Explains the connection, fan and chasm traps

K-569 · Knowledge knobit · Activity: Derive the logical data model · Competence: Data modelling

How a path of relationships can state a fact that was never recorded, lose a question, or drop instances.

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What it looks like in practice

Expected result: How a path of relationships can state a fact that was never recorded, lose a question, or drop instances

How it is assessed: Names the trap on sample paths of two relationships and what each lets a reader wrongly conclude

Related knobits

Builds on

• K-567 Explains relationship cardinality and optionality

Needed for

• K-523 Recognises a connection trap
• K-524 Recognises a fan trap
• K-525 Recognises a chasm trap
• K-628 Recognises a nullable foreign key on a reporting join path

All 56 knobits of Derive the logical data model.

Source: Normalisation theory and relational design (Codd, Fagin, Date), as used by the stage 5 reference and review checklist