[SCL] Re: The second draft for XML syntax for CL

[Murray Altheim]

[sorry -- sometimes even the most assiduous editing still leaves a
mistake...]

Murray Altheim wrote:
[...]
> These five examples are semantically identical, from the perspective
> of representing a generic SCL quantifier "forall":
> 
>   1.   <forall/>
> 
>   2.   <quantifier type="forall"/>
> 
>   3.   <quantifier>
>          <type>forall</type>
>        </quantifier>
> 
>   4.   <quantifier>
>          <type name="forall"/>
>        </quantifier>
> 
>   5.   <quantifier>
>          <typeRef xlink:href="http://purl.org/xcl/1.0/#forall"/>
>        </quantifier>
> 
> So while the first is very simple, it's impossible to extend the
> XCL syntax without introducing new elements. The second and fourth
> have the advantage of being validate-able using a DTD (using
> enumerated attribute values), the third and fifth could be
> validated using RELAXNG or XML Schema. The second and fourth are
> my choices for what I've called XCL Level 1 and 2.
> Basically, in XCL Level 1 we allow only the <type> element (#3),
> and in XCL Level 2 we allow either a <type> or a <typeRef> (#5).

Actually, I meant to say that the fourth and fifth are my choices.
I'd added some more examples and messed up the numbering. The element
declarations in DTD notation (ignoring for now the rest of the
quantifier's syntax) would be

   Level 1:

      <!ELEMENT quantifier  ( type ) >

   Level 2:

      <!ELEMENT quantifier  ( type | typeRef ) >

Also, when I say things like "the third and fifth could be validated
using RELAXNG or XML Schema", this misses several issues. Any schema
language can be used for all five examples, but certain expressions
can't be constrained, in any schema language. Some types of constraint
are caught at an "application level", i.e., any compliant SCL software.
Not all validation should happen at the syntax level, nor could it.
Validation is a complex issue in its own right.

> Again, remember that from an XML perspective, all five are
> semantically identical -- any perceived differences are people's
> aethetic opinions alone. It's not there in the XML.

Summing up, I could write an XML DTD for each of the five example
approaches, and they'd be semantically identical to each other
from an XML perspective. Now, matching them up *correctly* with the
semantics of SCL is another matter, one for careful discussion and
analysis.

Murray

...........................................................................
Murray Altheim                         http://kmi.open.ac.uk/people/murray/
Knowledge Media Institute
The Open University, Milton Keynes, Bucks, MK7 6AA, UK                    .

   "We can now hypothesise with some confidence that those apparently
    happy, calm Buddhist souls one regularly comes across in places
    such as Dharamsala, India, really are happy," said Professor Owen
    Flanagan, of Duke University in North Carolina. -- BBC News
    http://news.bbc.co.uk/1/hi/health/3047291.stm