Stage 5: Derive the logical data model
Knobit of Data modelling · K-536 · Skill
Introduces subtypes for attributes applying to only some instances
What it means
Replaces optional attributes that are optional only because they do not apply to some instances with subtypes, so a null no longer means two things.
How it is assessed
Each attribute sits on the subtype it applies to and can be mandatory there; the exclusivity is written down
Builds on
- Explains supertype and subtype constraintsK-566 · Knowledge
Needed by
- None