At 05:14 PM 9/5/01 +0200, Martyn Horner wrote:

An RDF Glossary


[...]
Entity
The world (and the world of information that it encloses) contains a vast number of `entities' - things we talk about and think about. Many have names and words in human languages, some have no name but can be referred to in passing.
[RDFT&C]
Anything which exists or has existed. Note that RFC2396 uses this term in a more restricted sense, to mean some data represents some aspect of a Web Resource.

[MH] Actually [RFC2396] doesn't attempt to define `entity'.

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.

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.
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. 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, 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.)
]]]
 -- 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.

It is important, on the  Semantic Web, to be clear about what is
identified. An http: URI (without fragment identifier)
necessarily identifies a generic document. This is
because the HTTP server response about a URI can deleiver a rendition of (or
location of, or apologies for) a document which is identified by the URI
requested.  A client which understands the http: protocol can immediately
conclude that the fragementid-less URI is a generic document.  This is true
even if the publisher (owner of the DNS name) has decided not to run a server.
Even if it just records the fact that the document is not available online,
still a client knows it refers to a document.  This means that identifiers for
arbitrary RDF concepts should have fragment identifiers.  This in term means
that RDF namespaces should end with "#".
]]]
 -- http://www.w3.org/DesignIssues/Fragment.html

I find it difficult to unify the RDF idea of a resource (a thing that is identified) with the general Web idea of a resource (a thing that is queried or accessed) in light of these comments.  Hence, for now, I draw the distinction.
[Dan Connolly (email)] Nope; that rules out real numbers...

[Accessibility] anything that has identity on the Web. A Web resource is identified by a URI.

[WebChar] A resource, identified by a URI, that is a member of the Web Core (The collection of resources residing on the Internet that can be accessed using any implemented version of HTTP as part of the protocol stack (or its equivalent), either directly or via an intermediary. Notes: By the term "or its equivalent" we consider any version of HTTP that is currently implemented as well as any new standards which may replace HTTP (HTTP-NG, for example). Also, we include any protocol stack including HTTP at any level, for example HTTP running over SSL.).

[RFC2616] A network data object or service that can be identified by a URI, as defined in section 3.2. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or vary in other ways.

[RFC2396 (in context of defining URI)] 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


I think those are probably the biggest concepts to be nailed.

#g