SQL Server Interview Tips

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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....

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...

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...

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 ...

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...

What is cursors?
Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis,...

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...


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....


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 ...


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...

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..

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...
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Plans and Goals

Plans are taken to achieve goals. Goals may be either short or long term. Generally, long term goals can take about three to five years to achieve, while short term goals are reachable in a year or so. We set goals only when we plan what we want to accomplish. It could be as simple as cleaning the house or finishing an assignment or as complex as transforming a developing country into a developed one.

A plan needs to be written. A written plan provides a visible objective to work for. An example of a written plan is a family budget. A budget shows where the family is financially, how much the family is currently spending, and how much the family can spend according to the current income.

The primary ingredients necessary to develop a plan are goals. Plans are generally divided into
1. short-range plans, and
2. long-range plans.

Short-range plans are basically day-to-day occurrences.

Long range planning is very important. Everyone has a responsibility to plan well, to have good sound objectives, and to achieve success. There should also be some specific goals developed for the use of surplus funds. We should also be clear about how much should be invested and how much should be set aside for domestic wants?

Future income should not be depended upon. It is also important to be moral while achieving the goals. It is necessary to monitor that family is not trapped into anything that is unethical, immoral, or dishonest. In addition, there should be a family contingency plan in the event wealth is lost due to unforeseen disaster.

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GROUP DISCUSSION - Tips

In a group discussion a candidate creates a first impression about himself on the testing authorities and on the group members. This impression is very important as far as recruitment or selection is conn...

FACTORS THAT ARE IMPORTANT IN A GROUP DISCUSSION:

1. POWER OF EXPRESSION: The ideas must be expressed clearly, fluently and logically.
2. KNOWLEDGE: The range of ideas and depth of thoughts go a long way in favouring a candidate.
3. SOCIAL ADAPTABILITY: Co-operative attitude, readiness to accept mistakes, ability to accept criticism with grace and consideration for the thought of others are the qualities that are looked for in a candidate.
4. FLEXIBILITY: A selfless attitude and receptive natur....


TIPS TO THE CANDIDATE:
 Be active and interested in the discussion. The candidate must remain alert to the activities of the group and must not allow the mind to wander away. Concentrate on and look at the individual who speaks with cheer and smile.
 Listen to the briefing of the subject of discussion and understan....



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ASP.NET Interview Questions

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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.

What’s the difference between Response.Write() andResponse.Output.Write()?
Response.Output.Write() allows you to write formatted output.

What methods are fired during the page load?
Init() - when the page is instantiated
Load() - when the page is loaded into server memory
PreRender() - the brief moment before the page is displayed to the user as HTML
Unload() - when page finishes loading.

When during the page processing cycle is ViewState available?
After the Init() and before the Page_Load(), or OnLoad() for a control.

What namespace does the Web page belong in the .NET Framework class hierarchy?
System.Web.UI.Page

Where do you store the information about the user’s locale?
System.Web.UI.Page.Culture

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Job Interview Q & A

Do you have any weaknesses?
Trick question. If you know about weakness, they are no longer blind spots. Do not reveal any personal areas of ...

What is your greatest strength?
Numerous answers are good, just stay positive. A few good examples: Your ability to prioritize, Your problem-solving skills, Your ability to ....

What have you learned from mistakes on the job?
Here you have to come up with something or you strain credibility. Make it small, well intentioned mistake with a positive lesson learned. An example would ...

Why should you be hired for this job?
Point out how your talents and how they meet what the organization needs. Do not mention any other job candidates and try to make a comparison. Try to ....

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Men to wear for an interview

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Dressing Right for The Interview

"Although proper dressing by itself will not get you the job, a poor dress sense may exclude you from further consideration," warns Gerry Ditching, managing partner of Filgifts.com. Besides, given two equally good applicants, the company may choose to hire the person who is dressed more professionally. Here are some tips to give you a headstart.

For MEN:
Long-sleeved shirt and dark slacks. White is still the safest and the best color for shirts. The colour is also appropriate for our tropical weather. Also acceptable: pale shades such as beige, blue, and other pastels.

