- From: pat hayes <phayes@ai.uwf.edu>
- Date: Tue, 11 Sep 2001 13:35:35 -0500
- To: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
- Cc: w3c-rdfcore-wg@w3.org
>At 01:52 AM 9/11/01 +0100, pat hayes wrote: >>Oh dear. That simply does not make sense. Look, there are two notions here. >>One is the thing with an identity, more traditionally called the thing >>denoted; examples include web sites, books, human beings, corporations, etc. >>. Another is the conceptual mapping or correspondence between the name and >>that first thing, sometimes called the denotation mapping. These are not, >>and cannot possibly be, the same thing. So RFC2396 is just plain confused. > >[Full message below] > >Oh dear, indeed ;-) > >I'll not try and respond directly to your points (yet), but see if I >can skirt around them.. > > >Problem statement: > >The web currently contains many things, identified by URIs, that >correspond to ideas like "the current weather". I think this is >something that makes the web truly valuable -- the ability to >deliver dynamic information. If RDF cannot describe these things >then I think it falls very short of the goal to be able to describe >all things that are "on the Web". I've never beleived for a second that RDF can describe all the things that are on the web. RDF is really a very, very small language with very limited expressiveness. It isn't a miracle cure for the whole of semiotics. > >Some tangential background: > >One of the challenges of functional programming, in its strictest >form in which all values are immutable, is its use in applications >that deal with inherrently dynamic things (text editors, real-time >control, etc.). The approach that I have seen adopted is to treat >such things as sequences of values, or time-varying functions. >Coupled with techniques like lazy evaluation that only evaluate >values as they are required, a program can represent and handle such >possibly-infinite values. Right, continuations and that kind of thi ng. >Possible solution? > >(This may be a horrible abuse of a new trick, but I must try...) > >The functional programming trick seems not dissimilar to the >relational-extension trick used in the MT denotation of RDF >predicates. Can it also be applied to the denotation of resources? > >So, a "resource" is the thing identified by a URI. Why not have the >idea of a resource extension that corresponds to the set of entities >that can be retrieved via a resource, where each entity is a static >sequence of octet data? But there is something basically wrong with that picture. Entities (and resources) are *not* streams of octet or any other data, in general: they can be real solid things like books and people. (This may be tangential to your main point.) >(At this stage, for the purpose of testing the resource extension >idea, I've deliberately stuck to things that can actually be >retrieved on the web, and left unspecified any correspondence there >may be between the data and other real-world objects.) As I understand it, the real-world objects *are* resources, so the idea of being retrievable on the web simply isn't applicable to resources in general. > Then, the resource can correspond to the current weather forecast, >but its extension includes the set of all weather forecasts for all >times; the particular member of that extension one retrieves >depends on when the retrieval is performed. We could do something like this, but this is what I meant by a modal (possible-world) semantics, since the denotation here ought to be not the entire extension (in your extended sense) but the particular member of it at the time the query was made. The semantics on this case would need to introduce a notion of times and time-relations in order to make snes eof this notion of 'now'. (It could be a very simple notion, eg points with a total order, but the point is that we would need to say *something* about it.) In the meantime however we could also just put this issue off to the future, and the current MT be thought of as kind of instantaneous time-slice of this extended temporal semantics. >It seems to me that this treatment of resources is allowed by, and >orthogonal to the current model theory, because it still provides a >fixed denotation for each URI, just one a that is more complex than >originally envisaged. It also seems, to me, to capture something of >the intent of RFC2396. I wonder what the intent of RFC2396 actually was, I have to confess. It just seems to me to be confused. >#g >-- > >At 01:52 AM 9/11/01 +0100, pat hayes wrote: >> > >> > This is true -- Though RFC2396 does draw a clear distinction between >> > "resource" and "entity": >> > >> > Resource >> > A resource can be anything that has identity. Familiar >> > examples include an electronic document, an image, a service >> > (e.g., "today's weather report for Los Angeles"), and a >> > collection of other resources. Not all resources are network >> > "retrievable"; e.g., human beings, corporations, and bound >> > books in a library can also be considered resources. >> > >> > The resource is the conceptual mapping to an entity or set of >> > entities, not necessarily the entity which corresponds to that >> > mapping at any particular instance in time. Thus, a resource >> > can remain constant even when its content---the entities to >> > which it currently corresponds---changes over time, provided >> > that the conceptual mapping is not changed in the process. >> > >> > >>Oh dear. That simply does not make sense. Look, there are two notions here. >>One is the thing with an identity, more traditionally called the thing >>denoted; examples include web sites, books, human beings, corporations, etc. >>. Another is the conceptual mapping or correspondence between the name and >>that first thing, sometimes called the denotation mapping. These are not, >>and cannot possibly be, the same thing. So RFC2396 is just plain confused. >> >>BTW, it is even more confused that this, since neither of these notions >>(entity denoted and denotation mapping) have got anything particularly to do >>with time and change, and the introduction of a temporal distinction in the >>second paragraph seems to confuse denotation - the mapping from a >>representing or naming symbol to the thing it denotes or names - with some >>notion of a temporally unchanging referent which somehow 'corresponds' >>(whatever that means) to a changing value. The phrasing " the entity which >>corresponds to that mapping at any particular instance in time" is >>incoherent and meaningless. The last sentence is nonsense: if the thing >>identified by the mapping changes, then *of course* the mapping has changed, >>since the mapping *is* the relationship between the names (or referring >>expressions) and the things 'identified' by the mapping.. >> >>I don't think there is any point it trying to 'rescue' this prose. It is too >>broken to be useful. >> >> >> > Hence, I have a problem with: >> > >> > >> > Resource >> > >> > The universe in which RDF operates is seen as a >> > potentially huge collection of `resources'. >> > >> > >> > Resources are the identifiable items in the world, >> > the contact points between you and the world of data. They are `entities' >> > as we need to refer to them, fixed for a short time while we talk about >> > them. >> > >> > >> > >> > I think it is important to keep the clear distinction between "resource" >> > and "entity" so that resources like "the current weather report" don't tie >> > us up in knots. >> > >> > >>They are already tied up in knots. That phrase is meaningless in an >>extensional language, since it has an implicit "now" in it, which is an >>indexical. If URIs have an implicit reference to the time of use built into >>their meaning, then *any* model theory for *any* language which uses URIs >>will need to be based on something like a modal semantics which explicitly >>mentions temporally possible worlds. That could be done, but it gets us into >>a minefield of complexity (what kind of temporal model do we assume? >>Discrete or continuous? Based on points or intervals? Deterministic or >>branching? Etc.) >> >>The RDF model theory as it stands simply does not support the notion of an >>URI meaning 'the current weather report'. There is no notion of 'current' >>or 'now' or 'at the time of accessing' in the semantics. At any given >>moment, a URI might denote the weather report at that moment, but if that >>gets changed then the meaning of the URI gets changed as well. Changing the >>content of a weather-report URI is a genuine change, not merely an update to >>an ongoing temporally-relative 'tensed' meaning. >> >> >> >> >> >> > A typical resource would be a unit of data on the >> > Web such as a page or a significant segment of a page. Equally another >> > person, an organization or anything else that you would wish to point at >> > out there in this universe can be referred to as a `resource'. The >> > significant characteristic is the identifiable nature of resources, that >> > they have for whatever period of time an identity which makes them >> > distinguishable. >> > >> > >> > [RDFT&C] May refer to an RDF resource or a Web >> > Resource. Some resources may be both. In discussion of RDF, this term is >> > often used to mean RDF Resource. >> > [RDFM&S:introduction] >> > A