Re: ISSUE-66: Extended proposal for recursion

I had already made the execution order predictable: And, Or and Xor take 
an ordered rdf:List of shapes, and the engine executes them in-order. 
Where else could the order matter?

Also note that the "fatal error" is only per (recursive) constraint, 
i.e. other constraints may still be evaluated if that's desired.

Holger


On 7/10/15 3:11 PM, Peter F. Patel-Schneider wrote:
> "Throwing a fatal error whenever ..." brings in the notion of execution order,
> so I don't think that this can be counted on as "nothing [can] possibly go
> wrong" without some analysis.
>
> peter
>
>
> On 07/09/2015 09:49 PM, Holger Knublauch wrote:
>> A while ago I had suggested a solution to the recursion question that would
>> throw a fatal error ("cannot handle") whenever it encounters a recursive call
>> to sh:hasShape with the same ?node/?shape pair. The intention of this was to
>> have a conservative, minimal base line, where nothing could possibly go wrong.
>>
>> As discussed today and suggested by Arthur, it is safe to extend this policy
>> to also support the simple (but common) cases of direct recursion using
>> sh:valueShape. I have modified my algorithm so that it now returns "true" as
>> long as it stays inside the boundaries of sh:valueShape only. Any other use of
>> recursion (including negation, xor and QCRs) remains as before, i.e. it will
>> throw an error to indicate that it cannot process this request.
>>
>> Implementation detail: here, the sh:hasShape function takes another optional
>> argument ?recursionIsError which is set to true when called from within a
>> sh:NotConstraint, sh:XorConstraint etc. With this implementation, only the
>> following test cases end with a fatal error: recursive-003, 005, 006, 007, 008
>> but the others work fine, including the Polentoni example [1]
>>
>> With this I believe we can proceed with a design that generally allows
>> recursion based on sh:valueShape, and throws "cannot handle" errors for the
>> complex cases. I believe this is easy enough to explain and implement.
>>
>> Holger
>>
>> [1]
>> https://github.com/w3c/data-shapes/blob/ISSUE-62/data-shapes-test-suite/tests/features/core/manifest.ttl
>>
>>

Received on Friday, 10 July 2015 06:01:55 UTC