Functional Dependencies

Roles in Relationships

It is possible that one entity set appears two or more times in a single relation ship. If so, we draw as many lines from the relationship to the entity set as the entity set appears in the relationship. Each line to the entity

Reasoning About Multivalued Dependencies

There are a many rules about MVD's that are similar to the rules we learned for FD's in "Rules About Functional Dependencies". For instance, MVD's obey

Nested Relations

Relations extended by point (1) of The Object-Relational Model are sometimes called "nested relations''. In the nested-relational model, we allow attributes of relations to have a type that is not atomic: particularly, a type can be a relation schema. Thus, there is a convenient,

Constraints on Relations

Relational algebra offers a means to express common constraints, such as the referential integrity constraints introduced in The Modeling of Constraints. Actually, we shall see that relational algebra provides us convenient ways to express a large variety of other constraints. Even

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