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Subject: SDO metamodel's weak support for object association

SDO metamodel, unlike UML, does not recognize an object association as
an independent entity and its modeling of the association by Opposite
property of Property is sufficient support but very inefficient. Let say
we have a data object and we want to get all other data objects
associated with it, more precisely, all objects in the data graph
referencing it. Analyzing properties of a data object and its Opposite
property we can find all associations navigable from our data object but
we cannot see associated objects which have reference to our object if
our object does not reference them back (unidirectional association). In
this case we have to go sequentially through the list of all types and
for each one we have to go through its list of properties and to check
if some property references an object of our object's type. If it does
then we have to find all objects of that class and to check each one if
it references our object by current property. The algorithm is complex
and, of course, time and computer resources consuming.

This and couple of other observations are made during development of JPA
DAS, data access service built on top EJB 3.0 persistency manager. JPA
DAS development had to solve a very challenging problem of conversion
and merge of two object graphs implemented in two different
technologies, SDO and EJB 3.0. The algorithms are pretty complex and
they use extensively both metamodels.

Miro Kandic
(408) 525-2596

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