ImageDM: what does extension mean?

[Mireille Louys]

Dear Ray , Dear all,


On 25/10/2013 18:57, Ray Plante wrote:
> Hi DMers,
>
> If you were at the IVOA Interop meeting, then you know that image cube
> access was a big topic, and the ImageDM is one of the key standards
> targetted to support it.  We also resolved to get greater
> participation in and discussion of these specs going forward, and I
> was hoping I might inspire a bit of that with a question about
> ImageDM.
>
> At the Interop, there was a resolution to make the ImageDM be an
> extension of ObsCore.  The purpose of this is to provide greater
> interoperability SIAv2 and ObsTAP:  that is, you might discover data
> cubes with either one, and you're query results would be based on a
> common data model.
>
> My question is, what does it mean technically for ImageDM to "extend"
> ObsCore?

>
> One result we might expect is that the ImageDM would not be explicitly
> "re-defining" the ObsCore metadata and UTypes; rather it would point
> to the ObsCore document for its definition.

> Is there more to it,
> though?  Is there something implied about the structure of UML models?
The work is to be done at the level of the definition of the classes: 
the core Classes already defined in ObsCore , the particular classes 
necessary to cover Image and cubes descriptions.
The design work and definition is at the level of classes and UML .
VOdml and Utype strings , old style or new style are only derivations of 
this logical human brain elaboration.

 From my point of view we need : UML graphs (as started by Mark) and 
description text to clarify the goal, scope and details of the classes.
from this we can derive :
- the VO-DML representation of these models providing an XML document 
encoding the models
- a utype list derived from this XML representation

The argument a la "ancients against moderns" about utype syntax should 
not prevent us to do good job in object oriented design , that is at the 
UML level.
Note that from a VO-DML data model file : PhotDM.xsd , or another DM, 
VO-urp the precursor of VO-DML , used to extract full xpath Utypes.

Let's resolve the classes re-use first and then adjust the Utypes syntax 
with the benefits of the two approaches in a second run.

Cheers , Mireille

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Mireille LOUYS          mailto: mireille.louys at unistra.fr
                                       
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