Download e-book for iPad: An Extended Entity-Relationship Model: Fundamentals and by Martin Gogolla

By Martin Gogolla

ISBN-10: 0387576487

ISBN-13: 9780387576480

ISBN-10: 3540576487

ISBN-13: 9783540576488

This textual content offers a accomplished advent to a longer Entity-Relationship version either on a conceptual and on a proper, mathematicallevel. as well as the primitives given by way of the knowledge version the textual content introduces a language for the formula of constraints to be able to limit database states to constant ones. The textual content explains an implementation of the technique selected within the common sense programing language PROLOG and discusses during this context the computational strength of the proposedcalculus. The prolonged Entity-Relationship calculus is used to outline the which means of the relational question language SQL. a pleasant function of the procedure is that it turns into attainable to turn out language houses on a legitimate mathematical basis.

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Extra resources for An Extended Entity-Relationship Model: Fundamentals and Pragmatics

Example text

Since this function is injective, every output entity corresponds to exactly one input entity. But an input entity need not appear in an output type at all, because the function is not required to be surjective. The injective function #[CONSTRUCTION](c) is a technical requirement, because we want all entity types to be disjoint (with the exception of • Generally speaking, it is true that a set inclusion S c T induces an injective function f : S --+ T; on the other hand, if we have an injective function f : S -+ T, this induces the set inclusion f(S) C T.

SCHEMATA 29 {partition-person, specialize-to-port, specialize-to-capital, special-vehicles} with input and output specified below. 14: Type constructions as partitionings. 14 represents a partitioning of the input type PERSON into the entity types MALE and FEMALE. Generally speaking, this situation allows entities of type PERSON which are neither MALE nor FEMALE. If one wants to exclude this, an additional constraint has to be specified. 29 in the section on integrity constraints. 15: Type constructions as specializations.

We shall define the textual and graphical representations of the schemas. 15 Example: Extended Entity-Relationship schema Let us now consider the simple geographic database application already mentioned, in which countries, towns, and special kinds of bodies of water are described. The following schema definition (denoted in a linear way) belongs to our geo-scientific application. SCHEMA ENTTYPES CTW-WORLD COUNTRY ATTRIBUTES COMPONENTS RELTYPES TOWN ATTRIBUTES RIVER ATTRIBUTES LAKE ATTRIBUTES SEA ATTRIBUTES WATERS PERSON ATTRIBUTES ATTRIBUTES lies-in lies-at PARTICIPANTS PARTICIPANTS ATTRIBUTES flows-through PARTICIPANTS ATTRIBUTES flows-into PARTICIPANTS is-mayor-of PARTICIPANTS CONSTRUCTIONS are INPUT OUTPUT cname : string area : regions cpopulation : int government : forms h e a d : PERSON ministers : LIST(PERSON) tname : string tgeo : circle tpopulation : int rname : string rgeo : lines iname : string igeo : circle shame : string sgeo : polygon wname : string pname : string addr : LIST(address) age : int COUNTRY, TOWN TOWN, RIVER distance : real COUNTRY.

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An Extended Entity-Relationship Model: Fundamentals and Pragmatics by Martin Gogolla


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