Issues relating to simple data and metadata queries

[Doug Tody]

On Tue, 1 May 2007, Patrick Dowler wrote:

> Once you go past that (to metadata about what tables are available
> and how to use them) we have to spec it: which columns have indices,
> which columns have uniqueness constaints, which columns one can/should
> use to join two tables, the cardinality of the join, etc. This is not
> so trivial as it looks; my experience with maybe 3-4 different RDBMSs
> is that they each provide some of the info and other important bits
> are embedded in the data model (cardinality, for example). But you
> have to know these things to write decent queries.
> 
> For the VOResource metadata, I am not familiar with how richly one
> can describe a set of related tables. If someone with that knowledge
> can describe briefly how VOResource can or cannot handle this stuff,
> that would help (me and others, I suspect)... specifically: keys,
> indices (hints), join cardinality, that kind of stuff.

Others could probably address this better than myself, but all I have
been able to find on this is the VODataService schema:

     http://www.ivoa.net/xml/VODataService/VODataService-v1.0.xsd

which defines a DataCollection, which may contain a Catalog, which
is a simple list of Tables with textual description elements added.
A "table" type is {name, description, {columns}+} where a "column"
is a TableParam, the attributes of which are basically just those of
a VOTable FIELD/PARAM.

Thats it - none of the stuff you mention above.  For high level
discovery of course, what the registry provides is probably fine.

 	- Doug