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SD5 - Namespaces

From: Jean Paoli <jeanpa@microsoft.com>
Date: Thu, 15 May 1997 21:14:20 -0700
Message-ID: <78DFE33066ABD0118B9200805FD431BA5EC14D@RED-16-MSG.dns.microsoft.com>
To: "'w3c-sgml-wg@w3.org'" <w3c-sgml-wg@w3.org>
SD5 - Namespaces:
-----------------------------

Consumers of a document may need to verify that it uses a known
namespace. For 
example, the document may declare, in effect, "This is an OSF banking
document. 
If you know what that means, this is confirmation you have the right
document 
type." We need a mechanism for identifying schemata so readers of a
document can 
tell what the element names mean. At the same time, the namespace of
schema ids 
must be open and unlimitedly extensible, without requiring any central
naming 
authority (beyond whatever mechanisms already exist for the web).

Additionally, we want to make it common that documents incorporate
elements and 
attributes from multiple schemata. For instance, within a document about
book 
orders, we might reasonably find elements such as "author" defined by
the Dublin 
Core, other elements such as "price" that are particular to the book
order 
application, and still other elements, such as digital signatures,
common to 
many applications. (One advantage of common terms is that we can pass
elements 
across organizational boundaries.)

However, there is a problem with including names from multiple schemata:
common, 
easily understood terms such as "name," "type," "size," "location" etc.
are 
likely to be defined in many schemata. While each definition makes sense
in the 
context of the defining schema, when a document uses several schemata
the names 
will clash (if not initially, then as schemata evolve). We need a
mechanism for 
avoiding such conflicts. Within every portion of a document, it must be 
unambiguous from which namespace each name originates.

Proposal: Every element comes from some schema, which becomes the
default schema 
for that element. The names within the default schema are usable within
the 
element without qualification. Names from other schemata are also usable

(provided they are compatible with the elements definition) but must
always be 
qualified.

Every element can have one or more foreign schemata introduced to it by
a 
well-known attribute which refers to a schema by URI, and gives it a
short name 
used for qualification.

<XML>
	<*xml-schema xml-ref="http://www.bigbookstore.com/schema"
xml-as="bk" />
	<*xml-schema xml-ref="http://www.w3.org" xml-as="org.w3.www" />
	<bk.ORDERS>
		<*xml-schema xml-ref="http://purl.org/dublincore"
xml-as="dc" />
		<*xml-schema xml-ref="http://www.shipping.com"
xml-as="sh" />
		<LINEITEM XML-ID="LI1">
			<dc.NAME>Number, the Language of
Science</dc.NAME>
			<dc.AUTHOR>Dantzig</dc.AUTHOR>
			<PRICE>5.95</PRICE>
			<sh.ZONE>9</sh.ZONE>
			<*org.w3.www.DSIG>
<*DIGEST>1234567890</DIGEST>

<*SIGNER>AndrewL@microsoft.com</></org.w3.www.DSIG>
			</LINEITEM ></ORDERS></XML>



In the example above, bk.ORDERS comes from the bigbookstore schema. 
Consequently, terms such as lineitem and price, presumably defined in
that 
schema, do not need qualification when used within bk.ORDERS. However,
the terms 
NAME and AUTHOR are drawn from a schema transcending bookstores; they
come from 
the Dublin Core document identified by the URI
"http://purl.org/dublincore". 
Similarly, the DSIG element is defined within the "http://www.w3.org"
schema.

 
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Received on Friday, 16 May 1997 00:14:24 UTC

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