- From: Frank Manola <fmanola@acm.org>
- Date: Tue, 20 Jan 2004 09:37:28 -0500
- To: Chris Bizer <chris@bizer.de>
- Cc: www-rdf-comments@w3.org
Hi Chris-- Thanks for the comments. I don't disagree with the idea of encouraging people to think about using URIrefs in place of literals. However, I think the Primer goes as far as it needs to in this regard. In the first place, I think most RDF novices need to be *explicitly introduced* to the idea of using URIs for what are conventionally represented by literals (like "Dr."), rather than this use suddenly appearing (let alone appearing "exclusively" throughout the Primer). Hence, the Primer mainly (except for the "fast forward" in the intro) starts out using URIs (actually URLs) to identify something that most Web users would already expect them to be used for: a Web page; and using literals for other things. The Primer then explicitly points out the extended use of URIs to identify other things, like people and predicates, and then discusses the potential value of using URIs instead of literals to identify things. In the second place, using a mixture of literals and URIrefs to describe things is the real world, and will be for some time, if not forever (URIrefs are just names for things; people continue to use combinations of names and descriptions employing literals to describe things). Requiring the exclusive use of URIrefs for literals in the Primer would, for example, preclude presenting any of the example applications in Section 6 (none of which use URIrefs exclusively for these sorts of things). Simply using URIrefs (e.g., for a conventional title like "Dr.") doesn't magically improve interoperability; it has to be a *common* URIref; one whose meaning is generally shared. For example, whose URIref for "Dr." are you suggesting should be the one that appears in the Primer? In this case, until better community consensus arises (and maybe even after), I'd bet that a literal like "Dr." will serve fairly well to indicate this title, given its fairly-universal use right now (certainly better than a non-standard URIref). The same holds for city and state names, zip codes, and so on (some of which have values that are explicitly intended as unique identifiers). Everyone making up their own URIrefs for such things as titles won't help very much. I also think some of the best practice in this area needs to evolve, rather than the Primer talking as if it already existed (let alone appearing to dictate it). Take a Zip code, for example. Is it best modeled as: * a URI like usps:01730 (with "usps" representing a prefix officially defined by the US Postal Service) as the value of a predicate like ex:postalCode? * a typed literal like "01730"^^usps:zipcode as the value of the same predicate (in this case, the USPS is defining a datatype for Zipcodes)? * the same typed literal, but as the value of a USPS-defined predicate usps:postalCode (or a corresponding internationally-defined datatype and predicate)? * the original plain literal, but as the value of the USPS-defined predicate? Note that the title "Dr." in the first Primer example is the value of a predicate from a specified vocabulary (the SWAP contact vocabulary), so intended meaning of the literal value is not totally undefined, and, as the examples above suggest, I think the identification of the predicate has a place in this discussion. There's a proposal for a Semantic Web "best practices" working group floating around (see message http://lists.w3.org/Archives/Public/www-rdf-interest/2003Nov/0055.html) and I expect that group, should it actually start work, will contribute to the understanding of some of these issues. At this point, I think the Primer is doing its job if it makes novices aware that there's an issue here, without trying to suggest that all the decisions about best practice have already been made. --Frank Chris Bizer wrote: > Hi, > > a small but maybe didactically important comment on the usage of literals > in figure 1 and 5 of rdf- primer (also cited in rdf-concepts). > > It is stated that Eric has the personal title "Dr." using a literal. > Following common RDF modelling principles, an URIref should be used to > identify the concept of "Dr." as an academic title. > > I think I might be confusing for a RDF novice to be taught in section 2.1 > and 2.2 to use URIs to identify the creator of a webpage and then to have > examples in the same document, that do exactly the opposite. > > The same problem appears to the example in figure 5 where the properties of > an address (City, State, ...) are described using literals, which is deadly > for any graph merging. > > I think it is important to use URIrefs instead of literals in the examples. > These examples will be copied into hundreds of introductions to RDF and will > otherwise confuse beginners. > > You could also think about changing the sentence "In fact, a URI can be > created to refer to anything that needs to be referred to in a statement, > including ..." in section 2.1. into "In fact, a URI *should be used* to > refer to anything that needs to be referred to in a statement, including > ..." in order to make good modelling practices clearer. > > > > Chris Bizer > > > >
Received on Tuesday, 20 January 2004 09:37:19 UTC