By Martin Gogolla
This textual content provides a entire 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 information version the textual content introduces a language for the formula of constraints for you 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 energy 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 technique is that it turns into attainable to end up language houses on a legitimate mathematical basis.
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Extra info for An Extended Entity-Relationship Model: Fundamentals and Pragmatics
Iii. If t E TERM, then UNDEF(t) E FORM and free(UNDEF(t)) :-- free(t). iv. If c E CONSTRUCTION, sin C input(c), so~t E output(c), tin E TERMs,m, and to~t E TERM ..... then tin IS to~t E FORM with free(tin IS tout) := free(tin) U free(to, t). v. If f E FORM, then -~(f) E FORM and free(-~(f)) := free(f). vi. If f~, f2 E FORM, then (f~ V f2) E FORM and free((fl V f2)) :-- free(f1) U free(f2). vii. If f E FORM and d E DECL, then 3d(f) E FORM and free(3d(f)) :-(free(f)-decl(d)) U free(d). The semantics of formulas is a relation #[FORM] C FORM x ASSIGN.
5. (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.
If r ~ R A N G E , , then set(r) E RANGE,~t(,) and freeRANGE(set(r)) := free(r). The semantics of ranges is a function #[RANGE] : R A N G E x ASSIGN --~ ]~[EXPR(SORT)]. i. #[RANGE](s,~) := #[SORT](@ ii. #[RANGE](t,a) := #[TERM](t,c~). iii. #[RANGE](set(r),c~) := 9c(#[RANGE](r,a)). In addition to the ranges s E E N T T Y P E or s E R E L T Y P E known already from the simplified form of declarations, we can use any set-valued term as a range. As we shall see later, if bag- or list-valued terms were allowed in this context, then this would destroy attractive properties of our calculus.
An Extended Entity-Relationship Model: Fundamentals and Pragmatics by Martin Gogolla