[DAS] Relationship info using DBMS Metadata getCrossReference() - pros and cons?

[Amita Vadhavkar <am...@gmail.com>]

(Prev mail thread:-
http://www.mail-archive.com/tuscany-dev@ws.apache.org/msg20770.html)
More on this...
Looks like, single table registry approach was taken to dump all rows
fetcted from database
without linking DataObjects, as there is no relationship information in DAS
Config.
So, from the above mail thread, as join between singer and song returns 3
rows, there were
3 singer DOs and 3 song DOs and it is user's responsibility to see that out
of 3 singer DOs
2 are actually identical.

So question here is...can DAS use DatabaseMetadata.getCrossReference() JDBC
API to form
relationship information when it is missing in DAS Config. To keep matter
simple, DAS can
take approach of using DAS Config relationship info as first priority and
DatabaseMetadata.getCrossReference()
 as next priority. In case queries involve tables where for some
relationship is defined in DAS Config and for some
it is not, DAS can just stick to DAS Config. i.e. avoid mixing DAS Config
provided relationship info and DBMS provided
relationship info. Whatever is the approach (we can take mixed approach too,
for that matter), it just needs to be
documented clearly.

DAS - from the basic usage so far, promotes less config and thus uses DBMS
Metadata info for tables
and columns when one is not available in DAS Config. So same can be extended
for Relationships too.

Are there any known issues around usage of
DatabaseMetadata.getCrossReference()?
Checked for Derby, MySQL so far and found no issues. Also, if some vendor do
not have
implementation for this method, we can detect exception/null/empty ResultSet
returns and
continue the way we are at present using SingleTableRegistry.

Comments?

Regards,
Amita