Property paths

With KR version 1.4.11 basic support for SPARQL 1.1 property paths was added to the pattern-based query language. As of writing this has been tested on sesame 2.6.8 and 2.6.10 in-memory triple stores. And only the * + and ? and sequential operators have been verified. More tests to come.

Standard SPARQL property path syntax is the following:

SPARQL       clj                 definition
-------------------------------------------
uri          symbol              A URI or a prefixed name. A path of length one.
^elt         (:inverse elt)      Inverse path (object to subject).
(elt)                            A group path elt, brackets control precedence.
elt1 / elt2  (elt1 elt2 ...)     A sequence path of elt1, followed by elt2
elt1 ^ elt2                      Shorthand for elt1 / ^elt2, that is elt1 followed by the inverse of elt2.
elt1 | elt2  (:or elt1 elt2 ...) A alternative path of elt1, or elt2 (all possibilities are tried).
elt*         [elt *]             A path of zero or more occurrences of elt.
elt+         [elt +]             A path of one or more occurrences of elt.
elt?         [elt ?]             A path of zero or one elt.
elt{n,m}     [elt n m]           A path between n and m occurrences of elt.
elt{n}       [elt n]             Exactly n occurrences of elt. A fixed length path.
elt{n,}      [elt n nil]         n or more occurrences of elt.
elt{,n}      [elt nil n]         Between 0 and n occurrences of elt.

(elt) is implicit

(elt1 ^ elt2) shorthand is unsupported use (elt1 (:inverse elt2))

examples:

[rdfs:subClassOf *]

([rdf:rest *] rdf:first)