Tuck in the shirt and do not roll up the sleeves. Never wear a short-sleeved shirt to an interview or any business purpose. Wearing a short-sleeved shirt will destroy your executive image.

Ties. Optional. But if you do wear one, choose a conservative....

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What to wear for an interview - Women

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Dressing Right for The Interview

"Although proper dressing by itself will not get you the job, a poor dress sense may exclude you from further consideration," warns Gerry Ditching, managing partner of Filgifts.com. Besides, given two equally good applicants, the company may choose to hire the person who is dressed more professionally. Here are some tips to give you a headstart.

For WOMEN

Three-piece business suits, blouse and skirt or slacks, and cardigan twin-sets. Sleeveless shirts should be rejected. Short-sleeved blouses are okay when they are tailor-cut or have features such as a sports collar or double breast design to create a business-like look. Skirts can either be long provided it does not create a Cinderella or barn-dance look or short where it falls no shorter than two inches from the knee. Nothing too revealing, please!

Panty-hose or stockings. A must for professional grooming, but nothing with overly fussy patterns. Bring an extra pair, just in case the ones you are wearing run.

Shoes. Closed shoes or pumps......

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How To face HR Interview?

How To face HR Interview.. see here.
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How To face HR Interview

1. Are your work practices similar or different from ours? (If Experienced)
2. Describe our (products/services).
3. Describe our company for me.
4. Describe our corporate environment for me.
5. Describe your work (methods/processes) in comparison to ours? (If Experienced)
6. Do our competitors do things that we should be doing?
7. Do you have any concerns about working here?
8. Do you have any questions about (our/this) company?
9. Do you know how long we have been in business?
10. Do you know what products we make?
11. How could you have prevented your (judgmental) errors?
12. How do you think our company determines success?
13. How does you present employer communicate with others in your deprtment? (If experienced)
14. Tell me how you found out information about (our/this) company?

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JAVA & J2EE Interview FAQ

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JAVA & J2EE Interview Questions and Answers

What is the use of bin and lib in JDK?- Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.

What is casting?- Casting is used to convert the value of one type to another.

What is final, finalize() and finally?- final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents other programmers from subclassing a secure class to invoke insecure methods. A final method can’t be overridden. A final variable can’t change from its initialized value. finalize() : finalize() method is used just before an object is destroyed and can be called just prior to garbage collection. finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address this contingency.

What is UNICODE?- Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.

What is Garbage Collection and how to call it explicitly?- When an object i .....

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Interview Tips

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Great interviews arise from careful groundwork. You can ace your next interview if you:
# Dress appropriately for the industry; err on the side of being conservative to show you take the interview seriously. Your personal grooming and cleanliness should be impeccable.# Know the exact time and location of your interview; know how long it takes to get there, park, find a rest room to freshen up, etc.# Arrive early; 10 minutes prior to the interview start time.# Treat other people you encounter with courtesy and respect. Their opinions of you might be solicited during hiring decisions.# Offer a firm handshake, make eye contact, and have a friendly expression when you are greeted by your interviewer. Set goals for the interview. It is your job to leave the meeting feeling secure that the interviewer knows as much as he or she possibly can about your skills, abilities, experience...
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SQL - Interview Questions

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.

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.

What are different normalization forms?

1NF: Eliminate Repeating GroupsMake 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 DataIf an attribute depends on only part of a multi-valued key, remove it to a separate table.

3NF: Eliminate Columns Not Dependent On KeyIf 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 FormIf there are non-trivial dependencies between candidate key attributes, separate them out into distinct tables.

4NF: Isolate Independent Multiple RelationshipsNo table may contain two or more 1:n or n:m relationships that are not directly related.

5NF: Isolate Semantically Related Multiple RelationshipsThere may be practical constrains on information that justify separating logically related many-to-many relationships.

ONF: Optimal Normal FormA model limited to only simple (elemental) facts, as expressed in Object Role Model notation.

DKNF: Domain-Key Normal FormA 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 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 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.

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 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 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 are the different index configurations a table can have?

