IB Computer Science Topic A3.2.2: Constructing Entity Relationship Diagrams Key Definitions

The maximum number of instances of one entity that can be linked to a single instance of another entity, which is either one or many. It is read separately for each end of a relationship line, giving the shapes 1:1, 1:N and M:N.

A diagram of a database design that shows each entity, the attributes it stores, and the relationships between entities, with the cardinality and modality of every relationship marked on the line.

An entity placed between two entities to resolve a many-to-many relationship, replacing it with two one-to-many relationships. It becomes a junction table holding one row per pairing, keyed on the two foreign keys together.

The minimum number of instances of one entity that must take part in a relationship, which is either zero (optional) or one (mandatory). Also called optionality.