- From: Jeff Pan <pan@cs.man.ac.uk>
- Date: Wed, 26 Jan 2005 17:14:02 -0000
- To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
- Cc: <www-archive@w3.org>
Hi Jeremy, Sorry for the delay. > Summary: > - in-line thoughts about Evan's general comments > - action plan??? > > > I've been a bit remiss in not driving forward with this. We're meant to > have a new version for Thursday. > > I think we've basically got the detailed comments dealt with, except for > actually editing. > > I think we don't have to resolve the question between us of how much > does OWL DL cover user defined datatypes or not (although we should try > and have a verbal discussion about this, maybe in Boston - I think it > would be interesting). I think your DL material is relevant whether or > not OWL already presupposes it (it certainly doesn't adequately document > it). OK. > Going through Evan's comment in-line: > > ewallace@cme.nist.gov wrote: >> My review of "XML Datatypes in RDF and OWL" [1] >> >> Overall, this is a good document. It discusses a number >> of issues related to the use of datatypes in RDF and OWL that were left >> unresolved by the Recommendations. It is comprehensive in addressing >> the issues discussed: covering alternative approaches and providing >> appropriate references and/or quotes as necessary. In fact, because >> of this comprehensiveness and the importance of the references, >> reviewing this document was more of a project than I had originally >> envisioned (although reading these references proved enlightening).. >> >> I have no major issues with this document, although I do have some >> lesser concerns and comments. These fall into two categories: general >> and detailed. The detailed concerns were already presented in an >> email sent to the list yesterday [details]. The general concerns >> follow below. >> >> >> * The document covers a number of loosely related subjects. It is >> like a bag of datatype issues and other related material. Different >> parts will be of interest to different audiences. I mentioned this >> before, but my main concern now is that someone reading linearly >> through the document will encounter the interpretation descriptions >> in 1.2, 1.3, and 1.4 and stop reading. >> I think such material would >> be better placed as an appendix. > > Really for you to either agree with or argue against. > > I tend to agree with Evan and would suggest following changes: > > Merge current > > 0. Intro and 1.1 XML Schema > > with > > 1. Intro > > Current text without namespaces stuff > > 1.1 Structure of this document > > Give an indication of the intended reader and role of each section > > In particular highlight the role of DL stuff as providing theoretical > background for the meaning of user-defined datatypes in OWL DL, and role > of appendix as supplementing material in RDF and OWL Semantics to cover > this document. We could provide an overview of Appendix B at the beginning of Section 2 (before Sec 2.1), making it clear that in the rest of Section 2 we discuss only the URI problem. I can further comment on these parts once I see your draft tomorrow morning. > 1.2 Namespace declarations > > 1.3 XML Schema stuff > New appendix > > A. (Title?) > > A.1 old 1.2 > A.2 old 1.3 > A.3 old 1.4 We could structure the above three sections as follows. A. Summaries of RDF and OWL Datatyping A.1 old 1.2 A.2 old 1.3 B. Integrating Description Logics with User-Defined Datatypes old 1.4 Note that example IDs should change accordingly. >> It was also not clear to me the >> purpose and role of such material in this document. By role, I mean >> are the interpretation descriptions in 1.2 and 1.3 quotes from the >> RDF and OWL semantics documents respectively or a different form for >> the same content? >> > > We should add URLs to the respective documents and indicate clearly any > differences if any. >> * An important reference for datatypes in computing environments is >> the ISO standard on Language-independent datatypes - ISO/IEC >> 11404:1996. It provides an excellent framework for describing >> datatypes and appears to have been a strong influence on the XML >> Schema base types document [2] (which includes a reference to >> 11404). The XSCH note could benefit referencing the ISO work >> directly and using some of its terminology, although I don't think >> that this is necessary for this iteration of the note. >> > > Suggest we add the reference and a single sentence in the XML Schema > introductory section. OK. >> * My primary interest in these datatype issues is with the treatment >> of numeric types being consistent with their use in engineering >> applications (or at least usable by those applications). Loss in >> precision or unexpected changes in values due to automatic type >> conversion could be problematic in an engineering environment. >> >> Engineering view of some numeric types: >> >> To explain the engineering point of view on this, let me mention >> three important numeric types for that domain: count, measurement, >> and constant. >> >> A count is an integer representing essentially the >> cardinal number for a set of things classified by some set of tests. >> An example would be the count of packages of candy available for >> shipment. A count is an exact number. Tests may include >> measurements, but a count is not an approximation of a sum of >> these measurements nor is it a sum of the approximation of these >> measurements. >> >> A measurement is an inexact numeric value (usually represented as a >> real) produced by some measurement method. This value denotes a >> value range which includes the actual value. The actual value is >> unknowable, but more precise measurement methods can reduce the >> range of uncertainty up to a point. The precision or uncertainty is >> usually included with the measurement value. Either implicitly >> using significant figures or explicitly using a seperate property >> value such as error range. >> >> A constant is an exact value used in computation. It may or may not >> be possible to express exactly as a numeric. An inch is exactly >> 2.54 centimeters, but Pi is not 3.14159. >> >> This suggests some potential needs and concerns for a type system >> underlaying this. 1. Because the value spaces for these types >> are different, measurements are disjoint from counts and constants. >> 2. Some means of capturing precision or error/uncertainty is needed >> for measurement values. 3. Some means is needed for denoting >> constants that cannot be expressed precisely in numeric form. >> >> Some answers about how 1 and 2 can/must be handled with XML Schema >> types are revealed in the XML Schema Datatypes document. In [2] the >> description for Decimal explicitly states that, "Precision is not >> reflected in this value space, the number 2.0 is not distinct from >> the number 2.00." Thus precision cannot be encoded in decimal >> values or other types derived from or constructed with >> Decimal. Meaning: that objects must used to state precision or error >> properties for measurements (this is not a bad approach any since >> there are often other properties or metadata associated with a >> measurement as mentioned previously by Bernard [3]). Measurements >> on the SW are thus not datatypes and the disjoint type issue becomes >> mute. >> > > > At telecon I agreed to draft a new section based on this point, I would > put it before the appendix. It could be a second appendix, although it > feels less heavy than typical appendix material. I am not too sure if I have enough time to provide much comments on this tomorrow, although I second the idea of having such a section. >> For issue 3, there remains no answer. As far as I know there is no >> way to denote a rational value without using a numeric literal, but >> many important values cannot be expressed precisely as numeric >> literals. >> >> Information on these issues may belong in this datatype note or not, >> I am not sure. I do think that the SWBPD wg should present these >> issues in some one of its notes, though. >> >> -Evan >> >> [1] http://www.w3.org/2001/sw/BestPractices/XSCH/xsch-sw/ >> [2] http://www.w3.org/TR/xmlxschema-2/ >> [3] http://lists.w3.org/Archives/Public/public-swbp-wg/2004Dec/0119.html >> [details] http://lists.w3.org/Archives/Public/public-swbp-wg/2005Jan/0040 >> > > > > I'm happy to have a stab at making all these changes except for changes > inside your text (other than those precisely described in your e-mail > response to Evan). The most notable thing I would be missing is links > into the semantics docs for how the current sections 1.2, 1.3, 1.4 > relate to them. I would leave clear markers where I need your help and > hopefully have this ready in time .... Here are the URLs: RDF: http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#DTYPEINTERP OWL: http://www.w3.org/TR/2004/REC-owl-semantics-20040210/direct.html#3.1 Unary datatype group: [Pan2004] Jeff
Received on Wednesday, 26 January 2005 18:38:18 UTC