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More definition questions/suggestions

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Mon, 4 Apr 2005 16:16:47 -0400
Message-Id: <26c40e9d64a227dd74f316161d7b4255@isr.umd.edu>
To: DAWG Mailing List <public-rdf-dawg@w3.org>

Working off:	

"""Definition: RDF Term

  An RDF Term is anything that can  occur in the  RDF data model."""

"RDF data model" is linked to section 3.1 (Graph Data Model) of the  
Concepts and Abstract Syntax document. That section is non-normative.  
The first line is also redundant, given the rest of the definition:

""" let RDF-U be the set of all  RDF URIs
  let RDF-L be the set of all  RDF Literals
  let RDF-B be the set of all  bNodes

  The set of RDF Terms, RDF-T, is RDF-U union RDF-L union RDF-B."""

So, I advise striking it or moving it to the explication text instead  
of the definition.

(It's possible to read section 3.1 so that "triples" can occur in the  
RDF data model, yet it's clear that triple are not, themselves" RDF  

"""Definition: Query Variable

  Let V be the set of all query variables. V and RDF-T are  disjoint."""

This doesn't look like a definition (i.e, there is no "such that"). It  
also not specified whether V is non-empty, and whether V is  
denumerable. Section 6.6 of C&AS makes these features clear for blank  

Perhaps this definition could read similarly, e.g.,

"A query variable is a member of the set V where V is infinite and  
disjoint from RDF-T. V is otherwise arbitrary."

The other possibility is to pick a non-arbitrary set with the desired  
features. E.g., V is the set of pair whose first element is the unicode  
string "?" and whose second element is an arbitrary unicode string. I  
believe such a V is disjoint from RDF-T, though you might make the type  
tag "<?>" to rule out bizarre uris of the future :)

(BTW, is there a strong motivation for the RDF- prefix? It seems otiose  
and is hard to read, IMHO)

It would be good to note in the comment on triple patterns with literal  
subjects that all Query Patterns will literal subjects will *fail* on  
any RDF document. I'm fine with them being legal in SPARQL, perhaps as  
a forward compatibility measure, but it's also nice to note their  
(current) futility.

"""Definition: Query Pattern

  A query has one main graph pattern. It is called the Query Pattern."""

There is no definition of Query.

There is no definition of Graph Pattern. (Basic pattern and Graph  
Pattern -- Grouping, yes. See my earlier message).

Can there be more than one main graph pattern? Are there non-main graph  
patterns? What's the difference?

Ok, taking a break now. Foward looking a bit I see there's some  
sloppiness with the term "pattern". For example:

"Definition: Constraints

  A pattern may be a constraint, which is a boolean-valued expression of  
variables and RDF Terms that restricts query solutions"

"A pattern"? A triple pattern? A graph pattern? Are constraints  part  
of Basic Patterns? (in which case, shouldn't they be part of the  
definition of basic pattern?) I'm afraid that order of exposition is  
getting in the way here.

More later, I imagine.

Received on Monday, 4 April 2005 20:16:49 UTC

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