From: Axel Polleres <axel.polleres@deri.org>

Date: Mon, 27 Feb 2012 23:16:05 +0100

Cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>

Message-Id: <0D7A5BAC-4049-4BC7-9D14-747AEF8F1027@deri.org>

To: Andy Seaborne <andy.seaborne@epimorphics.com>

Date: Mon, 27 Feb 2012 23:16:05 +0100

Cc: "SPARQL Working Group" <public-rdf-dawg@w3.org>

Message-Id: <0D7A5BAC-4049-4BC7-9D14-747AEF8F1027@deri.org>

To: Andy Seaborne <andy.seaborne@epimorphics.com>

Hi Andy, Two questions for clarification: > A minimal change is a pair of new operators {*} and {+} which are the > analogous to * and +. > > {*} and {+} are counting > * and + are not (a change to 2LC). 1) So, would e.g. :p{*}/:q* mix non-counting and counting? 2) Is this meant on top or alternatively to DISTINCT() ? best, Axel On 27 Feb 2012, at 22:49, Andy Seaborne wrote: > 1/ There are two use cases for arbitrary length paths > UC1: Finding or testing for connectivity of nodes: e.g. rdfs:subClassOf* > UC2: Coping with variable structures and aggregation > > > 2/ Property paths can be expensive, notably in UC2. > > 3/ We want to leave open the possibility of path lengths > > (foaf:knows* is not a clear cut example - your LinkedIn graph is not > simple connectivity) > > 4/ PP transforms are used to define property path evaluation > leaving only ZeroLengthPath, ZeroOrMorePath, OneOrMorePath, and > NegatedPropertySet to be defined in the evaluation semantics. > > ----- > > DISTINCT is one way forward. > > ?x DISTINCT(path) ?y . > > is the pairs of (?x,?y) connected by path. > > ?x DISTINCT(path*) ?y is connectivity. > ?x path* ?y is counting as per current spec. > > ----- > > A minimal change is a pair of new operators {*} and {+} which are the > analogous to * and +. > > {*} and {+} are counting > * and + are not (a change to 2LC). > > (This is based on guessing {?length} is a future path length syntax - > see also discussion of {N,M} > > This is less than ?x DISTINCT(path) ?y > It can be "as well as". > > Roughly: the distinct * and + are achieved by changing ALP to remove the > last line "remove x from V". We need to check the edge cases still. > > It's this state management operation that controls whether the test for > termination is along the current path (counting) or whether the function > has visited the node at all. > > ----- > For {*}: > > {N,M} is untouched. > {0,*} is defined to be equivalent to {*} (i.e. still counting) > > {N,M} can be very expensive (think {0,N} in a clique of N nodes) but it > is syntax for ways to write the pattern as it would be in SPARQL 1.0 > > ?X:p{1,M} ?Y is > > ?X :p ?Y . > UNION > ?x :p ?a1 . ?a1 :p Y > UNION > ?x :p ?a1 . ?a1 :p ?a2 . ?a2 :p ?Y > ... > ?x :p ?a1 . ?a1 :p ?a2 . ?a(M-1) :p ?Y > > Andy > >Received on Monday, 27 February 2012 22:16:38 GMT

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