Problems about the Spectrum Data Model from the view of a Web Service programmer

[Doug Tody]

Hi Laszlo -

On Thu, 14 Sep 2006, Dobos, Laszlo wrote:
> I just ran through the document quickly, because I was interested in the Web
> Service issues. I'm pretty sure that from the scientific view the data model
> is very well designed, and your work on collection and organizing the
> enourmous number of different metadata fields is appreciated, but I've found
> some problems that may cause trouble in a web service aware application.

These look like very good pointers about how to serialize using XML
in a SOAP context, which will come up in some applications.  My main
comment about the Spectrum DM though, is that for an object of this
complexity (also for VOTable, FITS, etc.) we would want to use a
document-oriented interface.  That is, rather than expose a Spectrum
serialization directly in SOAP, we would pass the XML version of
Spectrum as a string or other blob, much as we would for the other
document formats such as VOTable or FITS.  A SOAP interface to SSA
could use conventional SOAP encoding for the query input parameters,
but the query response or spectrum object would be passed back as a
blob (or maybe just directly as a MIME-type identified response).

Hence it is not clear that compatibility of a complex model such
as Spectrum with SOAP is an issue.  The biggest difference between
the JHU spectrum services and the DAL approach is probably this
document-centric versus SOAP/RPC approach.  The document-centric
approach is admittedly more complex, but is required to support
multiple data formats (including non-XML ones), and has other
advantages such as separating the object code from the specific
interface or protocol used.

 	- Doug