Alternative Modeling Conventions

Diagram Conventions

ER modeling concepts vary; may:
- Allow relationships between three or more entities
- Decompose a complex model into a group of related entities, called a subject area
- Refer to strong entities as independent and weak entities as dependent
Are standardized modeling conventions:
- Unified Modeling Language (UML)
  - is commonly used for software development
  - Software data structures are similar to database structures,
    - so UML includes ER conventions
- Information DEFinition version 1X (IDEF1X)
  - popular due to adoption by department of defense
- Chen notation
  - is not standardized but often appears in literature and tools
differences between conventions are stylistic rather than substantial
- does not usually affect the resulting database design

An intangible entity is documented in the data model, but not tracked with data in the database.

In an ER diagram, intangible entities are distinguished with special notation, such as a dashed rectangle or distinct color