getCapabilities() and graininess

[Ray Plante]

Tony,

On Thu, 10 May 2007, Tony Linde wrote:
> This could be a problem for registries which do store the table/column
> metadata: they're not going to want to hit all the services so registered if
> the registry already contains the information. So we'd need a separate way
> of harvesting full information - yes?

I don't follow.  Are you saying that an original resource record has both 
the URL and the table metadata explicitly included?  You will have an 
obligation to emit the original record through your harvesting interface; 
however, it is your choice what you index for searching.  Is this what you 
mean?

> Also, how does a service/registry indicate that it has updated the
> table/column metadata? Do we say that the current mechanism applies to all
> metadata, whether the home registry holds detailed metadata or not?

Think of the table metadata as being external information that some 
registries choose to collect and incorporate into their search
capabilities.  Thus, when Registry B asks for records that have been 
updated since=suchandsuch, this would *not* include changes to the table 
metadata, unless that metadata were explicitly listed in the original 
record.

As for Registry A that wants to retrieve the table metadata from the 
service and keep it up to date, it can check, if it wishes, the 
last-Modified HTTP field for the URL (as described in the VOSI for 
getRegistration()).  Or perhaps it's content to just replace the file 
everytime it visits the resource.

>>        want AstroGrid users to use NVO resources in the query builder, we
>>        have to provide table metadata from our registries.
>
> No, I thought we'd agreed that if the home registry does not keep the fine
> metadata, it is up to the harvesting registry to get it from the service.

Is that what is actually happening?  Then can you do that for all your 
resources?  Either way, a standard table description format available from 
a URL recorded in the resource record would help that as you would have 
a common way of getting the info, regardless of the type of service.

cheers,
Ray