A table can have one of the following index configurations:No indexesA clustered indexA clustered index and many nonclustered indexesA nonclustered indexMany nonclustered indexes
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 cursorOpen cursorFetch row from the cursorProcess fetched rowClose cursorDeallocate cursor

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 a Linked Server?

Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements. With a linked server, you can create very clean, easy to follow, SQL statements that allow remote data to be retrieved, joined and combined with local data.Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.

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 casesensitivity, accent marks, kana character types and character width.

What are different type of Collation Sensitivity?

Case sensitivityA and a, B and b, etc.

Accent sensitivitya and á, o and ó, etc.

Kana SensitivityWhen Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana sensitive.

Width sensitivityWhen a single-byte character (half-width) and the same character when represented as a double-byte character (full-width) are treated differently then it is width sensitive.

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.

How to implement one-to-one, one-to-many and many-to-many relationships whiledesigning 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.

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).

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 thepage 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.

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.

DELETE is DML Command.

DELETE does not reset identity of the table.

Interview DOs and DON'Ts

Interview DOs

• Do Dress appropriately for the industry; err on the side of being conservative to show you take the interview seriously. Your personal grooming and cleanliness should be impeccable.
  
• Do Know the exact time and location of your interview; know how long it takes to get there, park, find a rest room to freshen up, etc.
  
• Do Arrive early; 10 minutes prior to the interview start time.
  
• Do Treat other people you encounter with courtesy and respect. Their opinions of you might be solicited during hiring decisions.
  
• Do Offer a firm handshake, make eye contact, and have a friendly expression when you are greeted by your interviewer.
  
• Do Listen to be sure you understand your interviewer's name and the correct pronunciation.
  
• Do Even when your interviewer gives you a first and last name, address your interviewer by title (Ms., Mr., Dr.) and last name, until invited to do otherwise.
  
• Do Maintain good eye contact during the interview.
  
• Do Sit still in your seat; avoid fidgeting and slouching.
  
• Do Respond to questions and back up your statements about yourself with specific examples whenever possible.
  
• Do Ask for clarification if you don't understand a question.
  
• Do Be thorough in your responses, while being concise in your wording.
  
• Do Be honest and be yourself. Dishonesty gets discovered and is grounds for withdrawing job offers and for firing. You want a good match between yourself and your employer. If you get hired by acting like someone other than yourself, you and your employer will both be unhappy.
  
• Do Treat the interview seriously and as though you are truly interested in the employer and the opportunity presented.
  
• Do Exhibit a positive attitude. The interviewer is evaluating you as a potential co-worker. Behave like someone you would want to work with.
  
• Do Have intelligent questions prepared to ask the interviewer. Having done your research about the employer in advance, ask questions which you did not find answered in your research.
  
• Do Evaluate the interviewer and the organization s/he represents. An interview is a two-way street. Conduct yourself cordially and respectfully, while thinking critically about the way you are treated and the values and priorities of the organization.
  
• Do Do expect to be treated appropriately. If you believe you were treated inappropriately or asked questions that were inappropriate or made you uncomfortable, discuss this with a Career Services advisor or the director.
  
• Do Make sure you understand the employer's next step in the hiring process; know when and from whom you should expect to hear next. Know what action you are expected to take next, if any.
  
• Do When the interviewer concludes the interview, offer a firm handshake and make eye contact. Depart gracefully.
  
• Do After the interview, make notes right away so you don't forget critical details.
  
• Do Write a thank-you letter to your interviewer promptly

Interview DON'Ts

• Don't Don't make excuses. Take responsibility for your decisions and your actions.
  
• Don't Don't make negative comments about previous employers or professors (or others).
  
• Don't Don't falsify application materials or answers to interview questions.
  
• Don't Don't treat the interview casually, as if you are just shopping around or doing the interview for practice. This is an insult to the interviewer and to the organization.
  
• Don't Don't give the impression that you are only interested in an organization because of its geographic location.
  
• Don't Don't give the impression you are only interested in salary; don't ask about salary and benefits issues until the subject is brought up by your interviewer.
  
• Don't Don't act as though you would take any job or are desperate for employment.
  
