacing VB6 application with VC++ application was a real pain as the datatype of both languages did not have a common ground where they can come and interface, by having CTS interfacing is smooth.

What is a CLR

Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework. All Languages have runtime and its the responsibility of the runtime to take care of the code execution of the program. For example VC++ has MSCRT40.DLL,VB6 has MSVBVM60.DLL, Java has Java Virtual Machine etc. Similarly .NET has CLR. Following are the responsibilities of CLR

  •  Garbage Collection :- CLR automatically manages memory thus eliminating memory leaks. When objects are not referred GC automatically releases those memories thus providing efficient memory management.
  • Code Access Security :- CAS grants rights to program depending on the security configuration of the machine. Example the program has rights to edit or create a new file but the security configuration of machine does not allow the program to delete a file. CAS will take care that the code runs under the environment of machines security configuration.
  • Code Verification :- This ensures proper code execution and type safety while the code runs. It prevents the source code to perform illegal operation such as accessing invalid memory locations etc.
  • IL( Intermediate language )-to-native translators and optimizer’s :- CLR uses JIT and compiles the IL code to machine code and then executes. CLR also determines depending on platform what is optimized way of running the IL code.

What is a IL

Twist :- What is MSIL or CIL , What is JIT?

(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code is compiled to IL. This IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.

How does the Object Oriented approach improve software development

Ans). The key benefits are:

  • Re-use of previous work: using implementation inheritance and object composition.
  • Real mapping to the problem domain: Objects map to real world and represent vehicles, customers, products etc: with encapsulation.
  • Modular Architecture: Objects, systems, frameworks etc are the building blocks of larger systems. The increased quality and reduced development time are the by-products of the key benefits discussed above. If 90% of the new application consists of proven existing components then only the remaining 10% of the code have to be tested from scratch.

What are the advantages of Object Oriented Programming Languages (OOPL)

Ans). The Object Oriented Programming Languages directly represent the real life objects like Car, Jeep, Account, Customer etc. The features of the OO programming languages like polymorphism, inheritance and
encapsulation make it powerful. [Tip: remember pie which, stands for Polymorphism, Inheritance and
Encapsulation are the 3 pillars of OOPL]

What is the difference between C++ and Java

Ans). Both C++ and Java use similar syntax and are Object Oriented, but:

  • Java does not support pointers. Pointers are inherently tricky to use and troublesome.
  • Java does not support multiple inheritances because it causes more problems than it solves. Instead Javasupports multiple interface inheritance, which allows an object to inherit many method signatures fromdifferent interfaces with the condition that the inheriting object must implement those inherited methods. Themultiple interface inheritance also allows an object to behave polymorphically on those methods. [Refer Q 8 and Q 10 in Java section.]
  • Java does not support destructors but rather adds a finalize() method. Finalize methods are invoked by the garbage collector prior to reclaiming the memory occupied by the object, which has the finalize() method. This means you do not know when the objects are going to be finalized. Avoid using finalize() method to release non-memory resources like file handles, sockets, database connections etc because Java has only a finite number of these resources and you do not know when the garbage collection is going to kick in to release these resources through the finalize() method.
  • Java does not include structures or unions because the traditional data structures are implemented as an object oriented framework (Java collection framework – Refer Q14, Q15 in Java section).
  • All the code in Java program is encapsulated within classes therefore Java does not have global variables or functions.
  • C++ requires explicit memory management, while Java includes automatic garbage collection. [Refer Q32 in Java section].

Give a few reasons for using Java

Ans). Java is a fun language. Let’s look at some of the reasons:

  1. Built-in support for multi-threading, socket communication, and memory management (automatic garbage collection).
  2. Object Oriented (OO).
  3. Better portability than other languages across operating systems.
  4. Supports Web based applications (Applet, Servlet, and JSP), distributed applications (sockets, RMI. EJB etc) and network protocols (HTTP, JRMP etc) with the help of extensive standardised APIs (Application Program Interfaces).

Wednesday, August 18, 2010

What is the use of DBCC commands

DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.
DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC CHECKFILEGROUP - Checks all tables file group for any damage.

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

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

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.

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.

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.

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 referentialintegrity 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.

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. e.g. sp_helpdb, sp_renamedb, sp_depends etc.

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.

What is normalization

Database normalization is a data design and organization process applied to data structures based on rules that help build relational databases. In relational database design, the process of organizing data to minimize redundancy. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions,and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships. 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.

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.

Tuesday, August 17, 2010

What is Meta Data Repository

Meta Data is a data about the data.It also contains

Query statistics

ETL statistics

Business subject area

Source Information

Target Information

Source to Target mapping Information.

