Create a running example for the rules description section

[afs]

[liviorobaldo]

I see there are already some examples in SHACL 1.2 Rules, involving fathers, mothers, children, and descendants.

These examples are simple and intuitive enough for everyone to understand, so I would build on them and use a single running example throughout the document.

In particular:

• 3.1 Basic Patterns

  The example already there is fine: RULE { ?x :childOf ?y } WHERE { ?y :fatherOf ?x }, etc.

• 3.2 Recursion

  The example already there is fine: RULE { ?x :descendedFrom ?y } WHERE { ?x :childOf ?y }, etc.

• 3.3 Filtering

  I would replace the :largeTown example with one based on the same family scenario. For example:

  RULE { ?y1 :siblingOf ?y2 . ?y2 :siblingOf ?y1 } WHERE { ?x :childOf ?y1 . ?x :childOf ?y2 . FILTER(?y1 != ?y2) }

  This example also shows that multiple triples can appear in the rule head, whereas the previous examples only have a single triple in the head.

  After this example, in this section I would also add:

  RULE { ?y1 :isOlderThan ?y2 } WHERE { ?y1 :siblingOf ?y2 . ?y1 :hasAge ?a1 . ?y2 :hasAge ?a2 . FILTER(?a1 > ?a2) }

  This rule will fire after the previous one, because the two individuals must first be inferred to be siblings. It also shows that FILTER can be applied to datatype values. In the previous example, FILTER is only used to prevent the property :siblingOf from being reflexive.

• 3.4 Negation

  Again, I would replace the :Place/:population example with one based on the same family scenario. For instance:

  RULE { ?x :motherOf ?y } WHERE { ?x :parentOf ?y . NOT { ?x :fatherOf ?y } }

  RULE { ?x :fatherOf ?y } WHERE { ?x :parentOf ?y . NOT { ?x :motherOf ?y } }

  If ?x is a parent of ?y and ?x is not ?y's father, then ?x is the mother. Conversely, if ?x is not ?y's mother, then ?x is the father.

• 3.5 Assignment and Creating RDF Terms

  I must admit that the existing example (converting miles into kilometres) is quite clear, so perhaps we can simply keep it, even if it is not connected to the family scenario. The only examples involving fathers, children, etc. that I can think of would require aggregates.