resource may be an entire Web page; such as the >> > HTML document "http://www.w3.org/Overview.html" for example. A resource >> > may be a part of a Web page; e.g. a specific HTML or XML element within >> > the document source. A resource may also be a whole collection of pages; >> > e.g. an entire Web site. A resource may also be an object that is not >> > directly accessible via the Web; e.g. a printed book. Resources are always >> > named by URIs plus optional anchor ids (see [URI]). Anything can have a >> > URI; the extensibility of URIs allows the introduction of identifiers for >> > any entity imaginable. >> > >> > >> > [RDFM&S:glossary] >> > An abstract object that represents either a >> > physical object such as a person or a book or a conceptual object such as >> > a color or the class of things that have colors. Web pages are usually >> > considered to be physical objects, but the distinction between physical >> > and conceptual or abstract objects is not important to RDF. A resource can >> > also be a component of a larger object; for example, a resource can >> > represent a specific person's left hand or a specific paragraph out of a >> > document. As used in this specification, the term resource refers to the >> > whole of an object if the URI does not contain a fragment (anchor) id or >> > to the specific subunit named by the fragment or anchor id. >> > >> > >> > [Jena] Some entity. It could be a web resource such >> > as web page, or it could be a concrete physical thing such as a tree or a >> > car. It could be an abstract idea such as chess or football. Resources are >> > named by URIs. >> > >> > >> > [N3] That identified by a Universal Resource >> > Identifier (without a "#"). If the URI starts "http:", then the resource >> > is some form of generic document. >> > >> > Web Resource >> > >> > Resources which have their identity by nature of >> > their accessibility on the World Wide Web are sometimes distinguished as >> > `Web Resources'. To make this identification, we may have to chose one >> > aspect of this entity's contact with the Web - for an organization: a >> > particular Web page, for a person: an email account, etc. >> > [RDFT&C] >> > Anything that is identified by a URI >> > >> > >> > >> > Further ammunition for the distinction between an RDF resource and a web >> > resource: >> > >> > [[[ >> > When making a reference, such as a hypertext link, we don't just refer to >> > a >> > resource. Well, we can, but we can also refer to a particular part of or >> > view >> > of a resource. >> > >> > >>Oh dear. That also doesn't make sense to me. What does it mean to refer to a >>'particular view' of something, rather than refer to it? >> >> >> > The string which, within the document, defines the other end of >> > the link has two parts. It has the identifier of the document as a whole, >> > >> > >> > >>So a URI is an identifier of a *document* ?? But I thought that we were >>working on the understanding that URIs denote *things*, not just documents. >> >> >> >> > and >> > then optionally it has a hash sign "#" and a string representing the view >> > of >> > the object required. This suffix is called a fragment identifier. (Even >> > though it doesn't represent necessarily a fragment of the document: it >> > could >> > represent how the document should be viewed.) >> > >> > >>How about representing things that have nothing to do wth documents? >> >> >> > ]]] >> > -- http://www.w3.org/DesignIssues/Model.html >> > >> > [[[ >> > Fragment identifiers for RDF identify concepts >> > >> > The semantic web has information about anything. The fragment identifier >> > on >> > an RDF (or N3) document identifies not a part of the document, but >> > whatever >> > thing, abstract or concrete, animate or innanimate, the document describes >> > as >> > having that identifier. >> > >> > >>Which flatly contradicts the previous quote. Sigh. >> >>Pat >>--------------------------------------------------------------------- >>(650)859 6569 w >>(650)494 3973 h (until September) >>phayes@ai.uwf.edu >>http://www.coginst.uwf.edu/~phayes >> >>This footnote confirms that this email message has been swept by MIMEsweeper >>for the presence of computer viruses. > >------------------------------------------------------------ >Graham Klyne MIMEsweeper Group >Strategic Research <http://www.mimesweeper.com> ><Graham.Klyne@MIMEsweeper.com> >------------------------------------------------------------ --------------------------------------------------------------------- (650)859 6569 w (650)494 3973 h (until September) phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Tuesday, 11 September 2001 12:34:12 UTC