Minutes MWG 2003-09-25

[Tony Linde]

Hi Alberto,

> A registry could very well be implemented using a relational database.

No-one has said that it couldn't.

> To answer to Tony:
> In SQL this will be somthing similar:
> 
> select a.resource_id, a.resource_title, a.resource_date
> from   Resources a, Resources_Curators b
> where a.resource_id = b.resource_id
>   and b.creator = "Messier"
> 
> 
> I do not see your point, sorry Roy.

The point is that this only works if you have a table called Resources and
another called Resources_Curators. Our goal was *not* to mandate the way a
registry operated or was structured, only the core metadata and the way that
different registries interoperated.

Cheers,
Tony. 

> -----Original Message-----
> From: owner-metadata at us-vo.org 
> [mailto:owner-metadata at us-vo.org] On Behalf Of amicol at eso.org
> Sent: 03 October 2003 00:37
> To: Roy Williams
> Cc: Ray Plante; metadata at us-vo.org; registry at ivoa.net
> Subject: Re: Minutes MWG 2003-09-25
> 
> 
> 
> Just a word (or two) in defence of relational databases.
> 
> Quoting Roy Williams <roy at cacr.caltech.edu>:
> 
> > (1) ADQL is semantically similar to SQL, it is something 
> for querying 
> > relational databases like star catalogs
> 
> A star catalog is not a relational database.
> A star catalog could be expressed as a relation within a 
> relational database. 
> or as a XML document, eg a VOTable.
> 
> > 
> > (2) Xquery is for querying hierarchical databases (like XML 
> > documents). (see
> > example* below). Xquery is made for XML (which VOResource 
> is), and there are
> > existing implementations.
> > 
> > I believe that we are agreed that an SQL-type language is best for 
> > relational databases of stars,
> 
> SQL is a very good language for relational databases 
> Relationalships in such databases can be quite complex, 
> not just a star catalog.
> 
> > and that our agreement from Cambridge covers
> > this. However, the registry is different from a star catalog in 
> > several ways
> > (a) the structure is more complex, with repeated elements 
> (eg authors), and
> 
> Repeated elements are obviously not handled in a relational 
> database within a single table; furthermore N to M 
> relationships can be handled in a relational database by 
> adding so called junction tables.  
> A registry could very well be implemented using a relational database.
> 
> > (b) the amount of data is much less. In other words, the 
> registry is 
> > *metadata*, not *data*.
> 
> Databases are a very natural place for storing metadata.
> At least this is what I have been doing in my last ten years 
> ... And SQL is out there since the seventies.
> 
> > There is not much experience on querying these --
> > because we do not actually have any significant VO registries yet!
> > 
> > Querying the registry is not a solved problem (like SQL and star 
> > catalogs). There is no benefit in entrenching ourselves in 
> a position. 
> > I think we in the IVOA should continue to investigate ways to make 
> > client software for VO registries, and hope that by this time next 
> > year we will be sufficiently informed to consider a 
> standards process.
> > 
> > Roy
> > 
> > --------------------------------
> > * Xquery example (approx) -- would select the Messier 
> catalog from the 
> > resources in the Caltech registry:
> > 
> > <query>
> > { for $b in document("nvo.caltech.edu/registry.xml")/VOResource
> >   where $b/Curation/Creator="Messier" and $b/@date<1800
> >   return <resource year="{$b/@date}"> {$b/Curation/Title} 
> </resource> 
> > } </query>
> > 
> 
> To answer to Tony:
> In SQL this will be somthing similar:
> 
> select a.resource_id, a.resource_title, a.resource_date
> from   Resources a, Resources_Curators b
> where a.resource_id = b.resource_id
>   and b.creator = "Messier"
> 
> 
> I do not see your point, sorry Roy.
> 
> I do not want people to confuse the concept described in a 
> schema (like the SRM) with the way the schema is implemented. 
> I only need a good schema. After that, nobody would stop me to create 
> my own copy of the registry using the technology I prefer, if 
> I so like, 
> provided that I comply to the defined and agreed upon 
> standards for its interfaces.
> 
> Alberto
>