Database Characteristics | DBMS | Database Management Systems

DATABASE CHARACTERISTICS: 

The main characteristics that distinguish the database approach from the traditional approach of programming with files are given below: 

1. SELF-DESCRIPTION: 

The database system contains not only the database itself but also a complete definition or description of the database structure and constraints.

This definition is stored in the system catalog,Which contains information such as the structure of each file,the type and storage format of each data item,and various constraints on the data.

The information stored in the catalog is called meta-data,and it describes the structure of the primary database.

The catalog is used by the DBMS software and also by database users who need information about the database structure. 

2. INSULATION BETWEEN PROGRAMS AND DATA: 

In traditional file processing,the structure of the data files accessed by an application is "hard-coded" in its source code.

If,for some reason,we decide to change the structure of the data(e.g., by adding the first two digit to the year field.),every application in which a description of that file's structure is hard-coded must be changed!

In contrast,database management systems access programs,in most cases,do not require such changes,because the structure of the data is described in the system catalog separately from the programs that access it and those programs consult the catalog in order to ascertain the structure of the data so that they interpret that data properly.

In other words,the database management systems provides a conceptual or logical view of the data to application programs,so that the underlying implementation may be changed without the program being modified.This is referred to as program data independence.

The characteristic that allows program data independence and program operation independence is called data abstraction.

A database management systems provides users with a conceptual representation of data that does not include many of the details of how the data is stored or how the operations are implemented,Informally,a data model is a type of data abstract that is used to provide this conceptual representation.

The data model uses logical concepts,such as objects,their properties,and their inter relationships,that may be easier for most users to understand that computer storage concepts.

Hence,the data model hides storage and implementation details that are not interest to most database users.

For example, consider that the internal implementation of a file may be defined by its record length,the number of characters in each record,and each data item may be specified by its starting byte with in a record and its length in bytes.

A typical database user is not concerned with the location of each data item with in a record or its length;rather when a reference is made to name of student,the correct value is returned instead of implementation details.This is called as data abstraction.

In object-oriented and object-relational databases,abstraction includes not only the data structure but also the operations on the data.

For example,an operation calculate_total can be applied to a student object to calculate the total marks.Such operations can be invoked by the user queries or program without the user knowing the details of how many are internally implemented.

In this way sense,an abstraction of the mini world activity is made available to the user as an abstract operation.

3. Multiple views of data:

A view may be a subset of the database.A database typically has many users,each of whom may require a different perspective or view of the database.

A multi user database management systems whose users have a variety of applications must provide facilities for defining multiple views.

For example,in student database management system,the accountant cannot view student's attendance record and teacher cannot view fees record.

A good database management systems has facilities for defining multiple views.This is not only convenient for users,but also addresses security issue of data access.

4. Data sharing and multi-user transaction processing: 

A multi user database management systems must allow multiple users to access the database at the same time.

This is essential is data for multiple applications is to be integrated and maintained in a single database.

The database management systems must include concurrency control software to ensure that several users typing to update the same data do so in a controlled manner so that the result of the updates is correct.

A fundamental role of multi user database management  systems software is to ensure that concurrent transactions operate correctly.

For example,when several railway reservation clerks try to assign a seat,the database management systems should ensure that each seat can be accessed by only one clerk at a time for assignment to a passenger.

These types of applications are generally called On-line transaction processing applications.