Hi Tony,
One thing to keep in mind about ADQL is that while it has a data model--that is, it has the same basic components--as SQL (XQuery has similar components), it is rendered in XML with its contraints parsed into a tree. A main objection to using either SQL or XQuery is that implementers would invariably find themselves having to parse the queries to transform them into a form that can be used by the local database. XML, of course, is easier to parse and transform.
This has numerous advantages, including:
Mapping XML into a relational model is always a challenge, of course, and we in the NVO have been exploring various techniques. In my current favorite scheme, column names are simple XPaths.
On Thu, 2 Oct 2003, Tony Linde wrote:
> Given schema 0.8.2/3, what would a SQL-like query look like?
With many details glossed over...Where one puts a column name an XPath to the Resource metadata element would go.
While I don't think we can say for sure that ADQL is the right answer at
this time, I don't see a compelling reason yet to say that registries
should be treated differently from other databases. (We still
need to compare coverage regions and such in both cases.)
Nevertheless, prototyping different search languages is a good idea at
this time. We may discover the fundemental differences or different
requirements. Or we may discover requirements that need to be placed on
ADQL.
cheers,
Ray
Received on 2003-10-03Z00:38:00