consists of sets of entities and set of relationships between those entities.
entity ==> set of attributes
relationship ==> an association between several entities
note: a function that an entity plays in a relationship is called its role
relationship's attributes are called descriptive attributes
mapping cardinalities : better explained in korth
weak entity sets : entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key. The foreign key is typically a primary key of an entity it is related to.
a weak entity set is indicated by a bold rectangle (the entity) connected by a bold type arrow to a bold diamond (the relationship). This type of relationship is called an identifying relationship
No comments:
Post a Comment