The deliverable
of this transition is not expected to be always a complete and accurate
logical design. The designer/administrator in the logical level should examine,
complement, or change the outcome of this methodology, in order to achieve
the goals.
In the context of finding an automatic transition from one model to the other,
there are several problems that should be addressed. Since the conceptual model
is constructed in a more generic and high-level manner, each conceptual entity
has a mapping to a logical entity. Thus, there is a need for the determination
of these mappings. Moreover, we have stressed that the conceptual model is
not a workflow as it simply identifies the transformations needed in an ETL
process. Therefore, it does not directly specify the execution order of these
24 Simitsis, Vassiliadis, Skiadopoulos, & Sellis
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transformations. On the other hand, the execution order is a very important
property of the logical model. So, there is a necessity for finding a way to
specify the execution order of the transformations in an ETL process during
the transition between the two models.
??? Optimization of ETL workflows: In order to design an efficient, robust, and
evolvable ETL workflow, we have to optimize its execution plan.
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