proposed VODataService changes

[Patrick Dowler]

On 2008-5-21 05:43, Francois Ochsenbein wrote:
> Do you mean it would be legal that a <join> in the Registry can define
> a foreign key which would refer to a column of a table of another catalog
> -- in other terms, a foreign key to another data server ?

No, I meant catalog in the sense used in ADQL/SQL (eg often called database 
within a server). It is generally permitted to join across catalogs. My 
understanding is that there is a CatalogService element that corresponds to 
the whole service (eg db server).

Note that the distinction is important because if a particular server uses 
catalog and table (and implicit schema), you still need two dots between the 
catalog name and the table name. This is a relatively common way to use a 
database. On the other hand, if you use the default database and require a 
schema, there is one dot between the schema and table names. So, if these 
table name qualifiers are needed for particular server, the metadata needs to 
distinguish between them or otherwise (somehow) make sure the user gets the 
right number of dots.

PS-Of course, this is assuming a service implementor wants to be able to pass 
through the fully qualified table names that the user put in the ADQL. If the 
service is willing or required to parse the ADQL and modify the table names, 
then they can just never expose catalog and schema names (just make sure 
table names are unique and map them internally).


-- 

Patrick Dowler
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