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RE: [DI Glossary] DeliveryUunit

From: Rotan Hanrahan <Rotan.Hanrahan@MobileAware.com>
Date: Thu, 18 Aug 2005 15:24:50 +0100
Message-ID: <D9BC812593BC2E44A803E6765FFA5E2D92D20A@gpo.mobileaware.com>
To: "Johannes Koch" <koch@w3development.de>, <www-di@w3.org>

There are direct responses and indirect responses. The direct response to a user-initiated request (conveyed via HTTP) is typically a markup document. (It might be an image, but that direct response is a trivial case.) As a consequence of the markup, the browser may identify the need for further resources, such as stylesheets, scripts or media items. These are identified by the browser without any specific need for interaction by the user. The presentation, for which the browser is responsible, could not be rendered without these identified resources. Consequently there are indirect requests, subsequent to the original request initiated by the user. These indirect requests result in the provision of the associated resources (CSS, JS, images etc.) and when all of these have been delivered, the browser is finally capable of rendering the presentation.

The "set of material" has been delivered as a response to the original (direct) request.

Part of the problem you have raised is that the definition does not explain anything with respect to the cause of HTTP requests. It merely defines a Delivery Unit as being whatever is transferred as a response to a single HTTP request, which strictly includes the user-initiated HTTP request *and* the subsequent requests made by the browser. Typically, each response contains just one item of material (a markup document, a script, a stylesheet, an image etc.). Thus the phrase "set of material" would appear to be at odds with the rest of the definition. However, if you accept that the subsequent requests by the browser are really caused by the initial request, then the subsequent responses are also (indirectly) responses to the original request. In this interpretation, the phrase "set of material" makes sense.

The DI Glossary is a live document. Where improvements are identified, updates can be made. The structure of the DI Glossary permits such updates while ensuring that previous definitions can remain valid in the context in which they were referenced.

---Rotan


-----Original Message-----
From: Johannes Koch [mailto:koch@w3development.de]
Sent: 18 August 2005 15:01
To: www-di@w3.org
Subject: [DI Glossary] DeliveryUunit



The DI glossary defines "Delivery Unit" as

     A set of material transferred between two cooperating web programs
     as the response to a single HTTP request. The transfer might, for
     example, be between an origin server and a user agent.
     Users are not normally aware of individual delivery units.

(<http://www.w3.org/TR/di-gloss/#def-delivery-unit>)

So this cannot mean an (X)HTML document plus the referenced images, 
scripts, style sheets, etc, because they are retrieved by different HTTP 
requests each. So what is a delivery unit then?
-- 
Johannes Koch
In te domine speravi; non confundar in aeternum.
                             (Te Deum, 4th cent.)
Received on Thursday, 18 August 2005 14:25:23 UTC

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