Comment on Last Call Working Draft of RDF Syntax document concerning blank node identifiers (original) (raw)

The handling of blank nodes is still problematic in the LCC version of the RDF Syntax document.

The intent is clear. Each nodeElement that does not otherwise get a subject is given a blank node identifier as a subject. The string-value of this blank node identifer is to be different from the string-value of every other blank node identifier resulting from the parsing of the RDF/XML document.

However, the document does not follow this intent.

First, in section 5.2, the document only says that ``generated blank node identifiers must not clash with any blank node identifiers from rdf:nodeID attribute values.'' This allows

<rdf:RDF xmlns:rdf="..." xmlns:ex="...">

rdf:Description ex:foo <rdf:Description />

to generate the following triple

_:x ex:foo _:x .

Second, a blank node identifier in the linear representation of an RDF Graph is generated from the string-value of the subject of the event. For events that come from nodeElements that have an rdf:nodeID attribute, this value is determined in 7.2.11 as follows If there is an atribute a with a.URI=rdf:nodeID, then e.subject := bnodeid(identifier:=a.string-value)'' From 6.1.7 the string value of this subject is the concatenation of "_:" and the value its identifier accessor, which is determined during the construction of the event by giving a value for the identifier accessor''.

This means that

<rdf:RDF xmlns:rdf="..." xmlns:ex="...">

<rdf:Description rdf:nodeID="HI"> ex:foo <rdf:Description rdf:nodeID="BYE" />

MUST generate the following triple

_:HI ex:foo _:BYE .

Therefore the wording in 5.2 ``One method would be to add a constant prefix to all the rdf:nodeID attribute values'' is not a potential solution to the blank node identifier clashing problem, as it clashes with the required method of determining the string-value of such blank nodes.

Received on Tuesday, 28 January 2003 09:17:53 UTC