Re: Definitions: caches, history buffers, etc.

David W. Morris:
>
>
>
>On Tue, 9 Jan 1996, Koen Holtman wrote:
>
>>    history buffer
>> 
>>        A user agent's local store containing entities retrieved
>>        earlier in a session, and the subsystem that controls its
>>        entity storage, retrieval, and deletion.  User agent history
>>        mechanisms, such as "Back" buttons and history lists,
>>        preferably use, but are not limited to using, a history buffer
>>        to redisplay entities retrieved earlier.  Though a history
>>        buffer may share memory with a cache, its entity storage,
>>        retrieval, and deletion subsystem is usually different from the
>>        control subsystem of a cache.
>
>I'm afraid that the distinction is to steril in that it lacks any
>motivating reason for the distinction.

This is by design: I don't think that the terminology section should
contain motivations for the need to define some terms.

> We need to be clear about why
>it is important to have a distinction. I don't have alternative words
>yet but will mull it over.

If you want some raw material for writing for a motivation, here is
the relevant section from http://www.amazon.com/expires-report.html.
I particularly like the last paragraph.

 | UNCOUPLING CACHE AND HISTORY
 | 
 | It should by now be clear that history functions that always reload
 | expired pages are a bad thing.  For the majority of applications, it
 | is perfectly OK for history functions to redisplay an expired copy of
 | a resource: the main requirement for history functions is that they
 | are fast, not that they are up to date.
 | 
 | In fact, it could even argued that displaying the expired copy instead
 | of a fresh copy is preferable.  This allows a user to review the
 | previous contents of a dynamic resource, e.g. the stock quotes 5
 | minutes ago, or to review user-supplied information in previously
 | submitted dynamic forms.
 | 
 | If a resource is explicitly requested by clicking a link or submitting
 | a form, it is *never* acceptable to display an expired copy: the main
 | requirement for this type of access, which can go through a cache, is
 | that it produces up to date results, not that it is fast.
 | 
 | Though a cache and a history buffer may share memory for non-dynamic
 | pages and pages that have not yet expired, they are two different
 | kinds of store, with different requirements.  A cache may never serve
 | an expired copy, a history buffer can even hold multiple different
 | expired copies of the same resource (for example, the price of Apple
 | Computer stock every 5 minutes for the past hour).

>Dave Morris

Koen.

Received on Wednesday, 10 January 1996 12:10:08 UTC