Database Design Quiz Week 4

A composite UID in Barker’s Notation is best defined as:

• A single attribute marked with a #.

• A combination of attributes and relationships.

• A derived attribute like totalSales.

• A subtype entity.

A fan trap occurs in an ERD when:

• A relationship is missing between two entities.

• Three entities have unresolved many-to-many relationships.

• A subtype is nested beyond three levels.

• Historical data is stored redundantly.

A recursive relationship is used to model:

• A supertype-subtype hierarchy.

• An entity linked to itself (e.g., employee-manager).

• A mandatory arc between two entities.

• A weak entity dependency.

In a multi-level UID structure, the UID of a child entity:

• Must always be a surrogate key.

• Depends on the UID of its parent entity.

• Cannot include attributes from the parent.

• Is optional.

To resolve a chasm trap, you must:

• Delete redundant attributes.

• Add a direct relationship between two entities.

• Use nested subtypes.

• Convert a composite UID to a simple UID.

Storing historical data (e.g., price changes) requires:

• Redundant attributes in the original entity.

• A new entity linked to the original entity.

• A derived attribute.

• A recursive relationship.

When modelling roles (e.g., mechanic/customer), the BEST approach is to:

• Create separate entities for each role.

• Use a supertype (e.g., PERSON) with subtypes.

• Add optional attributes to a single entity.

• Use arcs to represent exclusivity.

In a composite UID, if one attribute is NULL:

• The UID is still valid.

• The UID becomes non-unique.

• The entity instance is deleted.

• A surrogate key is automatically generated.

An arc in Barker’s Notation is used to indicate:

• A recursive relationship.

• Mutually exclusive relationships.

• A weak entity dependency.

• A hierarchical structure.

A network structure (many-to-many recursive relationship) is resolved by:

• Adding a supertype.

• Introducing an intersection entity.

• Using a composite UID.

• Deleting redundant relationships.