xml-dev - Re: Notations

["James Tauber" <jtauber@jtauber.com>]

>> From: W. Eliot Kimber
>> Remember that notations do not affect the *parsing* of the data, only its
>> semantic interpretation.
>
>If that is so, I am back to square zero in my understanding of notations!
>
>For example, I thought that if I wanted to put MIDI data in an XML
document,
>I would use notations to the indicate the fact. But I can't semantically
>interpret MIDI data (or even hear the music) before I've parsed it. The
>notation is surely there to tell me that it's MIDI, not that it's Vivaldi.

By "not affect[ing] the *parsing of the data", I think Eliot means the
parsing by an XML processor. The point is that NOTATIONs say nothing about
how an XML processor is to treat the character data. They are about helping
an application interpret the syntax of the character data.

As I've discovered before on this list, there can be a lot of confusion in
the use of the term "semantic[s]". I think this is partly because you need
to know what layer you are talking about.

At the token level, XML specifies both a syntax and a semantics. (eg it
tells you where '<' can occur and tells you want it means when it does).

But the semantics at this level are purely to provide the syntax for the
next.

At the element level, XML optionally specifies a syntax (via a DTD) but
*not* a semantics. (eg it tells you where 'Price' can occur but not what it
means).

At the application layer, it's different again.

At one level, element types could be viewed as providing semantic labelling
of data and notations as providing syntactic labelling, eg

<song format="MIDI">...</song>
(where format is a notation attribute)

Elements, with their name, generally express an isa relationship between
element type and content.
Attributes, generally express a hasa relationship between properties and
content.
Notations, say something about how the syntax of the content is to be
interpreted by some separate application.

But even though notations are about syntax, they aren't about XML token
syntax, or XML element syntax. In as much as notations help an application
*INTERPRET*, they are providing a form of semantics. It is semantics leading
to how to subsequently parse the syntax of the character data.

Remember: One application's semantics is another's syntax. :-)

James
--
James Tauber / jtauber@jtauber.com / www.jtauber.com
Associate Researcher, Electronic Commerce Network
Curtin University of Technology, Perth, Western Australia

Maintainer of : www.xmlinfo.com,  www.xmlsoftware.com and www.schema.net





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