Overview of Entities

An entity is a grouping of things with rules or data in common. An entity often represents:

• a group of people (for example, children, applicants, stakeholders),
• a group of objects (for example, textbooks, products, assets),
• a group of activities (for example, assignments, tasks), or
• a group of concepts (for example, school terms, income years).

A member of the entity group is called an entity instance. For example, if a family had two children, Sarah and Peter. Sarah would be one instance of "the child" entity and Peter would be another instance of "the child" entity.

By creating an entity to represent "the child", attributes such as the child's age can hold a different value for each child. For example, the child Sarah may be aged 6, while the child Peter may be aged 12.

Entities allow the same set of rules to be used for multiple instances of the same thing, and allow you to write rules which relate to all of those instances. For example:

• a single eligibility rule could be applied to each child in a family application,
• a requirement is satisfied if a particular number of children satisfy the eligibility rules, or

• a family payment might be payable at varying rates depending on the age and circumstances of each child in the family.

One of the challenges when modeling entity rules is deciding when entities need to be created to accurately model the source material. When deciding whether an entity is required, consider whether a particular rule, or attribute is likely to require more than one value to give effect to the source material. For further guidance on when to use entities, see Plan your project.