Combining Relations

Often, the relations that we get from converting entity sets and relationships to relations are not the best possible choice of relations for the given data. One ordinary situation occurs when there

An Object-Oriented Approach

Another strategy for converting isa-hierarchies to relations is to enumerate all the possible subtrees of the hierarchy. For each, create one relation that represents entities that have

Functional Dependencies

"From E/R Diagrams to Relational Designs" and "Converting Subclass Structures to Relations" showed us how to convert E/R designs into relational schemas. It is also possible for database designers to produce relational schemas directly from application requirements,

The Transitive Rule

The transitive rule lets us cascade two FD's. ● If A1A2 . . . An → B1B2 . . . Bm and B1B2 . . . Bm → C1C2 . . . Ck hold in relation R, then A1A2 . . . An → C1C2 . . . Ck also holds in R.

Semistructured Data

The semistructured-data model plays an important role in database systems: 1. It serves as a model appropriate for integration of databases, that is, for describing the data included in two or more databases that include similar data with different schemas.

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