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

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

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 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

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

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

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.



 

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