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Re: [giles@ontv.com: Nesting of data structures]

From: Lorrie Cranor <lorrie@research.att.com>
Date: Thu, 26 Apr 2001 10:26:01 -0400
Message-ID: <01e101c0ce5d$0f7c0400$9816cf87@barbaloot>
To: "Giles Hogben" <giles@ontv.com>
Cc: <www-p3p-public-comments@w3.org>
> I am writing a P3P User Agent implementation following the W3 spec as
closely as possible

Glad to hear it. Please keep us posted on your progress and let us
know if you release your software publically. You may also want to join
the P3P developer's mailing list if you haven't already done so. Please
see http://www.w3.org/P3P/develop.html

> and I have a question on the P3P spec relating to the following sentence:
> "Note that in any case there MUST NOT be more than one data schema per
file (so, care should be taken when embedding a data schema in a POLICY
contained in a POLICIES element). "

What this means is there cannot be more than one <DATASCHEMA> element in
a file, because we don't currently have a way of referring to this element
except by the
name of the file that contains it. A policy can refer to many different
contained in many different files.

> It is not clear from this whether there must be no external references in
the one data schema allowed:
> It is clear that references to the base data schema of the form
> structref="http://www.w3.org/TR/P3P/base#postal"
> are allowed
> But how about external references such as
> structref="http://www.myDataschemabase.org/schema1.xml#structure"

Yes, that is allowed too.

> I would also be interested to know why the name=CATa.CATb.CATc
stuctref="CATd" format (which is essentially relational) was chosen for
expressing these structures, rather than an xml based format such as
> <CATa><CATb><CATc><CATd></CATd></CATc></CATb></CATa>
> which is hierarchical

The dot notation was adopted about 4 years ago for reasons I can't remember.
More recently we changed it slightly to make it a URI, at the request of
the CC/PP working group. The existing dot notation lends itself well to
As you have discovered, the data schemas are in fact hierarchical, but
are being expressed with this flat notation rather than an xml format. But
anyone who wants to represent them in an xml format inside their
can certainly do that.

Lorrie Cranor
P3P Specification Working Group Chair
Received on Thursday, 26 April 2001 10:32:46 UTC

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