![](bg8.png)
end of the complex object operation, i.e., within
commit() of the current, nested transaction.
5 CONCLUSION
In this paper, we have proposed adding ORN to the
ODMG Object Model and have referenced, illus-
trated, and discussed algorithms for implementing
ORN semantics in an ODMS. The shortcomings of
our proposal are that the Object Model is made
slightly more complex and ODMS implementations
must include a nested transaction capability. Despite
these shortcomings and regardless of whether or not
ORN is added to the ODMG standard, we believe
that vendors should strongly consider including
ORN as an extended feature to their ODMSs. We
conclude by summarizing the reasons:
• ORN is a simple notation that allows the data-
base developer to specify a variety of association
semantics, which define the scopes of complex
and composite objects.
• The extended ODL would facilitate a straight-
forward mapping of association semantics from a
conceptual database model, expressed as an
ORN-extended UML class diagram, to the logi-
cal database model, expressed in the ODL.
• The ODMS would provide the same support for
associations that is provided by relational
DBMSs via the
SQL references clause plus sup-
port even more powerful association semantics.
• If no
<association> is given for a traversal path,
the default
<association> corresponds to current
system capabilities. Thus, adding ORN is a pure
extension requiring no changes to the underlying
Object Model capabilities.
• The implementation of this extension is rela-
tively simple as shown by the algorithms we
have made available and their implementation in
OR+.
• The benefits are increased database development
productivity and improved database integrity as
much less code needs to be developed and main-
tained by database application developers.
ACKNOWLEDGEMENTS
This work was partially supported by the NSF co-
operative agreement HRD-9707076.
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