- From: Arthur Ryman <arthur.ryman@gmail.com>
- Date: Tue, 23 Feb 2016 21:24:37 -0500
- To: "public-data-shapes-wg@w3.org" <public-data-shapes-wg@w3.org>
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 02:25:06 UTC