March 2014 Archive


Outerjoins

An attribute of the join operator is that it is possible for certain tuples to be "dangling"; that is, they fail to match any tuple of the other relation in the common attributes. Dangling tuples do not have any trace in the result of the join, so the join may not represent the data of

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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