(relationship) and EMPLOYEES (entity) together signify a binary

(relationship) and EMPLOYEES (entity) together signify a binary relationship. A SUPPLIER (entity) SUPPLY (relationship) PARTS (entity) to PROJECT (entity) signify a ternary relationship because three entities, namely supplier, parts and projects are participating in supply relationship in any transaction. Fig. .

: Diagram showing ternary relationship between suppliers, parts and projects (iii) Role Names : Each entity type that participates in a relationship type plays a particular role in the relationship. The role name signifies the role that a participating entity of an entity type plays in each relationship instance. In PREPARED BY relationship type, EMPLOYEE plays the role of document creator and voucher plays the role of document created . (iv) Structural Constraints : The reality may impose certain constraints (or restrictions) that may limit the possible combinations of entities, participating in a given relationship set.

These are of two types : Cardinality Ratio and participation. Cardinality Ratios for binary relationship specifies the number of relationship instances that an entity can participate in. In binary relationship type, VOUCHER:EMPLOYEE is of cardinality ratio