[xml-h] link typing

Bob DuCharme bobdc at snee.com
Sun Jan 19 15:01:10 GMT 2003

In the "picking up the thread" thread, Dave Pawson and Simon have listed 
some metadata and potential behavior they'd like to see within the scope of 
what a link can be. With that as a context, I wanted to throw out some 
thoughts about link typing. Let's say that someone who develops a schema is 
planning for a lot of links. Part of his or her schema will be the 
enumeration of a set of link types. What could this be?

For a start, I'd like to forget the XLink idea of a link type 
(http://www.w3.org/TR/xlink/#link-types) that tells you what your specific 
choice of types is ("The value must be one of 'simple', 'extended', 
'locator', 'arc', 'resource', 'title', or 'none'."). The document designer 
should be able to pick types appropriate to the domain, and then use that 
typing information as part of link processing.

Each type could be treated as a profile of link metadata settings so that 
they don't all have to individually set for each link. If I decide that, I 
no longer want all my links of type bibref to bring up individual pop-up 
windows, and that instead they should all bring up information in the same 
"Bibliographic Reference" window, I can change the bibref profile, and past 
and future links that use that profile will have the new behavior.

A type could provide a hook to pre-traversal presentation as an aid to 
navigation. A user who knows that text in blue is a link anchor leading to 
a primary source and text in red is a link anchor leading to commentary on 
a primary source can use the results of the link typing to get to the 
appropriate material more quickly. Or it can indicate a different kind of 
typing more related to presentation: perhaps blue text leads to a single 
document but red text is a multi-ended link that, on one platform, displays 
a menu of those potential traversals.

Should the link type be indicated in an attribute, or be implicit from the 
element used to represent the link? For example,  a "type" attribute in a 
link element like this "<link type='bibref' ID="br1234"/>"  may look 
sensible to some people, while representing an element type the same way 
(e.g. <element type="h1">My Story</element>) looks dumb.

In general, just as an element (or link) ID can serve as a hook for further 
metadata/processing not specified with the element (or link), the naming of 
a type for an element (or link) can serve as a hook for further 
metadata/processing that is essential for scaled-up systems, because it 
allows the specification (and revision!) of  processing for a class of 
links. (And, I think the value of typing in addressing scaling issues 
speaks directly to Simon's concern about link maintainability.)

The big (and vague) question is, if typing lets you specify processing for 
a class of links, how do people want to classify links?

Bob DuCharme          www.snee.com/bob           <bob@
snee.com>  "The elements be kind to thee, and make thy
spirits all of comfort!" Anthony and Cleopatra, III ii
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