Completeness of SkyNode entries in registry

[Tony Linde]

There has been an offline debate carried on over the past week between a few
people in NVO and AstroGrid about how to handle incomplete registry entries
for SkyNode services.

Basically, a SkyNode service will register as a TabularSkyService type of
resource: this is a SkyService with additional table/column/ucd information
included. However, this additional information is optional and the NVO
project have decided that such information should be provided by the data
service (in SkyNode via two separate methods: Tables and Columns) instead of
in the registry entry. The AstroGrid project believes this essential
information ought to be part of the registry entry as specified.

This difference of opinion will mean that registries constructed under the
two projects will differ in approach and that application writers will need
to be aware of these differences. Put simply, the AstroGrid project registry
will 'fill in' any SkyNode entries which are incomplete by getting the extra
information from the service (method outlined below). So a registry entry
for SkyNode service retrieved from an AstroGrid-type registry will have the
tables/columns/ucd information. Entries retrieved from NVO-type registries
may not have this information.

What this means is that application writers who do not want to code the need
to look up the extra metadata information from every service they wish to
use should mandate that, when they are installed, they should be connected
(presumably via a config file entry or similar) to an AstroGrid-type
registry. Those applications which do not want to mandate this will need to
cater for handling incomplete registry entries, ie will need to retrieve
such metadata from the services themselves.

AstroGrid will endeavour to do the same for any future services where
essential metadata for the service is only optional in the registry and
provided via a separate mechanism. We will attempt to make the registry a
one-stop shop for all metadata to save application writers from unnecessary
effort (in ongoing maintenance as well as in development).

Cheers,
Tony. 
=======

The method AstroGrid will use (still under debate) to 'complete' SkyNode
entries is:

A. AstroGrid registry will harvest from other registries. After a harvest,
it checks for any SkyNode entries (we'll later need some way of making this
expandable to other standard interfaces which may not be supported
completely) and, if they are incomplete, calls the service to retrieve the
extra metadata.

B. With the extra metadata, the registry constructs a complete
TabularSkyService entry with the *original* identifier, changes the
identifier of the old entry to old://__whatever__, adds the complete entry
and the old entry (deleting any existing matching old:// entry).

C. On a periodic basis, a separate registry process will scan all the old://
entries and poll the matching services to check if any of the extra metadata
has changed; if it has, the original entry is updated.

__
Tony Linde                 
Phone:  +44 (0)116 223 1292    Mobile: +44 (0)7753 603356
Fax:    +44 (0)116 252 3311    Email:  ael at star.le.ac.uk
Post:   Department of Physics & Astronomy,
        University of Leicester
        Leicester, UK   LE1 7RH

Project Manager,            Director,
AstroGrid                   Leicester e-Science Centre
http://www.astrogrid.org    http://www.e-science.le.ac.uk/