RESTful Web services and DAL

[Doug Tody]

On Tue, 13 Mar 2007, Matthew Graham wrote:

> OpenGIS seems to define both a KVP (key-value pair) and XML version to their 
> services which, of course, translates to web services with SOAP and HTTP 
> bindings. Are you proposing to do the same with DAL?

The idea with DAL has always been that a single service instance
could expose both HTTP and SOAP bindings.  For TAP for example,
the current thinking is that the HTTP binding is mandatory for a
service implementation, and the SOAP binding is optional but may be
required for some advanced capabilities.  The latter statement is still
uncertain, as I don't think we really know yet whether these advanced
capabilities (authentication for example, or VOSpace integration)
will require SOAP, or whether they can be implemented with an HTTP
interface as well.

In any case, it could be desirable to define a SOAP interface, or
at least provide a WSDL, for use by client applications which have
bought into using a SOAP toolkit and "prefer" this type of interface.
It is not clear how important this really is, but we don't want to
rule it out, and it remains part of the design.  The only caveat
is, for something like DAL or the Registry, a client application
is probably almost always better off to use a higher level facility
such as VOClient or ACR rather than mess with lower level protocols
directly, in which case a ready-to-use API is already provided.
Hence the importance of the SOAP binding in the long run is not really
clear at this point.

(Although OpenGIS talks about KVP and XML bindings, I have never yet
actually seen anything but HTTP/KVP, e.g., with WMS).

 	- Doug