From: Alan Ruttenberg <alanruttenberg@gmail.com>

Date: Wed, 9 Jul 2008 15:18:04 +0100

Message-Id: <B6C4FDAE-72C6-40CD-B856-86DD0B3D7ED2@gmail.com>

Cc: "'OWL Working Group WG'" <public-owl-wg@w3.org>

To: "Boris Motik" <boris.motik@comlab.ox.ac.uk>

Date: Wed, 9 Jul 2008 15:18:04 +0100

Message-Id: <B6C4FDAE-72C6-40CD-B856-86DD0B3D7ED2@gmail.com>

Cc: "'OWL Working Group WG'" <public-owl-wg@w3.org>

To: "Boris Motik" <boris.motik@comlab.ox.ac.uk>

On Jul 8, 2008, at 5:16 PM, Boris Motik wrote: > Hello, > > 1. Datatype Map > ---------------- I wonder if we should still use the term "datatype", as there will likely be confusion with the xsd sense of datatype. > A datatype map consists of the following things: > > - a set of datatypes > - each datatype provides a set of allowed facets > - a possibly infinite set of constants (likely to be renamed to > literals, but I'll stick to "constant" for the moment) > - each constant consists of a lexicalValue and a typeURI > - it is written as "lexicalValue"^^typeURI > > Each datatype DT is assigned a value space DT^D, which is just a > nonempty set. Is the implication that DT -> Value space DT^D, one to one? So we have type, DT, DT^D ? > Each constant c is assigned a value c^D, which is just an object > from the union of the value spaces of all datatypes. > > > Thus, a datatype can be thought as a class with a predefined > extension. I'm not sure explaining it this way is helpful - might confuse rather than illuminate. > Note that this definition does not assume any relationship between > the set of supported typeURIs (which determine the allowed > constants) and the set of datatypes (which determine the allowed > sets of values). I think we should consider calling "typeURI" "lexicalFormURI" to suggest the correct thinking, as people tend to equate "type" and "class". (as with rdf:type) Can we not simplify the above to: There are "Value spaces" and "lexicalFromURI"s. I'm not seeing how having "Datatypes" as an additional concept helps. > > 2. Allowed datatypes > --------------------- > > Comformant OWL 2 implementations would be required to support the > following base datatypes, each of whose value spaces would be > disjoint: > - owl:number - the value space is the set of all real numbers > - xsd:string - the value space is the set of all Unicode strings in > normal form C > - owl:internationalizedString - the value space set is the set of > pairs of the form (string,langTag) > - xsd:hexBinary - the value space is the set of all finite > sequences of octets I'm wondering whether we should simply say: OWL has the following (following your later mail). owl:Number owl:CharacterString owl:BitString owl:Integer We confuse the issue by using the xsd uris to name a different sort of thing (an OWL value space, not an XSD:type) > The following datatype would also be supported in OWL 2: > > - xsd:integer - the value space is the subset of the value space of > owl:number containing all integers See above. > Finally, we might support the following "shortcut" datatypes, whose > value spaces can be defined from the value spaces of the above > mentioned datatypes using facets > > - various xsd:integer derivatives, such as xsd:int and xsd:long > - various xsd:string derivatives, such as xsd:Name In order to keep the design clean, I'd suggest that we define these in the owl namespace. We can connect the xsd types to the owl version. However: The use of e.g. xsd:string in restrictions is the common idiom. I think we should document that some xsd datatypes, when used in a restriction, are understood to mean certain owl value spaces. > 3. Allowed constants > --------------------- > > Conformant OWL 2 implementations are required to support the > following constant types: > > - "nnn"^^xsd:int and all derivatives that fall within xsd:int - all > such constants are to be interpreted as elements of owl:number > - "aaEbb"^^xsd:float - all such constants save for NaN and +-inf > are to be interpreted as elements of owl:number Consider extending owl:number with these constants. We need some interpretation of them if they are to remain intact when part of an OWL file. These are effectively, "promotion" rules. > - "abc"^^xsd:string - interpreted as "abc" as you later suggest, ("abc", null) or ("abc", "") . The latter avoids the issue of what to do about the pattern facted on lang. > - "abc"@langTag - interpreted as a pair ("abc",langTag) > > > 4. Discussion > -------------- > > The set of constants is chosen such that implementations don't need > to support numbers with arbitrary precision, which might be quite > cumbersome. In fact, implementations are only required to support > 32 bit integers and single precision floating point numbers. On today's hardware, I would set this to be 64 bit integers or even 128 bit integers, and double precision float. Some machine's don't really have single float hardware, instead rounding from double float. > There are efficient ways to represent these on virtually all systems. > > The set of datatypes, however, allows one to refer to the sets of > all integers and real numbers. This allows one to specify the > ontology in a way that makes reasoning easy. > > Implementations are free to support other constants as well. Note > that these extensions do not necessarily mean that we need new > datatypes (i.e., new value spaces). For example, an implementation > might choose to support arbitrary precision numbers via constants > of the form "123.03"^^xsd:decimal. Note that the proposed list of > datatypes already contains the appropriate value space for such > constants (i.e., owl:number). I think xsd:decimal should be considered a lexical form of owl:Number. > The open issues are what to do with NaN and +-inf and with date- > time datatypes. In the first case, I suggest above that owl:Number be real+"NaN"+"- INF"+"+INF" I'd also suggest that "-0" and "+0" be considered lexical forms of the number 0. For the date-time datatypes, I wonder whether it would work to define: owl:Time (isomorphic to the reals) owl:TimeZoneTime (also isomorphic to the reals) There is one value space for all the lexical date-times have time zone specified, and another value space for all the lexical date- times. There would be no comparison possible between owl:Time and owl:TimeZoneTime. There would still be work necessary to determine whether the repeating interval types, like monday, are feasible to implement. -Alan > > Regards, > > Boris > > >Received on Wednesday, 9 July 2008 14:18:51 UTC

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