Error column in VOResource

[Martin Hill]

Ray Plante wrote:

> On Tue, 18 May 2004, Tony Linde wrote:
> 
>>the registry is a one stop shop for all metadata.
> 
> 
> I disagree with this statement in general.  Besides various pratical 
> reasons of scaling and scope, there is an issue of volitility.  
> 
> Making the registry a one-stop shop for metadata demands a tight coupling 
> with the services they describe.  Any change in the service must be 
> reflected back into the registry.  

Yes - but that's only (reasonably) quick updates and registry 
propogation, rather than tightly coupling form/interfaces.   The form 
coupling is through the VOResource schema, the 'getMetadata' interface 
is simple enough to be loose.

> If the registry is simply about 
> discovering services, the coupling is looser, and the service is more 
> flexible to changes in implementation.  

How do you discover things unless you present data that can be queried? 
  I would have thought that at the least you will want to describe the 
columns of a dataset (if it has columns!), so that any discovery service 
can find the datasets that contain information it wants... Presumably 
you have in mind some other sorts of discovery?

> 
> It can be argued that the tighter the coupling, the more costly the system 
> in terms of software development and coordination of people.  A tightly 
> coupled design may be appropriate for a particular VO project that can 
> manage that coordination; however, it's less appropriate for the IVOA as a 
> whole.  

That's a sweeping statement :-) While I think tools/datacenters should 
be able to present their metadata directly too (but this is how I 
envisaged the registry to harvest the data in the first place), it will 
make the wider VO-level tools even more coupled to the workings of the 
services if they have to go to each one to get its metadata...

> 
> It's an interesting issue that I expect we'll learn more about with 
> experience.

Yes - need to try out some things!

Cheers,

MC

-- 
Martin Hill
www.mchill.net
07901 55 24 66