I think we are talking about the same thing but different terminology (expecially me).
I am new to REST but I'll try to explain what my intentions are:

In REST, each resource has a URL which uniquely identifies the resource. Here, I'd like to have a URL that identifies a molecule/descriptor, and by calling it with HTTP GET it will return the actual molecule/descriptor. So when I say REST ID I should probably say Resource URL. Maybe even, in the xml, use URL instead of ID?

On Jan 7, 2008, at 16:12 , Rajarshi Guha wrote:

What do you mean by this? I have provided a web service to get  
descriptor specifications and REST URL to the desc specs for all  
descriptors is

http://rguha.ath.cx/~rguha/cicc/desc/descriptors/specifications

Does this work for you?

Yes, this is good. Do individual descriptorSpecifications also have URL's? Like: 

http://rguha.ath.cx/~rguha/cicc/desc/descriptors/specifications/org.openscience.cdk.qsar.descriptors.molecular.ALOGPDescriptor

will return:

<DescriptorSpecification class="org.openscience.cdk.qsar.descriptors.molecular.ALOGPDescriptor">
<SpecificationReference>
http://www.blueobelisk.org/ontologies/chemoinformatics-algorithms/#ALOGP
</SpecificationReference>
<ImplementationTitle>
org.openscience.cdk.qsar.descriptors.molecular.ALOGPDescriptor
</ImplementationTitle>
<ImplementationIdentifier>$Id: ALOGP-MR descriptor  $</ImplementationIdentifier>
<ImplementationVendor>The Chemistry Development Kit</ImplementationVendor>
</DescriptorSpecification>

And:
http://www.blueobelisk.org/ontologies/chemoinformatics-algorithms/#ALOGP
would be the URL of the descriptor.
Egon: This URL does not work. It should return the XML description for this descriptor, right?