• Don't Don't make the interviewer guess what type of work you are interested in; it is not the interviewer's job to act as a career advisor to you.
  
• Don't Don't be unprepared for typical interview questions. You may not be asked all of them in every interview, but being unprepared looks foolish.
  
• Don't A job search can be hard work and involve frustrations; don't exhibit frustrations or a negative attitude in an interview.
  
• Don't Don't go to extremes with your posture; don't slouch, and don't sit rigidly on the edge of your chair.
  
• Don't Don't assume that a female interviewer is "Mrs." or "Miss." Address her as "Ms." unless told otherwise. Her marital status is irrelevant to the purpose of the interview.
  
• Don't Don't chew gum or smell like smoke.
  
• Don't Don't allow your cell phone to sound during the interview. (If it does, apologize quickly and ignore it.) Don't take a cell phone call.
  
• Don't Don't take your parents, your pet (an assistance animal is not a pet in this circumstance), spouse, fiance, friends or enemies to an interview. If you are not grown up and independent enough to attend an interview alone, you're insufficiently grown up and independent for a job. (They can certainly visit your new city, at their own expense, but cannot attend your interview.)

RDBMS Concepts - Part 2

Continues....

40. What is Functional Dependency?
A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.

41. When is a functional dependency F said to be minimal?
¢ Every dependency in F has a single attribute for its right hand side.
¢ We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.
¢ We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

42. What is Multivalued dependency?
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
¢ t3[x] = t4[X] = t1[X] = t2[X]
¢ t3[Y] = t1[Y] and t4[Y] = t2[Y]
¢ t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]

43. What is Lossless join property?
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

44. What is 1 NF (Normal Form)?
The domain of attribute must include only atomic (simple, indivisible) values.

45. What is Fully Functional dependency?
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

46. What is 2NF?
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

47. What is 3NF?
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
¢ X is a Super-key of R.
¢ A is a prime attribute of R.
In other words, if every non prime attribute is non-transitively dependent on primary key.

48. What is BCNF (Boyce-Codd Normal Form)?
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

49. What is 4NF?
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
¢ X is subset or equal to (or) XY = R.
¢ X is a super key.

50. What is 5NF?
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
¢ Ri = R for some i.
¢ The join dependency is implied by the set of FD, over R in which the left side is key of R.

51. What is Domain-Key Normal Form?
A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

RDBMS concepts - Part 1

1. What is database?

A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.


2. What is DBMS?

It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.


3. What is a Database system?

The database and DBMS software together is called as Database system.


4. Advantages of DBMS?

Ø Redundancy is controlled.

Ø Unauthorised access is restricted.

Ø Providing multiple user interfaces.

Ø Enforcing integrity constraints.

Ø Providing backup and recovery.


5. Disadvantage in File Processing System?

Ø Data redundancy & inconsistency.

Ø Difficult in accessing data.

Ø Data isolation.

Ø Data integrity.

Ø Concurrent access is not possible.

Ø Security Problems.


6. Describe the three levels of data abstraction?

The are three levels of abstraction:

Ø Physical level: The lowest level of abstraction describes how data are stored.

Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

Ø View level: The highest level of abstraction describes only part of entire database.

7. Define the "integrity rules"

There are two Integrity rules.

Ø Entity Integrity: States that “Primary key cannot have NULL value”

Ø Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.


8. What is extension and intension?

Extension -

It is the number of tuples present in a table at any instance. This is time dependent.

Intension -

It is a constant value that gives the name, structure of table and the constraints laid on it.


9. What is System R? What are its two major subsystems?

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.

Its two subsystems are

Ø Research Storage

Ø System Relational Data System.


10. How is the data structure of System R different from the relational structure?

Unlike Relational systems in System R

Ø Domains are not supported

Ø Enforcement of candidate key uniqueness is optional

Ø Enforcement of entity integrity is optional

Ø Referential integrity is not enforced


11. What is Data Independence?

Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.

Two types of Data Independence:

Ø Physical Data Independence: Modification in physical level should not affect the logical level.

Ø Logical Data Independence: Modification in logical level should affect the view level.

NOTE: Logical Data Independence is more difficult to achieve


12. What is a view? How it is related to data independence?

A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.

Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.


13. What is Data Model?

A collection of conceptual tools for describing data, data relationships data semantics and constraints.


14. What is E-R model?

This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.


15. What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.


16. What is an Entity?

It is a 'thing' in the real world with an independent existence.


17. What is an Entity type?

It is a collection (set) of entities that have same attributes.


18. What is an Entity set?

It is a collection of all entities of particular entity type in the database.


19. What is an Extension of entity type?

The collections of entities of a particular entity type are grouped together into an entity set.


20. What is Weak Entity set?

An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.


21. What is an attribute?

It is a particular property, which describes the entity.


22. What is a Relation Schema and a Relation?

A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).


23. What is degree of a Relation?

It is the number of attribute of its relation schema.


24. What is Relationship?

It is an association among two or more entities.


25. What is Relationship set?

The collection (or set) of similar relationships.


26. What is Relationship type?

Relationship type defines a set of associations or a relationship set among a given set of entity types.


27. What is degree of Relationship type?

It is the number of entity type participating.


25. What is DDL (Data Definition Language)?

A data base schema is specifies by a set of definitions expressed by a special language called DDL.


26. What is VDL (View Definition Language)?

It specifies user views and their mappings to the conceptual schema.


27. What is SDL (Storage Definition Language)?

This language is to specify the internal schema. This language may specify the mapping between two schemas.


28. What is Data Storage - Definition Language?

The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.


29. What is DML (Data Manipulation Language)?

This language that enable user to access or manipulate data as organised by appropriate data model.

Ø Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.

Ø Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.


31. What is DML Compiler?

It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.


32. What is Query evaluation engine?

It executes low-level instruction generated by compiler.


33. What is DDL Interpreter?

It interprets DDL statements and record them in tables containing metadata.


34. What is Record-at-a-time?

The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.


35. What is Set-at-a-time or Set-oriented?

The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.


36. What is Relational Algebra?

It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.


37. What is Relational Calculus?

It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.


38. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus

The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL

The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.

Operating Systems - Basic Stuffs

Following are a few basic questions that cover the essentials of OS:


1. Explain the concept of Reentrancy.

It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.

Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.


2. Explain Belady's Anomaly.

Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process' virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.


3. What is a binary semaphore? What is its use?

A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual exclusion and synchronize concurrent processes.


4. What is thrashing?

It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.


5. List the Coffman's conditions that lead to a deadlock.

Ø Mutual Exclusion: Only one process may use a critical resource at a time.

Ø Hold & Wait: A process may be allocated some resources while waiting for others.

Ø No Pre-emption: No resource can be forcible removed from a process holding it.

Ø Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.



6. What are short-, long- and medium-term scheduling?

Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.

Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.

Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.


7. What are turnaround time and response time?

Turnaround time is the interval between the submission of a job and its completion. Response time is the interval between submission of a request, and the first response to that request.


8. What are the typical elements of a process image?

Ø User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified.

Ø User program: The instructions to be executed.

Ø System Stack: Each process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.

Ø Process control Block (PCB): Info needed by the OS to control processes.


9. What is the Translation Lookaside Buffer (TLB)?

In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most recently used. Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.


10. What is the resident set and working set of a process?

Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)


11. When is a system in safe state?

The set of dispatchable processes is in a safe state if there exists at least one temporal order in which all processes can be run to completion without resulting in a deadlock.


12. What is cycle stealing?

We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.


13. What is meant by arm-stickiness?

If one or a few processes have a high access rate to data on one track of a storage disk, then they may monopolize the device by repeated requests to that track. This generally happens with most common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are more likely to be affected by this than low density ones.


14. What are the stipulations of C2 level security?

C2 level security provides for:

Ø Discretionary Access Control
Ø Identification and Authentication
Ø Auditing
Ø Resource reuse


15. What is busy waiting?

The repeated execution of a loop of code while waiting for an event to occur is called busy-waiting. The CPU is not engaged in any real productive activity during this period, and the process does not progress toward completion.


