- From: Pat Hayes <phayes@ihmc.us>
- Date: Thu, 1 Jul 2004 11:41:15 -0500
- To: "Yuzhong Qu" <yzqu@seu.edu.cn>
- Cc: "Jeremy Carroll" <jjc@hpl.hp.com>, "www-archive" <www-archive@w3.org>
>Let's think about the abstract syntax of Named Graphs. > >A set of Named Graphs is a 5-tuple <N,V,U,B,L>, where >U is a set of URIrefs; >L is a set of literals (both plain and typed); >B is a set of Œblankšnodes; >U, B and L are pairwise disjoint; >V is the union of U, B,and L. > >Let G be the set of all subset of the cartesian product of V,U and V. > >Suppose g is an element of G, let Nodes(g)={v in >V | there exists a t in g such that p1(t)=v or >p2(t)=v or p3(t)=v }. > >(Note: p1, p2 and p3 are projections in normal sense) > >It's obvious that the set of bank nodes in g, >written by BlankNodes(g), is the intersection of >B and Nodes(g). > >There is an equivalent relation on G,written by NameBlanked, such that > >g1 NameBlanked g2 iff g1 and g2 differ only in >the identity of their blank nodes. > >Let RdfG be G/NameBlanked. > >Two alternatives for the definition of N: > >1) N is a partial function from U to RdfG. > > (As Pat pointed out in a previous thread) This >makes it mathematically impossible for two >graphs to 'share' a blank node. So, no extra >constraint is needed to prevent blank nodes >being shared between different "graphs" named in >N. > >2) N is a partial function from U to G satisfying the following constraint: > > Suppose g1 = N(n1) and g2 = N(n2), if n1 != n2 then > > The intersection of BlankNodes(g1) with BlankNodes(g2) is empty. > > (But it 's still possible to have that g1 >NameBlanked g2 i.e. they are essentially the >same rdf graph) > > > I prefer the first one. Which one do you prefer? For myself, I prefer to not go into this level of detail. I don't think its necessary: the basic concept of a bound variable is well known and its properties are well understood: there is no new mathematical insight to be had by re-inventing this wheel. Purely from a practical point of view there is nothing to be gained by describing abstract syntax at this level of mathematical depth. And from a purely pedagogic point of view, most readers of the document don't care about abstract syntax anyway. All that said, I prefer the first one :-) Pat > > Any comment is welcome! > > > >Yuzhong Qu > > > -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Thursday, 1 July 2004 12:41:12 UTC