J2ee Interview Questions and Answers

1. What makes J2EE suitable for distributed multitiered Applications?
Ans : The J2EE platform uses a multitiered distributed application model. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. The J2EE application parts are:

* Client-tier components run on the client machine.
* Web-tier components run on the J2EE server.
* Business-tier components run on the J2EE server.
* Enterprise information system (EIS)-tier software runs on the EIS server.

2. What is J2EE?
Ans : J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitiered, web-based applications.

3. What do Enterprise JavaBeans components contain?
Ans : Enterprise JavaBeans components contains Business code, which is logic
that solves or meets the needs of a particular business domain such as banking, retail, or finance, is handled by enterprise beans running in the business tier. All the business code is contained inside an Enterprise Bean which receives data from client programs, processes it (if necessary), and sends it to the enterprise information system tier for storage. An enterprise bean also retrieves data from storage, processes it (if necessary), and sends it back to the client program.

4. Is J2EE application only a web-based?
Ans : No, It depends on type of application that client wants. A J2EE application can be web-based or non-web-based. if an application client executes on the client machine, it is a non-web-based J2EE application. The J2EE application can provide a way for users to handle tasks such as J2EE system or application administration. It typically has a graphical user interface created from Swing or AWT APIs, or a command-line interface. When user request, it can open an HTTP connection to establish communication with a servlet running in the web tier.

5. Are JavaBeans J2EE components?
Ans : No. JavaBeans components are not considered J2EE components by the J2EE specification. They are written to manage the data flow between an application client or applet and components running on the J2EE server or between server components and a database. JavaBeans components written for the J2EE platform have instance variables and get and set methods for accessing the data in the instance variables. JavaBeans components used in this way are typically simple in design and implementation, but should conform to the naming and design conventions outlined in the JavaBeans component architecture.

6. Is HTML page a web component?
Ans : No. Static HTML pages and applets are bundled with web components during application assembly, but are not considered web components by the J2EE specification. Even the server-side utility classes are not considered web components, either.

7. What can be considered as a web component?
Ans : J2EE Web components can be either servlets or JSP pages. Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.

8. What is the container?
Ans : Containers are the interface between a component and the low-level platform specific functionality that supports the component. Before a Web, enterprise bean, or application client component can be executed, it must be assembled into a J2EE application and deployed into its container.

9. What are container services?
Ans : A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.

10. What are the components of J2EE application?
Ans: A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components:

1. Application clients and applets are client components.
2. Java Servlet and JavaServer Pages technology components are web components.
3. Enterprise JavaBeans components (enterprise beans) are business components.
4. Resource adapter components provided by EIS and tool vendors.

C Sharp Interview Questions and Answers

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

Ans : 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.

2. What’s the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception?

Ans : A catch block that catches the exception of type System.Exception. You can also omit the parameter data type in this case and just write catch {}.

3. Can multiple catch blocks be executed?

Ans : No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.

4. Why is it a bad idea to throw your own exceptions?

Ans : Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.

5. How’s the DLL Hell problem solved in .NET?

Ans : Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.

6. What’s a satellite assembly?

Ans : 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.

7. What debugging tools come with the .NET SDK?

Ans : CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.

8. What does assert() do?

Ans : In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. The program proceeds without any interruption if the condition is true.

9. Why are there five tracing levels in System.Diagnostics.TraceSwitcher?

Ans : The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.

10. What are three test cases you should go through in unit testing?

Ans : Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).

11. What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?

Ans : SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.

12. Explain ACID rule of thumb for transactions.

Ans : Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), Durable (the values persist if the data had been committed even if the system crashes right after).

C# DotNet Questions

1. What’s the implicit name of the parameter that gets passed into the class’ set method?

Value, and its datatype depends on whatever variable we’re changing.

2. How do you inherit from a class in C#?

Place a colon and then the name of the base class. Notice that it’s double colon in C++.

3. Does C# support multiple inheritance?

No, use interfaces instead.

4. When you inherit a protected class-level variable, who is it available to?

Classes in the same namespace.

5. Are private class-level variables inherited?

Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

6. Describe the accessibility modifier protected internal.

It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).

7. C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?

Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.

8. What’s the top .NET class that everything is derived from?

System.Object.

