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text about server metadata being in sync with reality

From: Tim Berners-Lee <timbl@w3.org>
Date: Tue, 10 Aug 2004 12:38:29 -0400
Message-Id: <B57D4FF3-EAEB-11D8-A9E8-000A9580D8C0@w3.org>
To: 'www-tag@w3.org' <www-tag@w3.org>

The accuracy of metadata is relies on the server administrator and the 
author of documents, and the software that they use. Practically, the 
capabilities of the
tools and the social relationships may be the limiting factors. For 
example,

Expiry Date:  It is important that Expiry Date on documents be set 
accurately to allow caches to refresh, not wasting bandwidth, but 
avoiding stale data.
The author (rather than the webmaster) will often be the authority
on what the actual expiry date, or likely lifetime,  of a document is.
However, if the author has does not go to the trouble of thinking about 
and setting the expiry date explicitly, then the server may be in a 
position to guess as a function of the time since the document was last 
edited.

Character encoding: The client editing software is in the best position 
to know what character encoding was  used for a document.  In the case 
of XML documents, the encoding can be deduced by reading the document, 
so the server software can ensure that the correct metadata is sent by 
sensing it (dynamically or statically).  Other techniques vary from 
insisting on a particular encoding (and checking validity) for all 
files; or allowing a user interface to specify the encoding, or using a 
filename convention.

Content type:  This is often managed by a site-wide filename 
convention, such as mapping "*.html" to application/html+xml. This can 
be a problem as it makes it difficult to introduce new types, and users 
may have other constraints on filenames from other tools.
Webmasters should allow local user control of content-type generation, 
so that new Internet Media Types can be introduced.  A common problem 
is that new forms of data (e.g. Java programs or Speech dialogs) end up 
being served as text/plain by default, and this prevents client systems 
to treat the data appropriately.  This also prevents future migration 
of the information from the existing content type to a new type in the 
future. Solutions include local metadata files, and user metadata 
control forms.

In all cases the accuracy of  these and other metadata is just as 
important for dynamic web resources, where a little bit of thought and 
programming can ensure the correct metadata for a huge number of 
resources.
__________________
Received on Tuesday, 10 August 2004 16:38:34 GMT

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