What is Data Stage Engine

It is a JAVA engine running at the background.

Construct pipes to execute the following jobs

  1. Output of who should be displayed on the screen with value of total number of users who have logged indisplayed at the bottom of the list.
  2. Output of ls should be displayed on the screen and from this output the lines containing the word ‘poem’should be counted and the count should be stored in a file.
  3. Contents of file1 and file2 should be displayed on the screen and this output should be appended in a file.From output of ls the lines containing ‘poem’ should be displayed on the screen along with the count.
  4. Name of cities should be accepted from the keyboard . This list should be combined with the list presentin a file. This combined list should be sorted and the sorted listshould be stored in a file ‘newcity’.
  5. All files present in a directory dir1 should be deleted any error while deleting should be stored in a file‘errorlog’.

UNIX Commands Interview Questions

  • Construct pipes to execute the following jobs.
  • Explain the following commands.
  • What is the significance of the “tee” command?
  • What does the command “ $who | sort –logfile > newfile” do?
  • What does the command “$ls | wc –l > file1” do?
  • Which of the following commands is not a filter man , (b) cat , (c) pg , (d) head
  • How is the command “$cat file2 “ different from “$cat >file2 and >> redirection operators ?

What is Star Schema

Star Schema is a de-normalized multi-dimensional model. It contains centralized fact tables surrounded by dimensions table.

Dimension Table: It contains a primary key and description about the fact table.

Fact Table: It contains foreign keys to the dimension tables, measures and aggregates.

What is Dimensional Modeling

Dimensional Modeling is a logical design technique that seeks to present the data

in a standard framework that is, intuitive and allows for high performance access.

What is Data Stage Engine

It is a JAVA engine running at the background.

What is Meta Data Repository

Meta Data is a data about the data.It also contains

  • Query statistics
  • ETL statistics
  • Business subject area
  • Source Information
  • Target Information
  • Source to Target mapping Information.

Setting the Polling Interval in SQL server

The service status of various SQL Server components is monitored regularly by SQL Server Enterprise Manager and SQL Server Service Manager. Both allow the monitoring interval to be changed.

Using SQLServerAgent Service

SQLServerAgent is a Windows NT 4.0 or Windows 2000 service that executes jobs, monitors SQL Server, and fires alerts. SQLServerAgent is the service that allows you to automate some administrative tasks. As such, you must start the SQLServerAgent service before your local or multiserver administrative tasks can run automatically. SQL Server Agent runs as a service called SQLServerAgent if it is the default instance or SQLAgent$instancename if it is a named instance.If the SQL Server service and SQL Server Agent service are not configured to start automatically, you must start them manually.

Using SQL Server Service Manager

If you are running Microsoft Windows 98, SQL Server Service Manager can be used start, pause, stop and check the state of local services, though it cannot remotely administer services.

If you have to restart your computer, SQL Server Service Manager appears automatically and the default service is displayed. It is possible to change the default service on the local computer through the SQL Server Service Manager. When you restart the computer, the default service will now be displayed in SQL Server Service Manager. For example, if you change the default service to SQL Server Agent service, and then shut down the computer, the next time you start it, SQL Server Agent service will be displayed in SQL Server Service Manager.

SQL Server Service Manager can also be used to start, pause, or stop an instance of SQL Server 2000 Analysis Services.



To change the default service Service Manager

How to change the default service (Service Manager)

To change the default service

Right-click SQL Server Service Manager, and then click Options.

In the Default Service box, select the new default service to view through SQL Server Service Manager. When you restart the computer, the service that appears is the new default. For example, if you change the default service to SQLServerAgent service and then shut down the computer, the next time you start it, SQLServerAgent service will be displayed in Service Control Manager. You can only change the default service for the local machine.

Using the SQL Server Service

Ans). When you start an instance of SQL Server, you are starting the SQL Server service. After you start the SQL Server service, users can establish new connections to the server. The SQL Server service can be started and stopped as a Microsoft Windows NT® 4.0 or Windows® 2000 service, either locally or remotely. The SQL Server service is referred to as MSSQLServer if it is the default instance, or MSSQL$instancename if it is a named instance.

Starting, Pausing, and Stopping SQL Server

Starting, Pausing, and Stopping SQL Server
Ans). Before you log in to an instance of Microsoft® SQL Server™, you need to know how to start, pause, and stop an instance of SQL Server. After you are logged in, you can perform tasks such as administering the server or querying a database.

Monday, August 16, 2010