9. How’s method overriding different from overloading?

When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

10. What does the keyword virtual mean in the method definition?

The method can be over-ridden.

11. Can you declare the override method static while the original method is non-static?

No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

12. Can you override private virtual methods?

No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

13. Can you prevent your class from being inherited and becoming a base class for some other classes?

Yes, that’s what keyword sealed in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class WhateverBaseClassName. It’s the same concept as final class in Java.

14. Can you allow class to be inherited, but prevent the method from being over-ridden?

Yes, just leave the class public and make the method sealed.

15. What’s an abstract class?

A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.

Java Fundamental-X

1. What is J2EE Connector?

The J2EE Connector API is used by J2EE tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. Each type of database or EIS has a different resource adapter.

2. What is JAAP?

The Java Authentication and Authorization Service (JAAS) provide a way for a J2EE application to authenticate and authorize a specific user or group of users to run it. It is a standard Pluggable Authentication Module (PAM) framework that extends the Java 2 platform security architecture to support user-based authorization.

3. What is Model 1?

Using JSP technology alone to develop Web page. Such term is used in the earlier JSP specification. Model 1 architecture is suitable for applications that have very simple page flow, have little need for centralized security control or logging, and change little over time. Model 1 applications can often be refactored to Model 2 when application requirements change.

4. What is Model 2?

Using JSP and Servlet together to develop Web page. Model 2 applications are easier to maintain and extend, because views do not refer to each other directly.

5. What is Struts?

A Web page development framework. Struts combine Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.

6. How is the MVC design pattern used in Struts framework?

In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application's business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make an application significantly easier to create and maintain.

Controller--Servlet controller which supplied by Struts itself; View --- what you can see on the screen, a JSP page and presentation components; Model --- System state and a business logic JavaBeans.

7. What does web module contain?

The web module contains:

o JSP files,

o class files for Servlets,

o GIF and HTML files, and

o A Web deployment descriptor.

Web modules are packaged as JAR files with a .war (Web Archive) extension.

8. What APIs are available for developing a J2EE application?

o Enterprise JavaBeans Technology(3 beans: Session Beans, Entity Beans and Message-Driven Beans)

o JDBC API(application level interface and service provider interface or driver)

o Java Servlets Technology(Servlet)

o Java ServerPage Technology(JSP)

o Java Message Service(JMS)

o Java Naming and Directory Interface(JNDI)

o Java Transaction API(JTA)

o JavaMail API

o JavaBeans Activation Framework(JAF used by JavaMail)

o Java API for XML Processing(JAXP,SAX, DOM, XSLT)

o Java API for XML Registries(JAXR)

o Java API for XML-Based RPC(JAX-RPC)-SOAP standard and HTTP

o SOAP with Attachments API for Java(SAAJ)-- low-level API upon which JAX-RPC depends

o J2EE Connector Architecture

o Java Authentication and Authorization Service(JAAS)

Java Fundamental-IX

1. Are JavaBeans J2EE components?

NO. JavaBeans components are not considered J2EE components by the J2EE specification. JavaBeans components written for the J2EE platform have instance variables and get and set methods for accessing the data in the instance variables. JavaBeans components used in this way are typically simple in design and implementation, but should conform to the naming and design conventions outlined in the JavaBeans component architecture.

2. Is HTML page a web component?

NO. Static HTML pages and applets are bundled with web components during application assembly, but are not considered web components by the J2EE specification. Even the server-side utility classes are not considered web components, either.

3. What is the container?

A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.

4. What is the web container?

Servlet and JSP containers are collectively referred to as Web containers.

5. What is the thin client?

A thin client is a lightweight interface to the application that does not have such operations like query databases, execute complex business rules, or connect to legacy applications.

6. What are types of J2EE clients?

o Applets

o Application clients

o Java Web Start-enabled rich clients, powered by Java Web Start technology.

o Wireless clients, based on Mobile Information Device Profile (MIDP) technology.

7. What is deployment descriptor?

A deployment descriptor is an Extensible Markup Language (XML) text-based file with an .xml extension that describes a component's deployment settings. A J2EE application and each of its modules has its own deployment descriptor.

