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Re: Applying Postel's Law to HTML Data

From: Ivan Herman <ivan@w3.org>
Date: Thu, 6 Oct 2011 06:18:44 +0200
Cc: public-html-data-tf@w3.org
Message-Id: <A078601B-AD78-4941-B28D-F9430B020172@w3.org>
To: Jeni Tennison <jeni@jenitennison.com>

interesting coincidence, I was remember the same law a few days ago related to this issue...

On Oct 6, 2011, at 24:32 , Jeni Tennison wrote:

> Hi,
> Postel's law states [1]:
>  "Be conservative in what you send; be liberal in what you accept."
> To what extent does it make sense to have this as a guideline for HTML data? Should we recommend that consumers of data from HTML pages try to accept all data formats, and that publishers should publish in only one to simplify their markup?

I think both statements are very reasonable.

> There are a few examples where consumers are being liberal: Google Rich Snippets now uses both microdata and RDFa that uses the schema.org vocabulary [2], as well as various other vocabularies and microformats; Sindice [3] parses out RDFa, microdata and microformats. But there are also many examples of consumers and tools that are targeted towards one particular syntax -- I'm thinking of OGP from Facebook [4], various validators, browser plug-ins and Javascript libraries.
> If consumers aren't liberal it's hard for publishers to be conservative. Should we encourage/anticipate people publishing in multiple formats with the same vocabulary to target different consumers? Publishing the same data in different vocabularies and different formats? Using different formats for different kinds of data or in different parts of the page?

If we take those two statements above, I think what this means is that we should encourage authors to publish in one forma of their choice only. There may be cases when authors would end up mixing syntaxes, eg, when doing some cut and paste from various places (although transformation tools may help them in this), so it should be allowed and made possible; nevertheless, if we issue guidelines then I think we should certainly advocate a single syntax per page approach whenever possible. Even if consumers are liberal in what they consume (and they should be) a single syntax per page makes a site more readable, manageable, etc.

Note that this is only one side of the coin. The other side is how liberal consumers should be when accepting malformed data in a particular syntax. That is a very different ballgame.



> What do you think?
> Jeni
> [1]: http://en.wikipedia.org/wiki/Robustness_principle
> [2]: http://www.google.com/webmasters/tools/richsnippets?url=http%3A%2F%2Fschema.openspring.net%2Fnode%2F3&view=cse
> [3]: http://inspector.sindice.com/index.jsp
> [4]: http://developers.facebook.com/docs/beta/opengraph/objects/
> -- 
> Jeni Tennison
> http://www.jenitennison.com

Ivan Herman, W3C Semantic Web Activity Lead
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Received on Thursday, 6 October 2011 04:17:40 UTC

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