From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 10/11/01
The more I look at Pat's new proposal, the more I like it. However, there is not just a notational difference between Pat's proposal and mine, there are real differences. Think of it the following way: I tried to get a model theory that was able to determine the map from literals (05) to literal values (the integer 5 or the string "05") from semantic information, such as range restrictions on properties. Pat's proposal determines this map via strictly syntactic means, i.e., from the RDF graph. Both proposals restrict the denotation of literals using semantic means, so that a range restriction on age to xsd:integer would require that all literal values that are objects of the age relationship belong to the value space of xsd:integer (namely integers). My proposal would have problems when local syntactic information, such as <age xsd:integer>05</age>, clashed with semantic information, such as the range of age is the XML Schema Datatype union of xsd:string and xsd:integer, because it would have no mechanism for preferring the local information over the other information. (There might be a way of fixing this but it would not be pretty.) I think that Pat's proposal has some places where it might be considered to diverge from XML Schema datatypes. For example, if you don't have any syntactic type information, say as in <John age 05> but you do have semantic type information, say as in <age range XS??:(union integer string)> then you could not deduce that John's age is the integer 5, only, perhaps, that it is either the integer 5 or the string "05". (Note that I'm extending Pat's solution a bit here, at least I think that I am.) In a strange sense, Pat's proposal is closer to the solution in DAML+OIL than mine is. All that said, I think that I'm willing to go with Pat's proposal. At least I'm willing to try to get it nailed down and see what its consequences are. Peter F. Patel-Schneider Bell Labs Research
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