By Martin Gogolla
This textual content offers a accomplished 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 to be able to limit database states to constant ones. The textual content explains an implementation of the strategy 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 that means of the relational question language SQL. a pleasant characteristic of the procedure is that it turns into attainable to end up language homes on a valid mathematical basis.
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Additional resources for An Extended Entity-Relationship Model: Fundamentals and Pragmatics
F:government(c)) is not a correct declaration since government(c) is not a set-valued term and consequently not a correct range. The intended formulation is the following declaration. 6. (f:BTS-[ government(c) I (c:COUNTRY) ]-) is a declaration of variable f without free variables. The variable f is bound independently of any assignment to the forms of government of each country. 7. (a:LTS(addr(p));(p:LTS(ministers(c)))) is a declaration of the variables a and p with the single free variable c.
EXTENDED ENTITY-RELATIONSHIP CALCULUS -[ pname(p) I (p : PERSON) A 3 (c : COUNTRY) (cname(c) = 'Italy' A 3 (t : TOWN) (is-mayor-of(p,t) A lies-in(c,t) ) ) l expresses the query "Give me the names of the mayors of Italian towns". The result of this query is a bag (or multiset) retaining multiple names, if two mayors have the same name. The above terms will always have the form -[
Its elements are called type constructions. A type construction c may be regarded as a re-arrangement of input entities. Starting with non-constructed or already defined entity types in input(c), the new entity types in output(c) can now be constructed. 10, not to mention its general form. Although all the entity types we have introduced are by definition disjoint, the constructed entity types may be considered as a new classification of the entities in the input types. , #[ENTTYPE](ik), SECTION 2D.
An Extended Entity-Relationship Model: Fundamentals and Pragmatics by Martin Gogolla