Selasa, 22 Desember 2009

RELATION DATA MODEL

DEFINITION : integrated collection of concepts, theories, axioms, contraints for description, organization, validation and interpretation of data.
USAGE : a fundamentals set of tools and methods to consistently & uniformty view, organize and tread database.

TYPE DATA MODEL :
- Reational
- Hierarchical
- Network

OBJECT-BASED MODEL :
- Entity Relationship
- Semantic
- Functional
- Object Oriented
Representation of data as an integrated collection of inter-related tables



Definition of tablesin relations data model, a tabled is viewed as a set of entities/object/record. each tabled is assigned a unique name.
A row (Called record or tuple) in a table represents an, entity, described by a set of common attributes.
Sample of relational data

An entity is a thing/something that can be identified uniquely.
A collumn in a table represents an attribute, or field that describes/characterizes an entity.

Domain of an Attribute

Domain of an attribute i (Donated D(i), is a set of all permissible value for the attribute i.
reffering to table course of figure 1:
D(credit)={x|0<6 and xEI}