On Jun 1, 2007, at 1:24 PM, Bijan Parsia wrote:
Even though I'm not keen on specifying the extra triples in the
query I'm not sure this warrants ad-hoc extensions to a standard.
Well, it was more of a use case. I'm thinking about syntactic sugar
for sparql as a whole and this seems to be an important case.
I'd also prefer a general macro mechanism (no surprise). For example
more annoying than the labels in the queries are the verbose
expressions for restrictions and other owl class expressions that I
have to write. But really I want to be able to encapsulate arbitrary
sized portions of queries and let people write relatively simple
expressions for useful queries.
I've been working with Jonathan a bit about this, so maybe he can
chime in with what his ideas. Also, the Virtuoso folks have offered
to prototype the macro mechanism if we come up with a spec, so we're
going to try to get something in the next few weeks for them.
I can, of course, do lisp macro expansion in LSW - I've done this
before for other query systems, but haven't done so for SPARQL yet
mostly because I've been presenting it and want everything to be
vanilla, and without extra requirements for running.
Here are two kinds of ideas for macros in SPARQL.
1) Templating: You define a template with some blanks to substitute.
"invocation" of the macro takes the arguments to it and replaces the
macro call in the query with the filled in template.
2) Full programming language generation: You assume that there is a
javascript interpreter embedded in the query parser. A macro
invocation is a javascript function call that generates a replacement
for itself (either as some sort of datastructure that is rendered
into sparql, or, in a pinch, as text). Javascript is chosen because
it is easy to embed and well known in the communities that we want to
use this stuff.
Both of these proposals annoy Jonathan to a certain extent. Hopefully
they will annoy him enough to cough up a worked out counterproposal :)
BTW, In both cases I would expect that there could be an extensible
set of such macros that live in the triple store itself, and that
would grow over time and easily be shared i.e. they would have an rdf
representation of some sort.
-Alan
