Data Abstraction

Data Abstraction

It is a characteristics to show program-data independence as well as program operation independence. Infact data model is a kind of data abstraction, which hides storage and implementation detail; only provides the simple logical concepts like object (entity), their properties (attributes), their relationship etc.

Catalog:- A data-base system contains the data-base itself as well as complete definition of data-base structure and constraints. The definition (i.e. structure of each file, type and storage format of each data items and various constraints on the data) is stored in file called system catelog and the complete information of catelog is called meta-data.

Program data independence:- Generally, in the file processing system the structure of data file and access programs both are stored as a single format then the change in the structure of a file requires the change in access programs of that file. Whereas in DBMS the structures of data files is stored in the catelog and access programs are separated with these data files. So, this feature is called program data independence.

Program operation independence:- Operation on data can be defined as a part of database definitions by us in object oriented and object relational data-base. This operation (function) has two parts:-

• Interface (signature) of an operation which includes operations name and the data types of its variables(arguments).
• Implementation of the operation is specified, but this is seperated from interface and can be changed without affecting the interface.

When we want to operate on data by our application programs then these operations are called only by their names and arguments, regardless of how the operations are implemented, this is called program operation independence.

Data Model

Data model is a collection of concept that can be used to define the structure (means data types, relationship, constraints for controlling data) of a data-base as well as to achieve abstraction (hiding the detail of data storage). There are various types of data models, that we divided into three different categories:-

Object Based Data Model:- This model is used to deal data at logical and view levels. Their special features include: flexible structure capabilities and specific data constraints. It can also divided into following types:-

• Entity Relationship Model (E-R Model).
• Object Oriented Model.
• Semantic Model.
• Functional Data Model.

Record Based Data Model:- This model is used to deal data at logical and view levels, in which data-base is structured of several types of records with standard format. Their special features include: overall logical structure of data-base as well as execution details at higher level. It can also divided into following types:-

• Relational Data Model.
• Network Data Model.
• Hierarchical Data Model.

Physical Data Model:- This model is used to deal data at the lowest level (i.e. it provides concept that describes the details of how data is stored in computer). It can also divided into following types:-

• Unifying Model.
• Frame Memory Model.

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