Re: thisiness

On Fri, Mar 25, 2011 at 7:36 AM, Nathan <nathan@webr3.org> wrote:

We have the term "blank node identifiers" which leads many to believe that
> the identifier names the blank node, but there is no scope for that name, so
> they are non-rigid designators. The problem is that now often many see
> certain sets of triples as being associated with a name somehow  (as in
> sparql, the ?g, and linked data, the <uri> you GET) which gives a scope for
> the name, and thus the expectation is that blank node identifiers are rigid
> designators within the scope of that name. (As in, a name which acts as a
> namespace and defines a universe within which blank nodes can be both
> quantified and identified/named).
>
> Blank nodes are pretty much existentially bound variables with a quantifier
> whose scope is the entire graph, so when you have a name for two graphs and
> the name is the same, it follows that they are thought of as bound variables
> rather than free variables.
>

This is where I think the concept of indexicals is useful, at least for
expository purposes.  All natural languages (so far as I know) have
indexicals; they don't need to be explained, they would never be confused
with proper or common names, and by the very fact that they are indexical
they are never be taken as globals.  To borrow from the current thread on
blank nodes:

<foaf:knows>
  <foaf:Person>
   <foaf:nick>friend1</foaf:nick>
   <foaf:weblog rdf:resource="..."/>
  </foaf:Person>
 </foaf:knows>

can easily be understood to say "... knows this person (who is characterized
by these properties: ...)"  Most programmers these days have used a language
that includes a keyword like "this" or "self" that has essentially the same
indexical meaning.  An indexical has the additional advantage of eliminating
quantification; and whereas everybody understands "there exists x such
that", I would hazard a guess that lots of people who might use RDF are not
familiar with the terminology of quantification, so "blank node identifiers
can be thought of as existentially quantified variables" will leave them in
the dark.  Even if not, add in model theory and what you have is actually
pretty complicated.  Maybe not rocket science, but much more complex than
"this".

Besides, I like "thisiness", and it wouldn't hurt the semantic web community
to lighten up a bit, if you know what I mean. ;)

-gregg