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Monday, 11 January 2016

Entity

What is Entity?

It is a thing of significance about which information need be known .
An Entity is a grouping of things with rules or data.
An entity represents group of similar things(children,subjects,animals etc) but it can also represents group of objects(eg: text books), activities(homework) or concepts(eg: school terms).

Entity Types:

Entities are two types:
1. Regular Entities
2. Global Entities

Regular Entity:
An entity have zero or more entity instances.
example car in a vehicle.
Children in a family
Using entities you can apply the same rules, or collect same data for multiple instance of that entity instances.

Global Entity:

Not all information relevant to your rules may belong to particular entity.
Oracle policy modeling has a global entity which acts as catch all information that does not belonging to any another entity.
For example: Sun shining is a global attribute and that does not belonging to the entity "the family" "the child" etc.

The global entity is the default location of attributes. If you do not create entities in your rule base, or if you create an attribute which does not belong to another entity, the attribute will be stored in the global entity.

The following diagram shows how instances of a child in a family situation have entity attributes: