- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Thu, 08 Jan 2015 18:40:43 -0800
- To: Holger Knublauch <holger@topquadrant.com>, "public-data-shapes-wg@w3.org" <public-data-shapes-wg@w3.org>
On 01/08/2015 05:13 PM, Holger Knublauch wrote: > On 1/6/2015 1:06, Peter F. Patel-Schneider wrote: >> There still appears to be some disagreement. > > As Peter made it clear that he feels very strongly about this issue, I would > like to follow up towards a resolution even though I think we could also delay > the specific question until it comes back (in the context of :valueType). > > The remaining question to me is that if we mint our own property :valueType > which of the following options is best (for the community): > > a) We make a clear statement in the documentation of :valueType that the > following meaning is assumed (we can even state that this slightly deviates > from its use in rdfs:range): > > - :valueType is empty -> no constraint > - :valueType = rdfs:Resource -> IRI or blank node > > From my experience if I look outside of the W3C WG microcosm, I believe the > above would be best aligned with the current practice. This is absolutely counter to the requirement that the working group must use rdfs:Resource in a way that abides by its meaning as defined in the RDF specification. > b) We introduce another property :nodeType with values (:Literal, > :BlankNodeOrIRI, :BlankNode, :IRI) and assume that :valueType = rdfs:Resource > means unconstrained and people need to combine it with :nodeType), i.e.: > > - :valueType = rdfs:Resource (or empty) && :nodeType = :BlankNodeOrIRI -> IRI > or blank node This mints new terminology and thus does not run counter to the requirement that the working group must use rdfs:Resource in a way that abides by its meaning as defined in the RDF specification. > Questions: > > 1) Peter, would option b) work for you, if a) doesn't? I have no problem with option b) not abiding by the requirement that the working group respect pre-existing terminology. > 2) Assuming I also state that I feel strongly about this, what does the WG do? > Does this mean that we have a deadlock and no further progress can be made? I > believe both view points are valid, so instead of simply putting a veto on the > table, I think a proper process would be to at least allow others to speak up > and have a vote, then re-evaluate whether the veto is still appropriate? > > BTW I can live with option b) but I am afraid we are exactly repeating the > mistakes that other WGs have made in the past, by putting theory before > practice. I predict this will be one of the issues that most users will find > unintuitive and that we will have to explain to users over and over again > (just like we now have to explain the weird semantics of rdfs:domain over and > over again). > > Thanks, > Holger > > >> >> I do not believe that the working group can use rdfs:Resource in any way >> other than as the class of all resources. The only exception would be in >> situations where all classes have special behaviour, such as using classes >> to control the operation of constraints. This would have to be done in a >> uniform manner, and the wording would have to be carefully chosen to ensure >> that no confusion would arise. >> >> peter >> >> >> On 01/05/2015 05:37 AM, Johnston, Patrick - Hoboken wrote: >>> I agree. Can we put this one to bed and move on? >>> >>> We can't fix previous specs here, but we can ensure that the documents we >>> produce are intellectually accessible and not needlessly esoteric. We're >>> not trying to make Rdf popular, we're trying to help it grow up so that it >>> can play compatibly with the web and data description languages it >>> straddles. Popularity will come only if it is useful to the wider community >>> and we can talk about it in terms of what it does rather than what it is. >>> >>> Patrick >>> >>>> On Jan 4, 2015, at 7:13 PM, Holger Knublauch <holger@topquadrant.com> wrote: >>>> >>>> I agree we should use the term "resource" consistently with other RDF >>>> specs inside of our own specs. The target audience of those formal specs >>>> is comparably small and average users will learn the shapes language >>>> from other tutorials and example snippets anyway. The best approach >>>> might be to avoid the term "resource" and use "IRI or blank node" in >>>> suitable places. >>>> >>>> With the meaning of rdfs:Resource in the context of property ranges, I >>>> believe we do have flexibility as long as we do not overload and reuse >>>> the properties rdfs:range or owl:allValuesFrom. If we coin another >>>> property (such as :valueType) then I believe we do have the freedom to >>>> specify that *in the context of this property*, using rdfs:Resource >>>> means "IRI or blank node", because this is the de-facto interpretation >>>> that the majority of users will more easily understand. Just leave the >>>> :valueType empty to mean "any node". >>>> >>>> I had sent the link to the Google trend for RDF in a previous email. >>>> This is not the only evidence that RDF has not succeeded in attracting a >>>> large user base. I believe if we want to relaunch interest in RDF then >>>> we need to focus on its good bits and work around the things that did >>>> not work well. Many design decisions in RDF Schema and OWL in particular >>>> were made with other use cases in mind. Some naming decisions were >>>> unfortunate including rdfs:Resource but also owl:ObjectProperty (the >>>> term "object" is used in triples). For these reasons I am against a >>>> general assertion that we must slavishly follow in the footsteps of the >>>> previous RDFS/OWL specifications. Instead I suggest we try to keep our >>>> documents as self-contained as possible, so that potential users and >>>> implementers can understand the relevant background without reverting to >>>> other complex and often contradicting specs. >>>> >>>> Holger >>>> >>>> >>>>> On 1/4/2015 13:50, Peter F. Patel-Schneider wrote: >>>>> There may be multiple communities in this discussion, but the working >>>>> group exists in the W3C RDF space. I thus feel very strongly that the >>>>> working group must not produce documents that use core W3C and RDF >>>>> terminology in ways counter to their meaning within W3C and RDF. >>>>> >>>>> peter >>>>> >>>>> PS: By the way, I don't particularly like this particular terminology. >>>>> >>>>> >>>>>> On 01/03/2015 11:35 AM, Karen Coyle wrote: >>>>>> In the email below I readily conceded that rdfs:Resource belongs to >>>>>> the RDF >>>>>> context and is specific to the definition given in that context. But >>>>>> "resource" is a word that already belongs to a larger populartion >>>>>> than RDF >>>>>> standards. When we use the term we must be clear which context we >>>>>> mean. We >>>>>> cannot, however, limit our use to the definition given in RDF >>>>>> documentation >>>>>> unless we are only specifically referring to that meaning, and only >>>>>> speaking >>>>>> to a very narrow cohort. >>>>>> >>>>>> As I'm sure you're aware, prescriptive linguistics fail outside of >>>>>> highly >>>>>> specific environments. Not wanting to be part of a limited society, I >>>>>> prefer >>>>>> clarity of context. >>>>>> >>>>>> Relating back to something that came up between Peter and Arthur, >>>>>> there are >>>>>> indeed multiple communities in this discussion. There is also a broad >>>>>> audience >>>>>> range. As the Dublin Core community learned during its development, >>>>>> adoption >>>>>> of a standard is greatly aided by broadening, not narrowing, the >>>>>> potential set >>>>>> of users. I hope we can do the same here. >>>>>> >>>>>> kc >>>>>> >>>>>>> On 1/2/15 10:36 AM, Peter F. Patel-Schneider wrote: >>>>>>> Resource is a term defined in several W3C documents. In particular, >>>>>>> RDF >>>>>>> 1.1 Concepts and Abstract Syntax has a section on Resources and >>>>>>> Statements, >>>>>>> http://www.w3.org/TR/rdf11-concepts/#resources-and-statements, where >>>>>>> resources are stated to be the things that are denoted by IRIs and >>>>>>> literals (and blank nodes, too, but this comes later). Here is one of >>>>>>> the places where "resource" is defined as the universal category. >>>>>>> >>>>>>> This working group is an RDF working group and is obliged to use words >>>>>>> like resource in the way they are defined in the RDF specifications, >>>>>>> unless there is no chance that the use of such words could be >>>>>>> considered >>>>>>> to refer to their RDF meanings. >>>>>>> >>>>>>> >>>>>>> rdfs:Resource an IRI that is given a fixed meaning in a section of RDF >>>>>>> Schema 1.1 >>>>>>> http://www.w3.org/TR/2014/REC-rdf-schema-20140225/#ch_resource. >>>>>>> rdfs:Resource there defined as the class of everything. All resources >>>>>>> are instances of this class. The definition is made formal in a >>>>>>> section >>>>>>> of RDF 1.1 Semantics >>>>>>> http://www.w3.org/TR/2014/REC-rdf11-mt-20140225/#rdfs-interpretations. >>>>>>> >>>>>>> This working group is similarly obliged to use IRIs like rdfs:Resource >>>>>>> in the way they are defined in the RDF specifications. >>>>>>> >>>>>>> >>>>>>> >>>>>>> It is certainly the case that the RDF meaning of resource is different >>>>>>> from the RDF meaning of rdfs:Resource. However, both of these are >>>>>>> vital >>>>>>> parts of RDF, and have meanings in RDF that this working group is >>>>>>> obliged to defer to. >>>>>>> >>>>>>> >>>>>>> peter >>>>>>> >>>>>>> >>>>>>> >>>>>>>> On 12/23/2014 07:47 AM, Karen Coyle wrote: >>>>>>>> >>>>>>>> >>>>>>>>> On 12/22/14 7:25 PM, Peter F. Patel-Schneider wrote: >>>>>>>>> Agreed. I did not provide any examples concerning problems that such >>>>>>>>> misconceptions have caused. >>>>>>>>> >>>>>>>>> How about the recent discussion concerning "resource" in resource >>>>>>>>> shapes >>>>>>>>> as a proximate example? How about the difference between >>>>>>>>> "resource" in >>>>>>>>> RDF and "resource" in several RDF APIs? >>>>>>>> >>>>>>>> The difference we've been discussing, as I've understood it, is >>>>>>>> between >>>>>>>> rdfs:Resource and "resource". The former is formally defined and one >>>>>>>> should >>>>>>>> abide by that definition when using rdfs:Resource. The latter is a >>>>>>>> general >>>>>>>> term in English with a less precise meaning, and, AFAIK, anyone can >>>>>>>> give it a >>>>>>>> meaning in their own API. There is no reason to assume that it means >>>>>>>> the same >>>>>>>> as rdfs:Resource. Nor that the word "thing" means the same as >>>>>>>> owl:Thing. I >>>>>>>> admit that I use the terms "resource" and "thing" frequently without >>>>>>>> intending >>>>>>>> their RDF meanings; in particular, "resource" is commonly used in >>>>>>>> libraries >>>>>>>> and archives to mean "the created resource which we are describing." >>>>>>>> >>>>>>>> It might be a good idea to avoid using "resource" in an RDF-related >>>>>>>> context in >>>>>>>> a way that might be confused with rdfs:Resource. It depends, as Irene >>>>>>>> says, on >>>>>>>> whether users in that context with be confused. I could definitely >>>>>>>> imagine >>>>>>>> using "resource" in a user interface for metadata creation, or a user >>>>>>>> display. >>>>>>>> My users will be totally unaware of the existence of rdfs:Resource. >>>>>>>> "Resource >>>>>>>> shapes" works for me. I'm not comfortable with a re-defining of >>>>>>>> rdfs:Resource >>>>>>>> to mean "an IRI or a blank node" because it already has a precise >>>>>>>> definition >>>>>>>> that is different from that. I don't know what the use is in the APIs, >>>>>>>> but >>>>>>>> it's possible that the use of "resource" does not cause confusion. >>>>>>>> >>>>>>>> kc >>>>>>>> >>>>>>>>> >>>>>>>>> peter >>>>>>>>> >>>>>>>>> >>>>>>>>>> On 12/22/2014 07:18 PM, Irene Polikoff wrote: >>>>>>>>>> Peter, >>>>>>>>>> >>>>>>>>>> This is a an abstract theoretical statement not supported by any >>>>>>>>>> specific real practical examples. >>>>>>>>>> >>>>>>>>>> We have had many years of practice. By "we" I mean software >>>>>>>>>> professionals. In practice, multiple data models have been in use >>>>>>>>>> for >>>>>>>>>> a long periods of time - for example XML and relational databases to >>>>>>>>>> name the most popular ones. These models do not make a point to talk >>>>>>>>>> about the distinction between the data structures and things in the >>>>>>>>>> world the data represents. Their lack of attention to this >>>>>>>>>> distinction >>>>>>>>>> has not prevented them from being hugely successful and used in >>>>>>>>>> pretty >>>>>>>>>> much every piece of software today. >>>>>>>>>> >>>>>>>>>> Further, I am not aware of any software professional who have ever >>>>>>>>>> confused the data structures with the things they represent. >>>>>>>>>> Every one >>>>>>>>>> understands clearly and unambiguously that the information space is >>>>>>>>>> just that - information. A graph with data about Dick Chaney is just >>>>>>>>>> data, not the person. To my knowledge, no one have ever had a >>>>>>>>>> misconception about it. Based on the experience to date, the >>>>>>>>>> probability of anyone having such misconception in the future is >>>>>>>>>> extremely low. >>>>>>>>>> >>>>>>>>>> I am certain there are challenges in creating a useful standard >>>>>>>>>> specification, but this one seems to be the least of the issues. >>>>>>>>>> >>>>>>>>>> If you have examples of the real (not a casual colloquial speech) >>>>>>>>>> confusion between RDF nodes as data and resources in the world as >>>>>>>>>> things, I'd like to hear about them and learn about the problems >>>>>>>>>> they >>>>>>>>>> have caused. >>>>>>>>>> >>>>>>>>>> Irene >>>>>>>>>> >>>>>>>>>> >>>>>>>>>>> On Dec 22, 2014, at 8:31 PM, "Peter F. Patel-Schneider" >>>>>>>>>>> <pfpschneider@gmail.com> wrote: >>>>>>>>>>> >>>>>>>>>>> The danger is that one talks about a node when one means to talk >>>>>>>>>>> about a resource, or vice versa. This can be benign, if the >>>>>>>>>>> misconception either is not important or can be easily fixed, or >>>>>>>>>>> serious, if the misconception matters and is not easy to fix. >>>>>>>>>>> >>>>>>>>>>> When one is writing specifications, the only safe assumption is >>>>>>>>>>> that >>>>>>>>>>> misconceptions are matter and are not easy to fix, because one does >>>>>>>>>>> not know the contexts in which one's terminology will be used. >>>>>>>>>>> >>>>>>>>>>> peter >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>>> On 12/22/2014 04:59 PM, Irene Polikoff wrote: >>>>>>>>>>>> So, let's say there is a theory and meta theory and even several >>>>>>>>>>>> layers of it. There used to be a joke slogan in the OO community, >>>>>>>>>>>> btw, "Anything you can do, I can do meta". And let's say, these >>>>>>>>>>>> get >>>>>>>>>>>> conflated. >>>>>>>>>>>> >>>>>>>>>>>> Who and what will such conflation impact negatively? What systems >>>>>>>>>>>> and applications get broken? How will it change what people who >>>>>>>>>>>> are >>>>>>>>>>>> using the standards to build solutions are doing and how they are >>>>>>>>>>>> putting the technologies to work? >>>>>>>>>>>> >>>>>>>>>>>> In other words why is this important and what parts are important? >>>>>>>>>>>> >>>>>>>>>>>> Irene >>>>>>>>>>>> >>>>>>>>>>>> Sent from my iPhone >>>>>>>>>>>> >>>>>>>>>>>>> On Dec 22, 2014, at 12:28 PM, "Peter F. Patel-Schneider" >>>>>>>>>>>>> <pfpschneider@gmail.com> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> Being the same is a concept that needs clarification here. >>>>>>>>>>>>> >>>>>>>>>>>>> Yes, "2"^^xs:integer is a literal and ex:two is a URI. These >>>>>>>>>>>>> cannot be the same in RDF because URIs, blank nodes, literals are >>>>>>>>>>>>> disjoint. However, ex:two can be required to denote an integer, >>>>>>>>>>>>> which is a literal value. >>>>>>>>>>>>> >>>>>>>>>>>>> Yes, there is no atomic name in the metatheory of RDF that stands >>>>>>>>>>>>> for those nodes in an RDF graph that can be the subject of a >>>>>>>>>>>>> triple >>>>>>>>>>>>> in an RDF graph. But why does there have to be? One can always >>>>>>>>>>>>> say >>>>>>>>>>>>> "IRI or blank node". >>>>>>>>>>>>> >>>>>>>>>>>>> One could create such an atomic name. One might use "entity" for >>>>>>>>>>>>> this purpose. However, one should *not* use rdf:Entity, as that >>>>>>>>>>>>> would conflate the RDF theory (where one has names like >>>>>>>>>>>>> rdf:Property, rdfs:Resource, and xs:Integer) and the RDF >>>>>>>>>>>>> metatheory >>>>>>>>>>>>> (where one has names like resource, RDF graph, IRI, and >>>>>>>>>>>>> property). Well, if rdf:Entity was not an IRI, then there might >>>>>>>>>>>>> not be a conflation, but there would be other problems. >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> peter >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> On 12/22/2014 07:49 AM, Irene Polikoff wrote: >>>>>>>>>>>>>> At some point in the discussion we have agreed not to talk about >>>>>>>>>>>>>> resources when discussing RDF graphs and, instead, talk about >>>>>>>>>>>>>> nodes. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I am talking about literal nodes. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Given the following triples >>>>>>>>>>>>>> >>>>>>>>>>>>>> ex:house ex:number "2"^^xs:integer >>>>>>>>>>>>>> ex:two rdf:type xsd:Integer >>>>>>>>>>>>>> ex:house ex:number ex:two >>>>>>>>>>>>>> >>>>>>>>>>>>>> There will be two different nodes for the number 2. The first >>>>>>>>>>>>>> one >>>>>>>>>>>>>> is the literal node. The second one is an IRI node. They will >>>>>>>>>>>>>> never be the same and the graph represented by the first >>>>>>>>>>>>>> triple is >>>>>>>>>>>>>> not the same graph as the graph represented by the two last >>>>>>>>>>>>>> triples. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The fact that ex:two may stand for the "real world" resource >>>>>>>>>>>>>> that >>>>>>>>>>>>>> philosophically is the same is irrelevant here as we are talking >>>>>>>>>>>>>> about data structures and their processing. >>>>>>>>>>>>>> >>>>>>>>>>>>>> The vocabulary term that is missing is the one that >>>>>>>>>>>>>> identifies RDF >>>>>>>>>>>>>> terms that can be subjects of a triple. In the context of this >>>>>>>>>>>>>> working group, this is an important concept that needs its own >>>>>>>>>>>>>> name. I propose rdf:Entity. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Irene >>>>>>>>>>>>>> >>>>>>>>>>>>>> >>>>>>>>>>>>>> Sent from my iPhone >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On Dec 22, 2014, at 10:10 AM, "Peter F. Patel-Schneider" >>>>>>>>>>>>>>> <pfpschneider@gmail.com> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> There are a number of intertwined issues here. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Are literal values resources in RDF? Yes, a literal value >>>>>>>>>>>>>>> (e.g., >>>>>>>>>>>>>>> the number 2) is a resource. This is just abiding by the >>>>>>>>>>>>>>> principles of resources in the Semantic Web. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Can literal values have property values in RDF? Yes, a literal >>>>>>>>>>>>>>> value (e.g., the number 2) can have property values. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Can URIs denote literal values in RDF? Yes, a URI (e.g., >>>>>>>>>>>>>>> ex:two) >>>>>>>>>>>>>>> can denote a literal value (e.g., the number 2). This is just >>>>>>>>>>>>>>> abiding by the principles of IRIs in the Semantic Web. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Is it possible in RDFS to make a URI to denote a literal value >>>>>>>>>>>>>>> without causing a contradiction? Yes, via something like >>>>>>>>>>>>>>> ex:two >>>>>>>>>>>>>>> rdf:type xsd:Integer. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Is it possible in RDFS to state that some literal value has a >>>>>>>>>>>>>>> property value without causing a contradiction? Yes, via >>>>>>>>>>>>>>> something like ex:two rdf:type xsd:Integer. ex:two ex:prime >>>>>>>>>>>>>>> xsd:true. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Is it possible in RDFS to directly state that a particular >>>>>>>>>>>>>>> literal value has a property value? No, because literals >>>>>>>>>>>>>>> cannot >>>>>>>>>>>>>>> be the subject of RDF triples. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Is it possible in RDF to get close to stating that a particular >>>>>>>>>>>>>>> literal value has a property value? Yes, you can use >>>>>>>>>>>>>>> reification >>>>>>>>>>>>>>> as in _:a rdf:subject 2. _:a rdf:predicate ex:prime. _:a >>>>>>>>>>>>>>> rdf:object xsd:true. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> peter >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 12/22/2014 06:39 AM, Irene Polikoff wrote: >>>>>>>>>>>>>>>> RDF specification clearly says that there are 3 types of RDF >>>>>>>>>>>>>>>> nodes: IRI, blank node and literal. Each has its own >>>>>>>>>>>>>>>> unique/different characteristics including, for example, that >>>>>>>>>>>>>>>> literal can only be an object of a triple and blank node can't >>>>>>>>>>>>>>>> be a predicate of a triple. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I believe the specification makes it clear that these three >>>>>>>>>>>>>>>> node types are disjoint. Thus, ex:two can not be a literal >>>>>>>>>>>>>>>> node >>>>>>>>>>>>>>>> as it is an IRI. I also thought we were discussing here RDF >>>>>>>>>>>>>>>> nodes, not abstract concepts of literals. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I remember hearing that there were some discussions in the RDF >>>>>>>>>>>>>>>> working group about letting literals be subjects, but this >>>>>>>>>>>>>>>> proposal was rejected, wasn't it? >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Irene >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Sent from my iPhone >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> On Dec 22, 2014, at 8:49 AM, "Peter F. Patel-Schneider" >>>>>>>>>>>>>>>>> <pfpschneider@gmail.com> wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> On 12/22/2014 01:45 AM, ☮ elf Pavlik ☮ wrote: >>>>>>>>>>>>>>>>>>> On 12/21/2014 01:38 AM, Peter F. Patel-Schneider wrote: >>>>>>>>>>>>>>>>>>> In RDF all resources can have property values, even literal >>>>>>>>>>>>>>>>>>> values. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> peter >>>>>>>>>>>>>>>>>> Hi Peter :) >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Could you please explain it little more and if possible >>>>>>>>>>>>>>>>>> share >>>>>>>>>>>>>>>>>> links to >>>>>>>>>>>>>>>>>> relevant references? >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Thanks! >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The original version of RDF, as described in the RDF Model >>>>>>>>>>>>>>>>> and >>>>>>>>>>>>>>>>> Syntax Specification >>>>>>>>>>>>>>>>> http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/, talks >>>>>>>>>>>>>>>>> about >>>>>>>>>>>>>>>>> Resources and Literals, but does not indicate directly >>>>>>>>>>>>>>>>> whether >>>>>>>>>>>>>>>>> they are disjoint. However, there is already the idea that >>>>>>>>>>>>>>>>> anything is a resource and that anything can described by a >>>>>>>>>>>>>>>>> URI. See Section 2 >>>>>>>>>>>>>>>>> http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#basic and >>>>>>>>>>>>>>>>> Section 5 >>>>>>>>>>>>>>>>> http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#model for >>>>>>>>>>>>>>>>> more information. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The original version of RDFS, >>>>>>>>>>>>>>>>> http://www.w3.org/TR/1998/WD-rdf-schema/, which never >>>>>>>>>>>>>>>>> became a >>>>>>>>>>>>>>>>> full W3C recommendation, has the initial class hierarchy, >>>>>>>>>>>>>>>>> including rdfs:Resource, rdfs:Literal, rdfs:Class, and >>>>>>>>>>>>>>>>> rdf:Property in Figure 2. In this figure, rdfs:Resource is >>>>>>>>>>>>>>>>> the universal class, with rdfs:Class, rdf:Property, and >>>>>>>>>>>>>>>>> rdfs:Literal all as subclasses. Here is the first direct >>>>>>>>>>>>>>>>> requirement that literal values are resources. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> The first formal treatment of RDF is in RDF Semantics >>>>>>>>>>>>>>>>> http://www.w3.org/TR/2004/REC-rdf-mt-20040210/. Here >>>>>>>>>>>>>>>>> interpretations for RDF are first defined, in Section 1.3 >>>>>>>>>>>>>>>>> http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#interp, >>>>>>>>>>>>>>>>> with the >>>>>>>>>>>>>>>>> domain of an interpretation being the set of resources and a >>>>>>>>>>>>>>>>> subset of the resources being literal values, as in the >>>>>>>>>>>>>>>>> original version of RDFS. Properties are another subset >>>>>>>>>>>>>>>>> of the >>>>>>>>>>>>>>>>> resources, which are linked to their extent, which is a >>>>>>>>>>>>>>>>> set of >>>>>>>>>>>>>>>>> pairs over the resources. There is no requirement here that >>>>>>>>>>>>>>>>> literals cannot be the first element of a property pair. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> One might argue that the formal treatment is a misreading of >>>>>>>>>>>>>>>>> the informal 1999 description of RDF, but the ability for >>>>>>>>>>>>>>>>> literals to have property values has definitely been in RDF >>>>>>>>>>>>>>>>> since at least 2004. This stance is also consistent with the >>>>>>>>>>>>>>>>> dictum that URIs can identify anything, which includes >>>>>>>>>>>>>>>>> literal >>>>>>>>>>>>>>>>> values. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> For example, one can say in RDF >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> ex:two rdf:type xsd:Integer . >>>>>>>>>>>>>>>>> ex:two ex:prime xsd:true . >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Peter F. Patel-Schneider >>>>>>>>>>>>>>>>> Nuance Communications >>>> >>>> > >
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