Simple predicates

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Simple predicates

Simple predicates are always binary because they refer to graphs. Simple predicates contain patterns or variables as arguments. Predicate names must exist as the name of a object field in the data model. Thus a predicate in a rule test or rule transformation refers to

a field which has the type of a graph functor call (graph field)
a field which has the type of a set/list functor call (set field)
a field which has the type of a simple domain (non-graph) (pointer field).

The predicate

$\begin{examplefoot}p(X,Y) \end{examplefoot}$

is true if the object .Y. is contained in the set |X.p|. Also (in the generated code) the predicate p(X,Y) delivers all objects Y which are linked under field (or graph) p to object X.

Alternative notations for the predicate are:

$\begin{examplefoot}Y IN X.p // variable in neighbor set of node under relation p Y p X // infix notation \end{examplefoot}$

Uwe Assmann
1998-12-22