16. Explain the popular multiprocessor thread-scheduling strategies.

Ø Load Sharing: Processes are not assigned to a particular processor. A global queue of threads is maintained. Each processor, when idle, selects a thread from this queue. Note that load balancing refers to a scheme where work is allocated to processors on a more permanent basis.

Ø Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way to reduce synchronization blocking, and minimize process switching. Group scheduling predated this strategy.

Ø Dedicated processor assignment: Provides implicit scheduling defined by assignment of threads to processors. For the duration of program execution, each program is allocated a set of processors equal in number to the number of threads in the program. Processors are chosen from the available pool.

Ø Dynamic scheduling: The number of thread in a program can be altered during the course of execution.


17. When does the condition 'rendezvous' arise?

In message passing, it is the condition in which, both, the sender and receiver are blocked until the message is delivered.


18. What is a trap and trapdoor?

Trapdoor is a secret undocumented entry point into a program used to grant access without normal methods of access authentication. A trap is a software interrupt, usually the result of an error condition.


19. What are local and global page replacements?

Local replacement means that an incoming page is brought in only to the relevant process' address space. Global replacement policy allows any page frame from any process to be replaced. The latter is applicable to variable partitions model only.


20. Define latency, transfer and seek time with respect to disk I/O.

Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.


21. Describe the Buddy system of memory allocation.

Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.


22. What is time-stamping?

It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti (b) if Ti=Tj and i


23. How are the wait/signal operations for monitor different from those for semaphores?

If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program.



24. In the context of memory management, what are placement and replacement algorithms?

Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.


25. In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?

For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.

With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.


26. What are demand- and pre-paging?

With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.


27. Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?

Yes.


28. What is page cannibalizing?

Page swapping or page replacements are called page cannibalizing.


29. What has triggered the need for multitasking in PCs?

Ø Increased speed and memory capacity of microprocessors together with the support fir virtual memory and
Ø Growth of client server computing


30. What are the four layers that Windows NT have in order to achieve independence?

Ø Hardware abstraction layer
Ø Kernel
Ø Subsystems
Ø System Services.


31. What is SMP?

To achieve maximum efficiency and reliability a mode of operation known as symmetric multiprocessing is used. In essence, with SMP any process or threads can be assigned to any processor.


32. What are the key object oriented concepts used by Windows NT?

Ø Encapsulation

Ø Object class and instance


33. Is Windows NT a full blown object oriented operating system? Give reasons.

No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within one executive component and are not represented as objects and it does not support object oriented capabilities .


34. What is a drawback of MVT?

It does not have the features like

Ø ability to support multiple processors
Ø virtual storage
Ø source level debugging


35. What is process spawning?

When the OS at the explicit request of another process creates a process, this action is called process spawning.


36. How many jobs can be run concurrently on MVT?

15 jobs


37. List out some reasons for process termination.

Ø Normal completion
Ø Time limit exceeded
Ø Memory unavailable
Ø Bounds violation
Ø Protection error
Ø Arithmetic error
Ø Time overrun
Ø I/O failure
Ø Invalid instruction
Ø Privileged instruction
Ø Data misuse
Ø Operator or OS intervention
Ø Parent termination.


38. What are the reasons for process suspension?

Ø swapping

Ø interactive user request

Ø timing

Ø parent process request


39. What is process migration?

It is the transfer of sufficient amount of the state of process from one machine to the target machine


40. What is mutant?

In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of ownership.


41. What is an idle thread?

The special thread a dispatcher will execute when no ready thread is found.


42. What is FtDisk?

It is a fault tolerance disk driver for Windows NT.


43. What are the possible threads a thread can have?

Ø Ready
Ø Standby
Ø Running
Ø Waiting
Ø Transition
Ø Terminated.


44. What are rings in Windows NT?

Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.


45. What is Executive in Windows NT?

In Windows NT, executive refers to the operating system code that runs in kernel mode.


46. What are the sub-components of I/O manager in Windows NT?

Ø Network redirector/ Server
Ø Cache manager.
Ø File systems
Ø Network driver
Ø Device driver


47. What are DDks? Name an operating system that includes this feature.

DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT includes DDks.


48. What level of security does Windows NT meets?

C2 level security.