8. What is the EAR file?

An EAR file is a standard JAR file with an .ear extension, named from Enterprise Archive file. A J2EE application with all of its modules is delivered in EAR file.

9. What are JTA and JTS?

JTA is the abbreviation for the Java Transaction API. JTS is the abbreviation for the Java Transaction Service. JTA provides a standard interface and allows you to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code doesn't call the JTS methods directly. Instead, it invokes the JTA methods, which then call the lower-level JTS routines.

Therefore, JTA is a high level transaction interface that your application uses to control transaction. And JTS is a low level transaction interface and EJBs uses behind the scenes (client code doesn't directly interact with JTS. It is based on object transaction service (OTS) which is part of CORBA.

10. What is JAXP?

JAXP stands for Java API for XML. XML is a language for representing and describing text-based data which can be read and handled by any program or tool that uses XML APIs.

Java Fundamental-VIII

1. What is J2EE?

J2EE is an environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multi tiered, and web-based applications.

2. What is the J2EE module?

A J2EE module consists of one or more J2EE components for the same container type and one component deployment descriptor of that type.

3. What are the components of J2EE application?

A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components:

o Application clients and applets are client components.

o Java Servlets and Java Server Pages TM (JSPTM) technology components are web components.

o Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are business components.

o Resource adapter components provided by EIS and tool vendors.

4. What are the four types of J2EE modules?

1. Application client module

2. Web module

3. Enterprise JavaBeans module

4. Resource adapter module

5. What does application client module contain?

The application client module contains:

o class files,

o an application client deployment descriptor.

Application client modules are packaged as JAR files with a .jar extension.

6. What does Enterprise JavaBeans module contain?

The Enterprise JavaBeans module contains:

o class files for enterprise beans

o An EJB deployment descriptor.

EJB modules are packaged as JAR files with a .jar extension.

7. What does resource adapt module contain?

The resource adapt module contains:

o all Java interfaces,

o classes,

o native libraries,

o other documentation,

o A resource adapter deployment descriptor.

Resource adapter modules are packages as JAR files with a .rar (Resource adapter Archive) extension.

8. Is J2EE application only a web-based?

NO. A J2EE application can be web-based or non-web-based. If an application client executes on the client machine, it is a non-web-based J2EE application. The J2EE application can provide a way for users to handle tasks such as J2EE system or application administration. It typically has a graphical user interface created from Swing or AWT APIs, or a command-line interface. When user request, it can open an HTTP connection to establish communication with a Servlet running in the web tier.

Database System-V

1. 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.

2. 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, ea ch 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.

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

A clustered index is a special type of index that reorders the wa y 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.

4. What are the different index configurations a table can have?

A table can have one of the following index configurations:

a. No indexes

b. A clustered index

c. A clustered index and many nonclustered indexes

d. A nonclustered index

e. Many nonclustered indexes

5 .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:

a. Declare cursor

b. Open cursor

c. Fetch row from the cursor

d. Process fetched row

e. Close cursor

f. Deallocate cursor

Database System-IV

1. 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 a cross 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 ha s the capability to recombine the data items from different files, providing powerful tools for data usage.

2. 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.

3. What are different normalization forms?

1NF: Eliminate Repeating Group

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.

4. 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.

5. 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 atta ched 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.

Database System-III

1. What is a "primary key"?

Ans : A PRIMARY INDEX or PRIMARY KEY is something which comes mainly from database theory. From its behavior is almost the same as an UNIQUE INDEX, i.e. there may only be one of each value in this column. If you call such an INDEX PRIMARY instead of UNIQUE, you say something about your table design, which I am not able to explain in few words. Primary Key is a type of a constraint enforcing uniqueness and data integrity for each row of a table. All columns participating in a primary key constraint must possess the NOT NULL property.

2. What is a "functional dependency"? How does it relate to database table design?

Ans : Functional dependency relates to how one object depends upon the other in the database. for example, procedure/function sp2 may be called by procedure sp1. Then we say that sp1 has functional dependency on sp2.

