table metadata and the registry

[Matthew Graham]

Douglas Burke wrote:
> Ray Plante wrote:
>> Hi Tony,
>>
>> On Tue, 8 May 2007, Tony Linde wrote:
>>> One last query, if the URL only returns the 'extra' metadata, where 
>>> does the core service metadata come from? The registry only? Does 
>>> this mean the service provider has to maintain metadata in two 
>>> locations? Surely one additional benefit of the getWhatever method 
>>> is that a service provider can update their registry record simply 
>>> by changing the VOResource record served up by getWhatever?
>>
>> Let's look at this in two evolutionary stages.  In the near future, 
>> the user still goes to a publishing registry and fills out a form. 
>> Consider...
>>   ...an SIA service:  the user need not enter URL for the table 
>> metadata;
>>        this can be set automatically based on the base URL and the
>>        translater service.
>>   ...a theoretical TAP service:  some near-future standard protocol 
>> could
>>        provide this URL-based access as part of its definition; in this
>>        case the URL is set automatically in the record.  If the standard
>>        does not provide this, it can still be handled like an SIA 
>> through
>>        a translator.
>>   ...a Data Collection:  since there is not an associated service to
>>        provide this information, the publisher can optionally enter this
>>        URL explicitly.  A registry may provide tools for formatting this
>>        information.
>> When the form is submitted, the registry decides whether it wants to 
>> retrieve the table metadata.
>>
>> In the next phase, when VOSI is more widely supported, essentially 
>> the same process happens at service machine when the publisher sets 
>> up the VOResource description getRegistration().  The VOSI standard 
>> provides a straightforward way to recognize service resource 
>> descriptions that support getRegistration() (the VOSI capability 
>> extension).  The publisher provides the VOSI URL to the registry.  
>> The registry retrieves the VOResource description.  At that time the 
>> registry decides whether it wants to retrieve the table metadata.
>>
>> In either case, the registry has access to the table metadata if it 
>> wants it, but if it doesn't want it, it doesn't get it anyway.
>>
>
> Ray,
>
> If I have followed your scheme and have a registry entry for my table 
> and then a separate URL for the metadata then a registry, when it 
> harvests this record, can decide whether to follow the pointer to grab 
> this metadata. If I now decide to update the table metadata - perhaps 
> due to a bug or the metadata has changed - then how do registries 
> interested in the metadata get to know about this change? Should they 
> periodically check the metadata URL and rely on mechanisms like etags 
> to find out if there has been a change? Is there some existing IVOA 
> mechanism I don't know about that can do this (which is quite likely ;-)
>
> Ta,
> Doug
>
Hi Doug,

The VOSI interface provides a lastDateMetadataChanged (or something 
similar) method that can be used to check whether what you have is the 
latest version of the metadata.

    Cheers,

    Matthew