i109: Clarify entity / representation / variant terminology

<http://www3.tools.ietf.org/wg/httpbis/trac/ticket/109>

The following three terms are defined in 2616:
> entity
>
> The 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 7.
>
> representation
>
> An entity included with a response that is subject to content  
> negotiation, as described in section 12. There may exist multiple  
> representations associated with a particular response status.
>
> variant
>
> A resource may have one, or more than one, representation(s)  
> associated with it at any given instant. Each of these  
> representations is termed a 'varriant'. Use of the term 'variant'  
> does not necessarily imply that the resource is subject to content  
> negotiation.
>


It's been asserted that there's no real distinction between these  
terms (keeping in mind that the distinction between "a particular  
instance of an entity/representation/variant" and "the entity/ 
representation/variant that might be seen under particular  
circumstances" is a separate issue, #69).

If we can agree on that, we only need to find a way to rationalise the  
terms in the spec.

Straw-man proposal:

1) "variant" occurs 16 times in the -02 specs, and a good portion of  
those is the "requested variant" text. If we ignore those instances  
for the moment, the expedient thing to do would seem to be to change  
the remaining occurrences to either "entity" or "representation," and  
remove this term altogether.

2) "representation" occurs 47 times in the -02 specs, while "entity"  
occurs 420 times.

One option would be to switch all occurrences of "entity" over to  
"representation" or vice-versa. If we do the former, we'll end up with  
awkward things like changing the classification of "entity-header  
fields" to "representation-header fields" and "entity tags" to  
"representation tags." Doing the latter seems more straightforward,  
but it still jars some.

A more moderate approach to #2 would be to choose a preferred term,  
migrate to it where it's sensible (at editors' discretion), and  
explicitly define the terms to mean the same thing.

Thoughts?


--
Mark Nottingham     http://www.mnot.net/