IB/Group 4/Computer Science/Databases/The relational database model

Database management system (DBMS) and relational database management system (RDBMS) DBMS A database management system (DBMS) is system software for creating and managing databases. The DBMS provides users and programmers with a systematic way to create, retrieve, update and manage data. RDBMS

A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. The data in an RDBMS is stored in database objects which are called as tables. Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY. A record is also called as a row of data is each individual entry that exists in a table. A column is a vertical entity in a table that contains all information associated with a specific field in a table.

Outline the functions and tools of a DBMS

The functions are:

1. It Organizes Data

2. It integrates Data

3. It Separates Data

4. It Controls Data

5. It Retrieves Data

6. It Protects Data.

1. Data are organized or structured according to the specifications of the data definition language.
The database administrator introduces these specifications at the time the database is established, and may be reintroduced as the data base configuration changes. Data are organized in the manner most suitable to each application.

==== 2. Data are interrelated or linked together at the element (named field of data) level and can, therefore, be assembled in many combinations during execution of a particular application program. The data base management system is the vehicle used to collect, combine, and return a portion of the available data to the user. ====

==== 3. It Separates Data:A data base management system serves as a filter between application programs and their associated data. It separates application logic from the input/output logic needed to calculate addresses, follow chains or links, block/unblock data, locate records, and select data elements. ====

4. It Controls Data:
A data base management system appears to an application programmer to be an extension of the operating system software. As it receives data storage requests from host programs, it controls how and where data are physically stored. On data retrievals, it locates and returns requested elements of data to the programs.

5. A record of data can be obtained via a data base management system:
(1) Serially (in its physically stored sequence),

(2) Sequentially, according to the value of a user-specified key,

(3) Randomly by key,

(4) Randomly by address, and

(5) By structural link.

All or any portion of the data record can be returned to the user.

6. A database management system protects and secures both the content of a data base and the relationships of data elements.
"Data are protected against access by unauthorized users, physical damage, operating system failure, simultaneous updating, and certain interruptions initiated by a host program."ACCESS CONTROL Authorization Authentication

data locking is locking the variable which is required by you and using it shared and exclusive lock 2phase locking

Define the term schema- A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied on the data. A database schema defines its entities and the relationship among them.