Inheritance in XML [^*]

[Paul Prescod]

Jon Bosak wrote:
> 
> The people who complain that XML does not have clearly
> defined semantics mean "semantics" the way I do -- as a synonym for
> "meaning".  They are concerned that the meaning of a construction like
> 
>    <PATIENT_NAME>Jones~Jane</PATIENT_NAME>
>
> is not completely clear in the absence of a healthcare industry
> standard like HL7 PID.  What I was saying is that the meaning of such
> a construction taken by itself is not just unclear, it really isn't
> there at all.

Well, here I am off being the theorist again.

Just like you, I use semantics and meaning interchangably also (at least I
think I do). If you've taught an XML course recently, I'll bet you find
yourself saying: "this syntax *means* that..." (e.g. "The start tag means
that an element has begun.")

That's because there are several levels of meaning. You use this example:

    <PATIENT_NAME>Jones~Jane</PATIENT_NAME>

At the XML Spec level the text models an abstraction like this:

OBJECT-TYPE=Element
TYPE-NAME="PATIENT_NAME"
ELEMENT-ATTRIBUTES={}
ELEMENT-CONTENT="Jones~Jane"

At a level above that, (let's say HyTime), it might mean:

OBJECT-TYPE=HyperLink
LINK-TYPE=NameLoc
TARGET-NAME="Jones~Jane"

At a level above that, (let's say HL7) it might mean:

OBJECT-TYPE=Patient Reference
TARGET={ a particular referenced element }

In a particular hospital, it might mean: 

OBJECT-TYPE=Patient Reference
TARGET={ an object representing the database record described by the
referenced element }

I know the XML WG went to a lot of work to try and leave semantics out,
but if we can agree that XML specifies the first level of meaning, then we
agree that XML specifies base-level semantics. As long as we agree on
that, we might as well make those semantics precise in the next iteration,
as SGML will do in its next iteration (after 10 years of trying to get
away without it).
 
 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

"Perpetually obsolescing and thus losing all data and programs every 10
years (the current pattern) is no way to run an information economy or
a civilization." - Stewart Brand, founder of the Whole Earth Catalog
http://www.wired.com/news/news/culture/story/10124.html



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