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XLink olden days

• To: xml-dev@l...
• Subject: XLink olden days
• From: "Simon St.Laurent" <simonstl@s...>
• Date: Sat, 10 Aug 2002 08:00:13 -0400

There are a few pieces of the old XLink drafts that help explain current
arguments, most of which were (I think) put aside in a mad rush to
namespaces as the solution to all such problems.

Unfortunately, the publicly available requirements and goals for XLink
all appear to be post-namespaces.

from http://www.w3.org/TR/WD-xml-link-970731#sec2.
---------------------------
2. Link Recognition

2.1 Linking Element Recognition

The existence of a link is asserted by a linking element. Linking
elements must be recognized reliably by software in order to provide
appropriate display and behavior. XML linking elements are recognized
based on the use of a designated attribute named XML-LINK. Possible
values are SIMPLE, EXTENDED, LOCATOR, GROUP, and DOCUMENT, signalling in
each case that the element in whose start-tag the attribute appears is
to be treated as an element of the indicated type, as described in this
specification. 

An example of such a link: 

<A XML-LINK="SIMPLE" HREF="http://www.w3.org/">The W3C</A>



2.2 Attribute Remapping

This specification describes many attributes that can be attached to
linking elements to describe various aspects of links. Each is given a
name in this specification. It may be desired to use existing elements
in XML documents as linking elements, but such elements might already
have attributes whose names conflict with those described in this
document. To avoid collisions, user-chosen attributes can be declared as
equivalent to those described in this specification using the
XML-ATTRIBUTES attribute.

This attribute must contain an even number of white-space-separated
names, which are treated as pairs. In each pair, the first name must be
one of those described in this specification: (ROLE, HREF, TITLE, SHOW,
INLINE, CONTENT-ROLE, CONTENT-TITLE, ACTUATE, BEHAVIOR, STEPS). The
second name, when recognized in the document, will be treated as though
it were playing the role assigned to the first. For example, consider a
DTD with the following declaration:

<!ELEMENT TEXT-BOOK ANY>
<!ATTLIST TEXT-BOOK TITLE CDATA                #IMPLIED
                    ROLE  (PRIMARY|SUPPORTING) #IMPLIED>

If it were desired to use this as a simple link, it would be necessary
to remap a couple of attributes, which could be accomplished in the
internal subset: 

<!ATTLIST TEXT-BOOK XML-LINK       CDATA #FIXED "SIMPLE"
                    XML-ATTRIBUTES CDATA #FIXED 
                                         "TITLE XL-TITLE ROLE XL-ROLE">

Then in the document, the following would be recognized as a simple
link: 

<TEXT-BOOK TITLE="Compilers: Principles, Techniques, and Tools"
           ROLE="PRIMARY" XL-TITLE="Primary Textbook for the Course"
           XL-ROLE="ONLINE-PURCHASE"
           HREF="/cgi/auth-search?q="+Aho+Sethi+Ullman"/>



2.3 Operational Issues Concerning Link Recognition

There are two distinct mechanisms that may be used to associate the
XML-LINK and XML-ATTRIBUTES attributes with a linking element. The
simplest is to provide it explicitly. However, this practice is verbose,
and would be not only cumbersome but wasteful of network bandwidth in
the case where there are large numbers of linking elements. Fortunately,
XML's facilities for declaring default attribute values can be used to
address this problem. For example, the following would accomplish the
declaration of the A element as an XML SIMPLE link: 

<!ATTLIST A XML-LINK CDATA #FIXED "SIMPLE">



Such a declaration may be placed in either the external or the internal
subset of the Document Type Declaration. Placing it in both subsets
would be the obvious thing to do for convenient network operation. So
doing, at the time of creation of this specification, would cause the
document to fail to be valid. Note that the successful completion of the
current work on a technical corrigendum to ISO 8879 that is in the
process of international ballot would resolve this problem and allow
this practice in valid documents. However, for interoperability, the
declaration should not be placed in both subsets.

--------------------------------------------------------

See also the slightly revised version of this in:
http://www.w3.org/TR/1998/WD-xlink-19980303#remapping

It disappears completely by:
http://www.w3.org/1999/07/WD-xlink-19990726


-- 
Simon St.Laurent
Ring around the content, a pocket full of brackets
Errors, errors, all fall down!
http://simonstl.com

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