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Re: HTTP 1.1 document terminology (suggestions)

From: John Franks <john@math.nwu.edu>
Date: Mon, 29 Apr 1996 13:51:48 -0500 (CDT)
To: jg@w3.org
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <Pine.SUN.3.91.960429125959.14342A-100000@hopf.math.nwu.edu>
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/379
On Mon, 29 Apr 1996 jg@w3.org wrote:

> As you all know, we've had terminology problems that has caused much
> anguish, where different people have had slightly different views of
> what the same term means (and those people then ended up generating
> new terminology to compensate).  We only recently figured out this 
> disconnect was the cause of much of the anguish of the last month.
> The terms "resource", "variant", "entity", "entity instance" were being
> used in sloppy ways (and as there are only three things to be described,
> the fact we were using four is a fundamental sign of the problem).
> It would help the discussions to try to be precise in terminology.

Jim, I think you have made a great deal of progress on this important
task.  Just how important it is has become clear because of the 
difficulties we have had.

I have a few suggestions for your consideration.  Things marked with
'>' a the beginning of a line have not been changed, i.e. the "entity"
definition is unchanged but I would suggest moving it ahead of the other
definitions.  Comments or questions are marked with "###".

> entity
> ------
> The set of information transferred as the payload of a request or
> response.  An entity consists of metainformation in the form of
> Entity-Header fields and content in the form of an Entity-Body, as
> described in section 11 


A network data object or service that can be identified by a URI
(section 7.2). A "resource" is a concept (a little like a Platonic
ideal).  In general a resource may correspond to a single entity or to
many entities.  These entities could exist simultaneously, or
serially, or both.  The resource may include entities which will only
exist in the future.  The defining characteristic that unites these
entities in a resource is the sharing of a common URI.

specific resource

A resource may be of the kind which corresponds to only one possible
octet stream representation.  An example is the text version of an
Internet RFC. That never changes. It will always have the same
checksum.  Such a resource corresponds to only one entity and is
called a specific resource.

### Question: Is this what a specific resource should be, or should it
### be something like a homepage which only has one representation at
### a time?  If the definition above is correct then specific
### resources are rather rare.  We might want to use specific resource
### to mean a resource that has only one representation at a time.  It
### could be called a "serial resource."

generic resource

On the other hand, a resource may be generic in that as a concept it
is well specified but not so specifically specified that it can only
be represented by a single octet stream.  Such a resource corresponds
to multiple entities or potential entities.  Other URIs may or may
not exist which identify a resource more specifically. These other
URIs identify resources too, and there is a relationship of genericity
between the generic and the relatively specific resource.  As an
example, successively specific resources might be
> 1. The Bible
> 2. The Bible, King James Version
> 3. The Bible, KJV, in English
> 4. A particular ASCII rendering of the KJV Bible in English
> [continue as in original]


> variant
> -------
> A specific resource that is a member of at least one generic
> resource.  Sometimes called a resource variant.  Note that the set of
> variants of a generic resource may change over time as well.

### There are two reasons calling a variant a "specific resource"
### seems problematic to me.  1) Every resource should have a URI, but
### a variant may not (unless I misunderstand) e.g. a resource may
### have a French and English version determined by content
### negotiation.  These are variants, but there need not be a URI for
### just the French version.  2) A variant corresponds to something
### like "the French version" so it can change with time.  It would
### make sense for a variant to be a "serial resource," but not a
### specific resource.

> resource entity
> ---------------
> A particular representation, rendition,
> encoding, or presentation of a resource at a particular point in time.
> Resources not supporting content negotiation are bound to a single
> entity.  Generic resources supporting content negotiation are bound to
> a set of one or more entities, whose membership may vary over time.

### I don't understand why this term is needed.  Is there such a thing
### as an entity which is not a resource entity?

John Franks 	Dept of Math. Northwestern University
Received on Monday, 29 April 1996 11:57:00 UTC

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