by Dinesh Thakur Category: RDBMS

It is used to determine an efficient file organization for each base relation. For example, if we want to retrieve student records in alphabetical order of name, sorting the file by student name is a good file organization. However, if we want to retrieve all students whose marks is in a certain range, a file ordered by student name would not be a good file organization. Some file organizations are efficient for bulk loading data into the database but inefficient for retrieve and other activities.
The objective of this selection is to choose an optimal file organization for each relation.



 
by Dinesh Thakur Category: RDBMS

Transaction processing systems usually allow multiple transactions to run concurrently. By allowing multiple transactions to run concurrently will improve the performance of the system in terms of increased throughout or improved response time, but this allows causes several complications with consistency of the data. Ensuring consistency in spite of concurrent execution of transaction require extra work, which is performed by the concurrency controller system of DBMS.



 
by Dinesh Thakur Category: RDBMS

A transaction is a set of changes that must all be made together. It is a program unit whose execution mayor may not change the contents of a database. Transaction is executed as a single unit. If the database was in consistent state before a transaction, then after execution of the transaction also, the database must be in a consistate. For example, a transfer of money from one bank account to another requires two changes to the database both must succeed or fail together.



 
by Dinesh Thakur Category: RDBMS

A relation R is in Fifth Normal Form (5NF) if and only if the following conditions are satisfied simultaneously:
1. R is already in 4NF.
2. It cannot be further non-loss decomposed.
5NF is of little practical use to the database designer, but it is of interest from a theoretical point of view and a discussion of it is included here to complete the picture of the further normal forms.



 
by Dinesh Thakur Category: RDBMS

What is Key?

A database consists of tables, which consist of records, which further consist of fields.

This below figure provides an example of a typical table consisting of STUDENT details:



 
by Dinesh Thakur Category: RDBMS

A relation R is in Fourth Normal Form (4NF) if and only if the following conditions are satisfied simultaneously:

R is already in 3NF or BCNF.

If it contains no multi-valued dependencies.

 
by Dinesh Thakur Category: RDBMS

To eliminate these anomalies in 3NF relations, it is necessary to carry out the normalization process to the next higher step, the Boyce-Codd Normal Form.
BCNF is simply a stronger definition of 3NF. Since BCNF is higher form of 3NF, so a relation in BCNF must be in 3NF. BCNF makes no explicit reference to first and second normal form as such, nor the concept of full and transitive dependence.

 
by Dinesh Thakur Category: RDBMS

Relational Algebra is a procedural language that can be used to tell the DBMS how to build a new relation from one or more relations in the database and the Relational Calculus is a non-procedural language that can be used to formulate the definition of a relation in terms of one or more database relations.



 
by Dinesh Thakur Category: RDBMS

More precisely, the relational model is concerned with three components: Data Structure,Data Integrity,Data Manipulation

 
by Dinesh Thakur Category: RDBMS

If a system does not employ some protocol that ensures deadlock freedom, then a detection and recovery scheme must be used. An algorithm that examines the state of the system is invoked periodically to determine whether a deadlock has occurred. If one has, then the system must attempt to recover from the deadlock. To do so, the system must.



 
by Dinesh Thakur Category: RDBMS

Relational operators are classified into two types:
• Traditional Set Operators
• Special Operators

 
by Dinesh Thakur Category: RDBMS

We have already seen relational algebra is a procedural language, in which user has to write the steps or procedure to obtain the required results but in general a user should not have to be concerned with the details of how to obtain information. In relational calculus user is not concerned with the procedure to obtain the results, he/she just tell his/her requirements and the output is available without knowing the method about its retrieval.



 
by Dinesh Thakur Category: RDBMS

Designing of database is most important responsibility of the software professionals who are dealing with the database related projects. For this they follow the Design Methodology. It helps the designer to plan, manage, control, and evaluate database development projects.



 
by Dinesh Thakur Category: RDBMS

A relation is said to be in First Normal Form (lNF) if and only if every entry of the relation (the intersection of a tuple and a column) has at most a single value. In other words "a relation is in First Normal Form if and only if all underlying domains contain atomic values or single value only."

 
by Dinesh Thakur Category: RDBMS

It deals with the cost of implementing locks depending upon the space and time. Here, space refers to data structure in DBMS for each lock and time refers to handling of lock request and release.
The cost of implementing locks depends on the size of data items. There are two types of lock granularity:



 
by Dinesh Thakur Category: RDBMS

A relation R is in Third Normal Form (3NF) if and only if the following conditions are satisfied simultaneously:
1. R is already in 2NF
2. No nonprime attribute is transitively dependent on the key.
Another way of expressing the conditions for Third Normal Form is as follows:
1. R is already in 2NF
2. No nonprime attribute functionally determines any other nonprime attribute.
These two sets of conditions are equivalent.

As these two definitions of 3NF imply, the objective of transforming relations into 3NF is to remove all transitive dependencies. So, first we are going to explain the concept of transitive dependency.

 
by Dinesh Thakur Category: RDBMS

In order to understand deadlock, let us consider the following example:

 

 
by Dinesh Thakur Category: RDBMS

Dr. E.F. Codd, the founder of the relational database systems, framed twelve rules to assist a database product to qualify as relational. An RDBMS product has to satisfy at least six of the 12 rules of Codd to be accepted as a full-fledged RDBMS. There is no RDBMS package commercially available that satisfies all the 12 rules. These rules are:



 
by Dinesh Thakur Category: RDBMS

There are two approaches used in algorithms to deals with the problems of concurrency control. These are:
• Pessimistic Approach
• Optimistic Approach

 
by Dinesh Thakur Category: RDBMS

Definition of second normal form is:

A relation R is in second normal form (2NF) if and only if it is in INF and very non-key attribute is fully dependent on the primary key.

 

Page 1 of 3



About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.