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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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