RE: [Objectbridge-developers] OJB Homepage, OQL

[<tho...@it...>]

> -----Urspr=FCngliche Nachricht-----
> Von: obj...@li...
> [mailto:obj...@li...]Im Auftrag
> von David W Forslund
> Gesendet: Montag, 22. Januar 2001 20:41
> An: Thomas Mahler
> Cc: objectbridge
> Betreff: Re: [Objectbridge-developers] OJB Homepage, OQL
>
>
> QBE, however, does not deal very well with query filters (like
> inequality, similarity).  There should be explicit support for that
> (which would map directly to an OQL statement).
>
> Dave

You are right of course. I was a bit lazy with my definition of QBE. In f=
act
I am thinking of an "QBE with extensions" that allows composition of quer=
ies
and query filters as in the SODA approach
(http://www.egroups.com/files/oodb/query.html) or in the approach mention=
ed
in the COBRA whitepaper.


>
> Thomas Mahler writes:
>  > Thanks for all your comments regarding OQL and Query by Example (QBE=
)
>  > facilities.
>  >
>  > IMHO it's the best solution to start with a QBE-facility and only af=
ter
>  > that provide an OQL API.
>  > Starting with QBE has 2 advantages:
>  > - It will provide a useful extension to the PersistenceBroker, so th=
at
>  > it can be used even without the ODMG server
>  > - there are some working examples from other projects, that can be
>  > easily adopted to our needs
>  >
>  > Implementing OQL on top of such a facility will work licke follows:
>  > - implement a parser that reads OQL-queries and generates query tree=
s.
>  > - provide a mapping from the abstract query trees to QBE query objec=
ts.
>  >
>  > alternatively one could try to build a parser that directly generate=
s
>  > QBE query objects.
>  >
>  > I will have a look at all the projects you mentioned to find the bes=
t
>  > possible start for the QBE facility. I liked the SODA approach
>  > (www.db4o.com), but I think they are not finished with their spec.
>  >
>  > I'll start with this asap. Right now I'm doing some performance tuni=
ng
>  > deep inside the PersistenceBroker. I'm profiling OJB excution with t=
he
>  > java -Xrunhprof option which gives me some hints about execution hot
>  > spots. I already identified some hot spots in the metadata layer...
>  >
>  > regards,
>  >
>  > Thomas
>  >
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