Remarkably, in most projects the DFM was
also used to directly support dialogue with end users aimed at validating requirements,
and to express the expected workload for the DW to be used for logical and
physical design. This was made possible by the adoption of a CASE tool named
WAND (warehouse integrated designer), entirely developed at the University of
Bologna, that assists the designer in structuring a DW. WAND carries out data-driven
conceptual design in a semiautomatic fashion starting from the logical scheme of
the source database (see Figure 8), allows for a core workload to be defined on the
conceptual scheme, and carries out workload-based logical design to produce an
optimized relational scheme for the DW (Golfarelli & Rizzi, 2001).
Overall, our on-the-field experience confirmed that adopting conceptual modeling
within a DW project brings great advantages since:
??? Conceptual schemata are the best support for discussing, verifying, and refining
user specifications since they achieve the optimal trade-off between expressivity
and clarity. Star schemata could hardly be used to this purpose.
??? For the same reason, conceptual schemata are an irreplaceable component of
the documentation for the DW project.
??? They provide a solid and platform-independent foundation for logical and
physical design.
??? They are an effective support for maintaining and extending the DW.
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