Public Identifiers

Michael Kay M.H.Kay at
Fri Sep 18 16:00:58 BST 1998

>> I'm wondering if there is any standardization of what's
in a "public
>> identifier"
>The SGML standard (ISO 8879) defines something called a
'formal public
>identifier' (clause 10.2), but whether public identifiers
must be FPIs
>or not is defined by the SGML declaration used.
>In other words: public identifiers can be whatever you
want, but you
>can declare them to be FPIs.

I think this response is referring to SGML rather than XML.
There is no SGML declaration in XML. There is no normative
link between XML and SGML, and therefore no normative link
between XML Public Identifiers and SGML FPIs.

XML does not require a Public Identifier to be either public
or an identifier; you can put anything in there that you
like, and it has no defined meaning. Tim Bray's annotated
XMl spec (on has this to say:

... public identifiers are a trick inherited from SGML that
are probably only useful to people who already have working
SGML software installed. Remember that if you use public
identifiers within your own organization, that's perfectly
OK, but if you want to interchange XML documents with
anybody external, they have the right to demand, and you
have the obligation to provide, a working system identifier
(URI) for each external entity.

Mike Kay

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