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From Ole Ersoy <ole.er...@gmail.com>
Subject Re: [DAS to LDAP Type Mapping] Am I thinking about this right?
Date Tue, 03 Apr 2007 23:18:53 GMT
Hey Luciano,

Excellent question, I'm somewhat new to
LDAP myself, but luckily the gang here is
amazingly helpful.  Emmanuel usually answers
before I've had time to press the send button
(I think he has ESPN or something....)
and then everyone else jumps in with lots of helpful
info right after.


Here Goes:
We're trying to minimize mapping
tasks.

There are two ways to do this, which I think you
hinted at in your question.

One is to serialize the DataObject directly
to the LDAP repository (Storing a Java Object in the repository),
but then we loose out on the query capabilities that LDAP offers
us, because the whole object is just a binary blob, and we
would miss the opportunity to make use of the DataGraph's
change summary.

Initially I was thinking the blob way would be good,
just to get going, but I would still break up the
DataGraph into one blob per DataObject.  It turned out
that doing in the LDAP way is much more attractive, and
will most likely perform better (Since we can use the DataGraph).

The LDAP Way:
The other way is to map the simple properties
of the DataObject to preexisting ObjectClasses.

The keyword is "Preexisting".  If we are starting
with a brand new model that has never been written
to the repository, then we need to write the
ObjectClasses that correspond to the model's EClass (In Ecore)
or Type (In the SDO specification) to the repository.

LDAP has the equivalent of Ecore effectively for defining
metadata.

The LDAP Syntax corresonds to the name member of DataType.
The LDAP AttributeType corresponds to a DataType.
The LDAP ObjectClass corresponds to an EClass or Type (SDO)

So the DAS first writes the metadata (Syntaxes, AttributeTypes, and 
ObjectClasses ) to the repository, and then stores each
DataObject instances using this newly defined LDAP metadata.

If we want to map to existing ObjectClasses, then we need
a configuration file, just as with the RDB DAS.

Does that help?

Cheers,
- Ole

P.S. By pure LDAP API, I think you mean JNDI, and yes
JNDI can now be used to query the DataObjects stored
in the LDAP repository, just like
it's used to query the types of
information that is usually
stored in the LDAP repository.




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