Mark Woyna wrote:
> usenet@s... (Generic Usenet Account) wrote in message news:<90e5135.0405271429.6c170153@p...>...
> 
>>Does anyone have an opinion on how IDL and WSDL compare to each other?
>> Are they equally powerful in their "expressive power"?  Sometimes it
>>appears to me that IDL is a little easier for humans to follow.  Also,
>>it appears to be more compact.
> 
> How is that possible???!!! I thought XML was selected because it was
> human readable???

Perhaps there's a difference between "compact" and "human readable"? :-)

>>Are IDL and WSDL equally powerful in expressing complex data types,
>>and describing inheritance and association relationships?
> 
> Other than the fact that the Simple Object Access Protocol (SOAP) has
> no concept of Objects, and is in no way simple?

The original question was about WSDL, not SOAP. SOAP is a message
format that has not concept of object, true. (A better comparison
would be between GIOP and SOAP.) But it *is* simple, especially
when you look at GIOP.

Granted, the XML schema language that is used in WSDL for data
type definitions etc. is not that simple. Fortunately, very few
of us have to implement yet another XML parser.

> WSDL has no concept of inheritance or objects. 

True for WSDL 1.1, but WSDL 1.2 has inheritance, cf.
http://www.w3.org/TR/wsdl20/#Interface

> Granted, the overuse
> of fine-grained distributed objects did give CORBA a performance black
> eye in its early days (although no worse than the initial overuse of
> J2EE Entity Beans), it is sometimes necessary to expose a handful of
> stateful objects implementing the same interface in the same server.
> Without the concept of object identity, this is not possible with
> WSDL/SOAP, or at least not trivial.
> 
> Again, accepted practice is to expose singleton "service" objects,
> i.e.
> facade pattern, and keep entity objects behind the facade. Since
> CORBA/IDL can implement either model, many believe that CORBA/IDL is
> more powerful in this respect. On the otherhand, some have argued that
> this capability makes CORBA/IDL  less "simple" that Web
> Services/SOAP/WSDL.

The point for using Web Services is not that you cannot model
services using CORBA, or that Web Services would be capable of doing
everything better than CORBA can. Both statements are just wrong.
This discussion is popping up again and again, as if Web Services
were trying to be CORBA's successor for RPCs...

The point is that Web Services are better suited than CORBA for cross-
domain B2B applications because of a few inherent properties of XML
messaging, frequently summarized as loose coupling. (Extensibility,
finer-grained contracts, marshalling with partial type information,
etc.).

>>What would
>>be the most compelling reasons to choose one over the other?

CORBA delivers better performance, and the type-safe IDL inter-
faces are well-suited for closely integrated intra-domain
applications.

For loosely coupled application-to-application communication
that cannot rely on a homogeneous middleware layer such as
CORBA and may need to be rearranged to integrate more systems
every other month, you will be better off with Web Services.
XML messages are especially suited for document-style inter-
actions, and the performance hit is tolerable in many of
these applications. People also tend to believe that the
firewall-friendliness of HTTP is a good thing...

Regards, Gerald

-- 
Gerald Brose, PhD                       mailto:brose@x...
Xtradyne Technologies                     http://www.xtradyne.com
Schoenhauser Allee 6-7,                  Phone: +49-30-440 306-27
D-10119 Berlin, Germany                  Fax  : +49-30-440 306-78