- From: Frank Manola <fmanola@mitre.org>
- Date: Fri, 14 Feb 2003 12:02:50 -0500
- To: w3c-rdfcore-wg@w3.org
Following up on item 9 in today's agenda, here are some potential problem areas in Concepts and Vocabulary (I don't claim these are exhaustive): Concepts Section 3.1 begins: "The underlying structure of any expression in RDF can be viewed as a directed labelled graph, which consists of nodes and labelled directed arcs that link pairs of nodes (these notions are defined more formally in section 6). The RDF graph is a set of *triples*: [image of the RDF triple comprising (subject, predicate, object)] Each property arc represents a *statement* of a relationship between the things denoted by the nodes that it links, having three parts: 1. a property that describes some relationship (also called a predicate), 2. a value that is the subject of the *statement*, and 3. a value that is the object of the *statement*. The direction of the arc is significant: it always points toward the object of a *statement*. The meaning of an RDF graph is the conjunction (i.e. logical AND) of all the *statements* that it contains." I've highlighted *triple* and *statement* in the above. The text seems mostly to be talking about the subject/predicate/object of *statements*, except for the introduction, which seems to suggest it's talking about *triples*. A question is whether we're going to use subject, predicate, and object for talking both about components of triples, and components of statements and, if so, how we keep them straight. Note that the abstract syntax uses these terms to refer to parts of *triples*. Also, in bullets 2 and 3, tht term "value" is a bit ambiguous: it could be read either as referring to a URIref, or to the thing denoted by that URIref. Given the wording in the preceding phrase, changing "a value" to "the thing" would clarify that it was talking about the thing denoted, rather than the URIref (if that's what it is talking about). Concepts Section 3.4, the third sentence, says: "A literal may be the object of an RDF *statement*, but not the subject or the arc" This seems to mix several things. A literal sounds like the lexical thing, which would be a reasonable object of a triple, but less-clear for a statement (presumably it's the value denoted by the literal that would be the object of a statement). "Arc" seems to be mixing in the drawing terminology from Section 3.1, and it's not clear it belongs here. Concepts Section 3.5 starts: "Some simple facts indicate a relationship between two objects. Such a fact may be represented as an RDF triple in which the predicate names the relationship, and the subject and object denote the two objects." In this section, the term "fact" is used as the thing represented as an RDF triple. In Section 3.1 the thing represented as a triple seemed to be a "statement". There may or may not be a problem using "fact" in this kind of text, but its relationship to "statement" needs to be made clear. Also, "object" is used in two different ways, as the things denoted by subjects and objects, and as the third component of a triple. Vocabulary Section 5.3.1: This section starts with some nice text that is clearly about subjects, predicates, and objects of *statements*. Section 5.3.2 (rdf:subject) then says: "A *triple* of the form: S rdf:subject R states that S is an instance of rdf:Statement and that the subject of S is R" This may or may not be problematic. The question is whether the reader will interpret S and R as the URIrefs involved in the corresponding triple, or as the resources denoted by S and R. Similar comments apply to sections 5.3.3 and 5.3.4. --Frank -- Frank Manola The MITRE Corporation 202 Burlington Road, MS A345 Bedford, MA 01730-1420 mailto:fmanola@mitre.org voice: 781-271-8147 FAX: 781-271-875
Received on Friday, 14 February 2003 11:43:40 UTC