What are XML's namespaces?

W. Eliot Kimber eliot at isogen.com
Mon Apr 21 14:38:48 BST 1997

At 07:15 PM 4/20/97 -0400, Eric Baatz - Sun Microsystems Labs BOS wrote:
>I didn't notice any mention in the April Draft of XML having one or
>more namespaces.  By that I mean if element names and attribute
>names share the same namespace then I can't have an element with
>the same name as an attribute.  I suspect that the answer is
>"just like SGML," but I'm deathly ignorant of SGML, so I need
>a layman's explanation or a narrowly focused pointer into a
>document about SGML that I can borrow or find on the Web.

The full set of name spaces in SGML is defined in the SGML property set,
first published in the DSSSL standard (see www.jclark.com for an electronic
copy) and soon to be re-published, slightly revised, in the HyTime standard.

The primary name spaces in SGML are:

o Element types: unique within a document
o General entity names: unique within a document
o Parameter entity names: unique within a document
o Element IDs: unique within a document
o Notation names: unique within a document
o Attributes: unique within an element type
o Name groups as attribute value prescriptions: Unique within an element
  type (today), soon to be unique within an attribute w/in an element type

All names except entity names are not case sensitive in the reference
concrete syntax.

Note that architectures and applications could define additional name
spaces by defining either extensions to the SGML property set (as HyTime
does) or their own semantic property set (as HyTime also does) in which
additional name space properties are defined.

As a resource for further investigation, you may find the
recently-published "The Concise SGML Companion", by Neil Bradley to be
useful.  It provides a compact and very accessible reference to the SGML
standard.  I found it to be very accurate (I only found a few errors of
fact, and most of those were quibles that only SGML wonks like me would
care about).  ISBN 0-201-41999-9, 29.95 Dollars US, Addison Wesley.



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