An STC "when" and "where" example

[Matthew J. Graham]

Hi,

>> Any parser that feels like it (or knows what they say) can skip the 
>> included documents which are going to be part of a standard IVOA 
>> library.
>
> Sorry, I have to take issue with this...
>
> Are you going to sit down and write factory and parser toolkits in 
> Perl, Python, Ruby, C, C++, C#, Fortran, Java, PHP and the half dozen 
> other languages currently in use inside various projects that will be 
> involved in creating and parsing VOEvent messages?

OK, let's be realistic here: if you are serializing XML across the Web, 
I believe with 95% confidence that you are using Java, C#, Perl or 
Python (does anyone really write pure Fortran web services?) so we need 
STC support libraries in these four languages. Now Java has binding 
toolkits to handle XML <---> Java object and it needs to verified that 
these will work with the STC schemata (previous versions have not). I 
suspect that C# has a similar toolkit and Perl/Python?

Of course, the alternative way to access these verbose XML documents is 
to apply an XPath statement against the XML document to retrieve the 
elements/attributes you want:
if I had Java bindings for Arnold's example then I would call some 
getValue2() method to access the RA,Dec pair but in the XPath example, 
I would do: //crd:Position2D[crd:Name = "RA,Dec"]/crd:Value2. Now I 
know that Java, Perl and Python all have XML libraries that let you do 
this sort of thing on an XML document and the XPath statements will be 
the same in all cases so we should certainly think about XPath 
accessors as a way to do easy parsing.

The harder part is actually creating the documents. With standards like 
XForms being increasingly supported, doing this through an interactive 
form on a browser is straightforward - some of the registries already 
do this based on the VOResource schemata which are just as complex. 
This just leaves programmatically creating the document: binding is 
good here where it is possible, otherwise a simple solution might be 
stylesheets that would populate an XML STC document from a simpler 
key-value pair document: default values could also be defined in the 
stylesheets.

This type of approach will actually work with most of the languages you 
mention with little additional work once it is implemented.

	Cheers,

	Matthew