table metadata and the registry

[Douglas Burke]

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

-- 

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   Doug Burke                | Email:  dburke at cfa.harvard.edu
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