- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 21 Feb 2005 15:17:52 -0600
- To: Jeremy Carroll <jjc@hpl.hp.com>, pan@cs.man.ac.uk
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
- Message-Id: <p06200709be3fe5b011df@[10.100.0.9]>
Overall, great job of exposition, badly needed. ------------- Few typos/comments: section 2.2 You say that the use of simpleTypes#adultAge violates RFC2396, citing this: " The semantics of a fragment identifier is a property of the data resulting from a retrieval action, regardless of the type of URI used in the reference. Therefore, the format and interpretation of fragment identifiers is dependent on the media type [RFC2046] of the retrieval result. [...]" but I see no contradiction there. Indeed, one could use a retrieval action on http://example.org/simpleTypes, right? And it might be an RDF ontology, in which case the semantics might well be said to be a 'property of the data resulting from' the retrieval action. OK, Im splitting hairs, but we have to split hairs when dealing with out-of-date documents like RFC2396. Section 2.4 Daml//DAML You might also point out that the id= solution has the merit that according to Xpointer, "If no element information item is identified by a shorthand pointer's NCName, the pointer is in error." which means that the use of a URIref in this way whose root URI does not provide any (hopefully definitive) uses of the element is an error, which Im sure TBL will find congenial as a piece of Web discipline. . Section 2.5 "Both the XSCD and the id solutions have the problem that the proposed URI references designate a syntactic thing, rather than the datatype itself." Seems to me (maybe Im alone here, but ..) that this is just one example of a whole range of related issues about URI denotation, and that we should just grasp this nettle and say that URI's can IDENTIFY (RFC 2396) one thing (typically syntactic, seen from a SW perspective) and also, and simultaneously, DENOTE something else; and that this is quite OK as long as the thing they identify (is closely related to something that) denotes the thing they denote. And this is not URI punning (a Tag Bad Thing) but rather a systematic way of relating identification with denotation. It does not rule out the simple URN case where identify=denote, but it allows a 2-step version URIref--indicates-->piece of syntax--denotes-->thingie which can also be contracted to be URN-like: URIref--denotes-->thingie where convenient (as for example in RDF). Then this takes care of the second problem with the wording of 2396, which you cite: "A fragment identifier is only meaningful when a URI reference is intended for retrieval and the result of that retrieval is a document for which the identified fragment is consistently defined." 3.1 Or in other words, when are two literals, which are written down differently, refer to the same value // referring to the same value OR: //when do two literals --- 3.2 the RDF and OWL Semantics are Semantics//semantics -- Similar OWL DL entailments could be constructed, illustrating the same issues. why didn't you give DL examples, then? (Question springs to the reader's mind at this point.) -- 3.2.1 Example uses "15.0"^^xsd:decimal but then switches to "15"^^xsd:decimal Example 3J says 'this is only a rounding error' but you might observe that since it is possible to express restrictions on such values in OWL, ignoring rounding errors can give rise to clear inconsistencies. Your phrasing makes it sound like an unimportant kind of issue. 3.3 You might remark that the relation ~ is conventionally written as '=' and called equality. The formal definition you give is slightly broken, since you say that ~ is a relation, but you equate it to a class. Also, IL and Ed are not strictly speaking invertible. ( I see what you mean, but you are using mathematical abuses of notation that might confuse some readers.) This might be better: ~ = {<x,y> : IL(x)=IL(y) } and the equivalence classes are defined slightly circularly in this way: X= { x: IL(x)=IL(y) for any y in X} Or, less circularly, as X = {x: IL(x)=z } for some value z, where this is the equivalence class of expressions denoting the given literal value z. (But not X= {x: exists z. IL(x)=z} :-) --- section 5 measurement.... The actual value is unknowable, but more precise measurement methods can reduce the range of uncertainty up to a point. "up to a point" is perhaps an unfortunate way of phrasing it (unless its a small joke.) seperate //separate This value denotes a value range which includes the actual value." ; Well not exactly. Might be better to say that it 'indicates' a value range. But in fact in real engineering apps the error range is usually specified somewhere, perhaps contextually, so what denotes the value range is not the value itself but the value plus the error range. The basic point is that measurements are typically given as a number and one or more error ranges, and clearly xsd:decimal refers to the former but not the latter. This needs noting because of the common engineers convention of indicating the error range by the number of decimal places given, so 2.00 is 2 plus or minus 0.009. --- "This is not a bad approach any since there are" //.. approach in any case, since... BTW, there is an issue here that you don't address. Typical error ranges are stated as bounds ("+ or - 0.001 cm"). OK, but what datatype should be used to state the bounds themselves? Would it make sense to write something like "32.65++0.001"^^xsd:boundederrorfloat ? That would be extremely convenient for engineering applications, but it requires treating the 0.001 differently (exactly) from the literal value itself (approximate). Could this be defined as an xsd derived datatype? --- underlaying//underlying (underlay is what you put under a carpet) Appendix A Might be interesting to relate the RDF/OWL definitions to the XML definition given at the start. XML doesnt mention value spaces at all, and its use of 'facets' strongly suggests that the XML view simply allows questions of identity to be highly contextual, in contrast to the model-theoretic approach we used. Might be worth expanding on this difference, which is responsible IMO for many of the complexities and ambiguities you discuss. --- As far as OWL Full is concern, the disjointness restriction about object and datatype domains is not required. // In OWL Full, the disjointness restriction between... -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32502 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 21 February 2005 21:18:39 UTC