- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Tue, 05 May 2015 21:20:01 -0700
- To: Iovka Boneva <iovka.boneva@univ-lille1.fr>, RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 05/05/2015 03:45 PM, Iovka Boneva wrote: > Dear Peter, all, [...] > > The basic technical idea of the semantics is that nodes in a graph are > assigned zero or more shape labels and then the elements of these > assignments have to be backed up with local derivations that cover all > the outgoing edges from a node and are consonant with the shape labels > assigned to neighbouring nodes. This gets around problems with > ill-foundedness of recursive shapes. > >> There is no problem with recursion. Peter, as you already realized >> earlier, there was a problem with recursion in the initial Eric's shape >> expressions, because of the 'exclusive or' (so hidden negation) >> combined with recursion. On the other hand, I think I convinced you >> earlier that there is no problem with recursion and the 'normal' >> disjunction that we currently have in the language. Because a choice of >> only one among several (kind of 'exclusive or') is useful in the use >> cases, we added the 'one-of' operator, for which we impose a syntactic >> restriction that limits the use of recursion, while guaranteeing a >> sound semantics. The Shape Expressions 1.0 Definition http://www.w3.org/Submission/shex-defn/ is ill-founded even without negation or exclusive or. Jose's axiomatizations get around this problem but have their own problems with recursive shapes and negation (including exclusive or). I would thus say that there are indeed exhibited problems with recursion and shape recognition. These problems can be overcome in one way or another - Description Logics, for example, used one way to get around the problems and this solution is now so ingrained in the Description Logic community that there is little evidence that there once was a big debate on how to solve problems with recursive concepts in Description Logics. peter -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJVSZZxAAoJECjN6+QThfjz+mQH/jKGrOZvEJMhz5UAsKeK5JYf Try6SYH1CQYttFlOKB2Ns3lBQbqikg3CoMJyBQmW+oBRDkh4HBQvwoUglaxBzsa8 yzzij7MWNev9VmnA5q9Cho92v09p3vhHuCXh1TBIDTnsF4FyON9Z3atS9Cq4vcZn PGPg5Iy5LAW7CoU0O/NjhGzsjyJo4ZTlxCia0tZdFDmaNQHMGSvcV7B984f/fAjt kgNSN0z+v+H/M2vFhvi1HH16EEwArauQTAzP1FvwCIj4e+3z762ZY7K1ccXNpQtK 3SZiS8+YUREUceBOJn7lMjZxIzrPw4dwwdiMjldorsicGHFHsxT9/T5eVXHqwts= =BLCg -----END PGP SIGNATURE-----
Received on Wednesday, 6 May 2015 04:20:33 UTC