- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Wed, 24 Feb 2016 06:12:26 -0800
- To: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg@w3.org
I think that the way to do this would be to not have recursion as a part of SHACL. As far as I know, W3C recommendations are generally open, in that they allow for implementations to extend the language but still be advertised as compliant. (Some other standards do not allow this. I think that ECMAScript falls into this category.) This would be much more like the situation in OWL, where a particular language was recommended but many reasoning implementations handled a larger language. peter On 02/23/2016 10:33 PM, Holger Knublauch wrote: > Could we simply say "handling of recursion is left to the discretion of the > implementations" and close all related tickets? This way, we can basically > outsource the problem to the open source and research communities and move on. > The description logics community also made progress over time, after the OWL > standards were published. > > Engines that have larger coverage get bonus points, but implementations that > just want to cover basic SHACL compliance don't have to worry about all the > details. We simply wouldn't define test cases that use recursion. The ShEx > people can support it if they like. > > Holger > > > On 24/02/2016 12:24, Arthur Ryman wrote: >> I've had this action for a while but have not been able to make >> progress due to other commitments. I'd like to summarize my thoughts >> here and will then close the action. >> >> Recursion arises when the evaluation of a shape at a node depends >> directly or indirectly on itself. If we allow this situation to occur, >> then we are obligated to define what it means. >> >> I believe SHACL has well-founded semantics in the absence of >> recursion. That is our starting point. Any new semantics that allows >> recursion must agree with the current semantics in the absence of >> recursion. >> >> The SHACL specification currently prohibits recursion. However, there >> is some motivation for allowing limited forms of recursion. See [1]. >> >> I believe we can assign a well-founded sematics to recursion that does >> not involve either negation or disjunction. I wrote a Z specification >> that defined the semantics of this type of recursion as it appeared in >> OSLC Resource Shapes. [2] I had hoped to apply that approach to the >> current SHACL spec, but have not found the time. I still believe this >> approach is feasible. >> >> [1] >> https://www.w3.org/2014/data-shapes/wiki/ISSUE-66:_SHACL_spec_ill-founded_due_to_non-convergence_on_data_loops >> >> >> [2] http://arxiv.org/abs/1505.04972 >> >> -- Arthur >> > >
Received on Wednesday, 24 February 2016 14:12:56 UTC