By Martin Gogolla
This textual content offers a complete creation to a longer Entity-Relationship version either on a conceptual and on a proper, mathematicallevel. as well as the primitives given via the knowledge version the textual content introduces a language for the formula of constraints on the way to limit database states to constant ones. The textual content explains an implementation of the technique selected within the good judgment programing language PROLOG and discusses during this context the computational strength of the proposedcalculus. The prolonged Entity-Relationship calculus is used to outline the that means of the relational question language SQL. a pleasant function of the method is that it turns into attainable to turn out language homes on a legitimate mathematical basis.
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Additional resources for An Extended Entity-Relationship Model: Fundamentals and Pragmatics
SORT = DATA U ENTTYPE (J RELTYPE If we now extend the notions of operations (OPNS) and predicates (PRED) introduced for data signatures to sort expressions and extended Entity-Relationship schemas the following notations are the result: OPNSEER ---- ATTRIBUTE (2 COMPONENT PREDEER = RELTYPE All operations and predicates are now concentrated to OPNS = OPNSDs U OPNSEER U OPNS(SORT) SECTION 3B. PRELIMINARIES 39 P R E D = PREDDs U PREDEER U PRED(SORT) ~[SORT], ~ [ O P N S ~ R ] , #[PREDEE,], #[OPNS], and #[PRED], are determined by the corresponding #'s on the right-hand side.
We have arbitrary bags, and sets can be derived from bags by applying the function BTS converting bags to sets. 1 Notation: SORT, OPNS, and PRED Before discussing the extended Entity-Relationship calculus in more detail, we introduce some abbreviations. Let an extended Entity-Relationship schema EER(DS) be given. SORT refers to the union of all data, entity, and relationship sorts. SORT = DATA U ENTTYPE (J RELTYPE If we now extend the notions of operations (OPNS) and predicates (PRED) introduced for data signatures to sort expressions and extended Entity-Relationship schemas the following notations are the result: OPNSEER ---- ATTRIBUTE (2 COMPONENT PREDEER = RELTYPE All operations and predicates are now concentrated to OPNS = OPNSDs U OPNSEER U OPNS(SORT) SECTION 3B.
WATERS(r) is a term of sort W A T E R S having the single free variable r. This term evaluates for a given a to the water corresponding to the river assigned to r by a. Indeed, we have assumed every river to be also a water (by an additional constraint). The above is not a correct term in the calculus of [Hohg0] because it does not allow this form of conversion. 4. RIVER(w) is a term of sort R I V E R having the single free variable w. This term evaluates to the river t h a t corresponds to the water assigned to w by a.
An Extended Entity-Relationship Model: Fundamentals and Pragmatics by Martin Gogolla