Best Practice for adding a "standard data item" to pre-existing XML voca

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

I am interested in your thoughts on this issue.  Please see the
questions interspersed below.  /Roger

ISSUE

Suppose that a number of different communities have already created
their own unique XML vocabularies.  To promote cross-community
interoperability (including mashups) the communities decide to
standardize "When" information since they all have, in one form or
another, "When" information.  What is best practice for incorporating a
standard information item (e.g. a "When" information item) into a
diverse set of pre-existing XML vocabularies?

EXAMPLE

Suppose there are three communities:

1. The Office Supplies Community

2. The Airline Community

3. The Book Community

Here are three XML documents which illustrate the XML vocabularies that
each community already has created:


SAMPLE XML DOCUMENT FOR THE OFFICE SUPPLIES COMMUNITY

<Memo>
   Hi Folks,
   Let's meet in <time>one hour</time> to
   discuss our strategy for the way ahead.
</Memo>


SAMPLE XML DOCUMENT FOR THE AIRLINE COMMUNITY

<Flight>
    <takeoff-time>Saturday, March 14, 4:30 PM EST</takeoff-time>
    <arrival-time>Sunday, March 15, 6:00 PM (local time)</arrival-time>
</Flight>


SAMPLE XML DOCUMENT FOR THE BOOK COMMUNITY

<Book>
    <publication-date>
        <month>January</month>
        <year>2005</year>
    </publication-date>
</Book>


EVERY COMMUNITY USES "WHEN" SO LET'S STANDARDIZE THAT!

All three communities express "When" information, albeit in unique
ways:

Office Community:

<time>one hour</time>

Airline Community:

<takeoff-time>Saturday, March 14, 4:30 PM EST</takeoff-time>
<arrival-time>Sunday, March 15, 6:00 PM (local time)</arrival-time>

Book Community:

<publication-date>
    <month>January</month>
    <year>2005</year>
</publication-date>

It is decided to use ISO-8601 as the standard.

What approach should be used to add the standard datetime information? 


DESIRED FEATURES OF A SOLUTION

1. Basic interoperability: standardizing just the "When" data obviously
will not magically enable, for example, the Airlines' applications to
be able to process all the data in an XML document from the Book
community. It will, however, provide one common piece of understanding.
Thus, for example, an Airline application could pull out the "When"
data from a document it receives from the Book community and do a
mashup of it with its timeline application.

2. Progressive Enhancement (Scalable): today the communities
standardize on ISO-8601 but in the future they may want to use other
standards as well, such as the vCard dtstart and dtend (datetime-start
and datetime-end). 

3. Graceful Degradation: suppose some of the Airlines' applications
upgrade to be able to process the new "When" standard while others
don't.  Suppose an application that has not been upgraded to understand
the new "When" standard receives a document that uses it.  The
application must be able to safely ignore it and gracefully degrade to
the basic Airline markup.

4. Minimally Disruptive: each community already has a significant
investment in their XML vocabularies (including applications designed
to manipulate those vocabularies).  So, a solution must be minimally
disruptive for it to be cost-effective.

QUESTION: what other desired features that should be listed here?


EXEMPLARS (EXISTING COW PATHS)

There are a number of technologies that address similar problems, and
exhibit the desired features listed above:

1. XLink
2. RDFa
3. Microformats
4. Nonintrusive CSS
5. Nonintrusive JavaScript

The first three work by providing attributes that can be injected
anywhere into an existing XML vocabulary.

The later two work by placing the enhancements into separate documents.


SOLUTION #1

Create an attribute of type ISO-8601:

<schema targetNamespace="http://www.example.com/standard/when";
       
    <attribute name="when" type="datetime" />

</schema>

Here's how the three communities utilize this solution:


SAMPLE XML DOCUMENT FOR THE OFFICE SUPPLIES COMMUNITY (ENHANCED)

<Memo xmlns:common="http://www.example.com/standard/when";>
   Hi Folks,
   Let's meet in <time common:when="2008-03-28T13:30:00">one
hour</time> to
   discuss our strategy for the way ahead.
</Memo>


SAMPLE XML DOCUMENT FOR THE AIRLINE COMMUNITY (ENHANCED)

<Flight>
    <takeoff-time common:when="2008-03-14T16:30:00">Saturday, March 14,
4:30 PM EST</takeoff-time>
    <arrival-time common:when="2008-03-15T18:00:00">Sunday, March 15,
6:00 PM (local time)</arrival-time>
</Flight>


SAMPLE XML DOCUMENT FOR THE BOOK COMMUNITY (ENHANCED)

<Book>
    <publication-date common:when="2005-01-01T00:00:00">
        <month>January</month>
        <year>2005</year>
    </publication-date>
</Book>

Each community adds the standard "common:when" attribute to whatever
element makes sense for their XML vocabulary.

An application that has been upgraded to understand the new standard
can simply extract the "common:when" attribute value.


SOLUTION #2

Solution #1 is slightly disruptive - each community will need to modify
their schemas and instance documents to account for the new attribute.
However, solution #1 does exhibit all of the other desired features
listed above.  

Solution #2 is: put the standard "When" information into a completely
separate document (analogous to how CSS can be put into a completely
separate document, and yet it still gets integrated with the markup by
the browser).

I am stuck.  I do not know how to implement this second solution.  How
would, say, the Book community markup this data  2005-01-01T00:00:00,
put it into a separate document, and then connect the markup to the
<publication-date> element in the other document?  Any exemplars
(existing cow paths) for this second solution? 

Thanks!  

/Roger