Applications have an increasing need to manage semistructured
data (such as data encoded in XML) along with conventional
structured data.  We extend the structured object database model
ODMG and its query language OQL with the ability to
handle semistructured data based on the OEM model and Lorel language,
and we implement our extensions in a system called Ozone.
In our approach, structured data may contain entry points to
semistructured data, and vice-versa. The unified representation and
querying of such ``hybrid'' data is the main contribution of our work.
We retain strong typing and access to all properties of structured portions of
the data while allowing flexible navigation of semistructured data
without requiring full knowledge of structure. Ozone also enhances both
ODMG/OQL and OEM/Lorel by virtue of their combination.  For instance,
Ozone allows OEM semantics to be applied to ODMG data,  thus supporting
semistructured-style navigation of structured data. Ozone also enables ODMG
views of OEM data, allowing standard ODMG applications to access
semistructured data without losing the benefits of structure.
Ozone is implemented on top of the ODMG-compliant O2
database system, and it fully supports our extensions to the ODMG
model and OQL.