the real world consists of entities and relationships.
Way of modeling data:
- similar things are called entity
- with relationship
As data modeling rules apply to all sort of domain, this section threats data modeling on a logical level and not on a implementation level.
For instance, a primary key can be represented/enforced:
A Data model graph formally define:
There is two world view:
- and an event-oriented
There is not a right or wrong way of doing things as:
- design decision involves trade-offs between:
- against reduction of data duplicate and design complexity.
- every data model is meant to evolve. See Gay marriage: the database engineering perspective
In a RDBMS,
- and the foreign keys, the relationship
- and the relationship can be:
- structural (external variables) - ie data based
- or functional (dependency) - ie function based