3. What is a "trigger"?

Ans : Triggers are stored procedures created in order to enforce integrity rules in a database. A trigger is executed every time a data-modification operation occurs (i.e., insert, update or delete). Triggers are executed automatically on occurance of one of the data-modification operations. A trigger is a database object directly associated with a particular table. It fires whenever a specific statement/type of statement is issued against that table. The types of statements are insert,update,delete and query statements. Basically, trigger is a set of SQL statements A trigger is a solution to the restrictions of a constraint. For instance: 1.A database column cannot carry PSEUDO columns as criteria where a trigger can. 2. A database constraint cannot refer old and new values for a row where a trigger can.

4. Why can a "group by" or "order by" clause be expensive to process?

Ans : Processing of "group by" or "order by" clause often requires creation of Temporary tables to process the results of the query. Which depending of the result set can be very expensive.

5. What is "index covering" of a query?

Ans : Index covering means that "Data can be found only using indexes, without touching the tables"

6. What is a SQL view?

Ans : An output of a query can be stored as a view. View acts like small table which meets our criterion. View is a precomplied SQL query which is used to select data from one or more tables. A view is like a table but it doesn’t physically take any space. View is a good way to present data in a particular format if you use that query quite often. View can also be used to restrict users from accessing the tables directly.

7. What are two methods of retrieving SQL?

Ans : Use SELECT Query and Projection Relational Algebra to retrieve SQL.

8. What cursor type do you use to retrieve multiple recordsets?

Ans : Explicit Cursor has been used to retrieve multiple records at a time.

9. What types of join algorithms can you have?

Ans : Natural Join, Equi Join, Inner Join, Outer Join (Left Outer Join ,Right Outer Join, Full Outer Join), Cross Join, Self Join, etc.

Database System-II

1. What is the difference between a "where" clause and a "having" clause?

Ans : "Where" is a kind of restiriction statement. You use where clause to restrict all the data from DB.Where clause is using before result retrieving. But Having clause is using after retrieving the data.Having clause is a kind of filtering command.

2. What is the basic form of a SQL statement to read data out of a table?

Ans : The basic form to read data out of table is ‘SELECT * FROM table_name; ‘ An answer: ‘SELECT * FROM table_name WHERE xyz= ‘whatever’;’ cannot be called basic form because of WHERE clause.

3. What structure can you implement for the database to speed up table reads?

Ans :  Follow the rules of DB tuning we have to: 1] properly use indexes ( different types of indexes) 2] properly locate different DB objects across different tablespaces, files and so on.3] create a special space (tablespace) to locate some of the data with special datatype ( for example CLOB, LOB and …)

4. What are the tradeoffs with having indexes?

Ans : 1. Faster selects, slower updates. 2. Extra storage space to store indexes. Updates are slower because in addition to updating the table you have to update the index.

5. What is a "join"?

Ans : ‘join’ used to connect two or more tables logically with or without common field.

6. What is "normalization"?

Ans : "Denormalization"? Why do you sometimes want to denormalize? - Normalizing data means eliminating redundant information from a table and organizing the data so that future changes to the table are easier. Denormalization means allowing redundancy in a table. The main benefit of denormalization is improved performance with simplified data retrieval and manipulation. This is done by reduction in the number of joins needed for data processing.

7. What is a "constraint"?

Ans : A constraint allows you to apply simple referential integrity checks to a table. There are four primary types of constraints that are currently supported by SQL Server: PRIMARY/UNIQUE - enforces uniqueness of a particular table column. DEFAULT - specifies a default value for a column in case an insert operation does not provide one. FOREIGN KEY - validates that every value in a column exists in a column of another table. CHECK - checks that every value stored in a column is in some specified list. Each type of constraint performs a specific type of action. Default is not a constraint. NOT NULL is one more constraint which does not allow values in the specific column to be null. And also it the only constraint which is not a table level constraint.

8. What types of index data structures can you have?

Ans :  An index helps to faster search values in tables. The three most commonly used index-types are: - B-Tree: builds a tree of possible values with a list of row IDs that have the leaf value. Needs a lot of space and is the default index type for most databases. - Bitmap: string of bits for each possible value of the column. Each bit string has one bit for each row. Needs only few space and is very fast.(however, domain of value cannot be large, e.g. SEX(m,f); degree(BS,MS,PHD) - Hash: A hashing algorithm is used to assign a set of characters to represent a text string such as a composite of keys or partial keys, and compresses the underlying data. Takes longer to build and is supported by relatively few databases.