[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]

*Subject*: **+x/+y/+x+y**

*From*:**"Drummond Reed" <drummond.reed@cordance.net>***To*: "'OASIS - XDI TC'" <xdi@lists.oasis-open.org>*Date*: Mon, 9 Feb 2009 23:20:43 -0800

On the last telecon we discussed the set of XDI RDF statements that Markus and I concluded are inferred the XDI subject +x+y: #1) +x/$has/+y #2) +y/$is$has/+x ;inverse of #1 #3) +x/+y/+x+y #4) +x+y/$is+y/+x ;inverse of #3 #5) +y/$a/+x+y #6) +x+y/$is$a/+y ;inverse of #5 #7) +x/$has$a/+y #8) +y/$is$has$a/+x ;inverse of #7 At the end of the telecon, Giovanni asked "Is #3 above, i.e., +x/+y/+x+y, really an inference from +x+y, or does that follow from a specific graph notation?" I had the action item to pen an answer. My answer is that yes, since the XDI subject +x+y represents the XDI metagraph statement +x/$has/+y, then it infers all 7 of the other statements above, irrespective of any particular graph notation. In fact, the RDF relationship represented by +x+y has a direct RDF graph that doesn't require any of the XDI metagraph predicates toe express. In ASCII art (where [] is a node and --- label ---> is an arc): [+x] --- +y ---> [+x+y] Note that all three XRIs are needed to capture this graph in standard RDF. In other words, the $has statement +x/$has/+y does not constrain the subject +x to just having a singleton predicate +y. +x may in fact have any number of predicates +y (if so, that means +x/$has$a/+y). However the statement +x/$has/+y is the assertion that +x has EXACTLY ONE +y predicate AND that the object of that predicate MUST have the identifier +x+y. Another way to put it is that, in contrast to a $has$a statement, a $has statement is a way of expressing the English article, "the". So while +x/$has$a/+y is a way of referring to "a" predicate +y on +x (i.e., the class of all +y that are predicates on +x), +x/$has/+y is a way of referring to THE (exactly one) +y that serves as a unique path to the object node, which by definition has the path (address) +x+y. (Like any XDI subject, it can also have other XRI synonyms, but this one is know a priori.) Hope this helps, =Drummond

**Follow-Ups**:**Re: [xdi] +x/+y/+x+y***From:*Giovanni Bartolomeo <giovanni.bartolomeo@uniroma2.it>

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]