is prohibited.
expressions to describe paths on the graph. In this context, the problems are
related to the definition of a simple and intuitive syntax allowing the user to
express complex temporal clauses, and to the definition of a query language
which is general and flexible enough to overcome difficulties coming from
the semistructured nature of data.
??? Data aggregation and materialization: In the semistructured data context
the same information can be structured in different ways, thus an interesting
point is the study of suitable techniques to aggregate data having different
structure, choosing a common graphical representation. Moreover, the result
of data aggregation can be seen as a view on the data warehouse, and thus it
could be interesting to materialize the view itself, and to study different possibilities
to store data in the view, and to relate them to the original information.
??? Representation.of.versions: In the XML data warehouse context, it could
be useful to maintain the successive versions of an XML document stored in
the data warehouse. A graphical representation of versions could be studied
and proposed. The graph-based approach for representing successive versions
would represent the valid time of data, and the valid (transaction) time of the
document version. In this case the problem to consider is related to the best
representation of different versions of the same document.
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