4a.     Explain what cardinality constraints are and how they impact on database design.

 

Cardinality Constraints indicate whether the types of relationships between entities are either mandatory or optional. Mandatory Relationships indicate that the relationship MUST be maintained (e.g., a Mandatory 1:M relationship indicates that there must be one and only one on the side of the one and that there must be many on the side of the many). With respect to database design, it may indicate that certain fields may either be left null (no data need be entered)or should be designated as NOT NULL (Data must be entered).