Re: is there an implementation of Shape Expressions that correctly handles recursive shapes?

* Peter F. Patel-Schneider <pfpschneider@gmail.com> [2015-03-20 06:54-0700]
> I have been looking over recursive shapes in Shape Expressions.   It appears
> to me that two of the three definitions for Shape Expressions are
> ill-founded on recursive shapes.
> 
> I have also been trying to test out implementations of recursive shapes in
> Shape Expressions.  There are five implementations of Shape Expressions
> listed on http://www.w3.org/2001/sw/wiki/ShEx
> 
> Of these five
> the section on Fancy ShEx Demo has links to three online tools of which the
> ShEx Demo appears to be the one to use to check out how Shape Expressions work,
> the link for JSShexTest puts up a bare-bones online tool,
> the link for RDFShape does not produce any result,
> the link to ShExcala produces a page that points to RDFShape as its online
> tool, and
> the link to Haws produces a 404 error.
> 
> I tried the following example of a recursive shape in all the ways that I
> could think of in the online tools:
> 
> 
> SCHEMA:
> 
> PREFIX ex: <http://ex.example/#>
> start = <S>
> <S> { ex:p @<T>* }
> <T> { ( ex:q @<Z> | ex:r @<T> ) }
> <Z> { }
> 
> DATA:
> 
> PREFIX ex: <http://ex.example/#>
> ex:a ex:p ex:b .
> ex:a ex:p ex:c .
> ex:b ex:q ex:z .
> ex:c ex:q ex:z .
> ex:b ex:r ex:c .
> ex:c ex:r ex:b .
> 
> ShEx Demo (http://www.w3.org/2013/ShEx/FancyShExDemo) appears to go into an
> infinite loop on this input.

Interesting, what browser were you using? I wonder if I need to monkey
around with patching Promises. I can check that by sticking a
synchronous (doesn't use the Promises lib) in w3.org date space. 

The attached recursiveShEx.png shows what I see with a local checkout
of the synchronous ShEx. The '|' operator is exclusive (or exactlyOne)
so the pattern failed trivially. I changed the data so that only one
disjunct matched:

  PREFIX ex: <http://ex.example/#>
  ex:a ex:p ex:b .
  ex:a ex:p ex:c .
  #ex:b ex:q ex:z .
  #ex:c ex:q ex:z .
  ex:b ex:r ex:c .
  ex:c ex:r ex:b .

and saw that ex:a matched with ex:b and ex:c matching <T>:

  PASS {
    ex:p @<T>* matched by ex:a ex:p ex:b .
      PASS {
        ex:r @<T> matched by ex:b ex:r ex:c .
          PASS {
            ex:r @<T> matched by ex:c ex:r ex:b .
              PASS {
  
              }
          }
      }
    ex:p @<T>* matched by ex:a ex:p ex:c .
      PASS {
        ex:r @<T> matched by ex:c ex:r ex:b .
          PASS {
  
          }
      }
  }
  No remaining triples.


> JSShexTest (http://www.jessevandam.nl/) very quickly produces
> Shex validation: Succes
> Result: FAIL
> which I read to mean that the validation failed, as expected.  However, I
> was not sure so I dug further.  The description of JSShexTest is supposed to
> be in http://www.w3.org/2001/sw/wiki/ValidationCode.   That page gives or as
> an inclusive or and not the exclusive or of Shape Expressions.  Under this
> reading of or, it appears to me that the result should be a success, but the
> documentation is too spotty for me to be sure of this.
> 
> 
> Is there an implementation of Shape Expressions that correctly handles
> recursive shapes?
> 
> 
> 
> peter
> 

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-ericP

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