- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Sun, 14 Jun 2015 23:32:42 -0700
- To: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg@w3.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 06/14/2015 10:48 PM, Holger Knublauch wrote: > On 6/15/2015 15:42, Peter F. Patel-Schneider wrote: >> Changing results without negation and without disjunction requires a >> (sloppy) short-circuit evaluation on conjunction. Consider a >> conjunction where othe left branch evaluates to true and the right to >> error.. If the left branch is evaluated first and short-circuited the >> result is true. If the right branch is evaluated first then the result >> is error. > > But we assert that engines must go from left to right (just like with && > in any programming language), so the second case cannot happen. Who has so asserted this for SHACL? (It looks as if SPARQL does not enforce left-to-right evaluation for and and or, and also in other places.) > Do you have any other example of non-determinism? With recursion through negation, the order in which objects are selected during shape recognition can affect results in systems that handle loops by memoizing, even with only two values. Consider a shape like S = all R not S and a graph like V1 R V2 . V2 R V1 . Starting with V1 makes V1 in S and V2 not. Starting with V2 makes V2 in S and V1 not. Examples like this have been discussed already. Turning the different shape results into different constraint violations can be done using a qualified cardinality restriction applied to a node connected into several elements in a larger version of this loop. [...] > HTH Holger peter -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJVfnGKAAoJECjN6+QThfjzjooIALCxw3cEY6hM97R6Xs/AJAXb s+IP6oB4lyQzJ5cEkgwPVUhpRYwQA/30g0Y4h2i0d/gv7EsRxQvun/A+e8tYSA1S FVbXRB7N5gRMox6uZ3dZxwOdBK7bdL9h8yfL1VJTeK+M5Rr6HLeIPCBc3SunMOzx NgMR2w7J0tCjLQiIWadCY9MvPlgkjDYcLcLJKDo80YE7ESXlh/wV5MxUHZMNoGQ2 pQLxyFXITqj8sdFtSLcwrwDLrZMfvrmIkG6yC0iV+vkMXX9erkDv0zrH2B+BCJN+ I4nOcps2+3eU9j8Av/BEbxbJ9BhULZQmanFF3/NHfa/fSpi90caaL4qzpuPmiuM= =VZVL -----END PGP SIGNATURE-----
Received on Monday, 15 June 2015 06:33:19 UTC