Above all, we must consider the problems in accessing data owned by other departments,
groups, and so on; obtaining the necessary grants to access data is not
always easy for both technical and nontechnical reasons. These political problems
0 Adzic, Fiore, & Sisto
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can impose constraints and work-around that make the ETL process more complex.
Another topic is the absence of internal enterprise standardization. It can be very
difficult to find the same rules (even in the same department) in naming files, in
expressing a date, in choosing a structure for files, and so forth. These problems,
involve very general questions like standardization, metadata, and so forth, and
cover a relevant part in the ETL process design.
Requirements,.Constraints,.and.Criticalities
In a DW project (as in every project), the most important step is the requirements
collection. A well-defined set of requirements is essential in order to individuate
the best approach to ETL. If the DW must be loaded once a week, with limited
transformation complexity and volumes, then one can choose any preferred approach
and hence skip this chapter entirely. In this case, ETL means loading data
into DBMS with simple transformation; a normal knowledge of SQL and expertise
in programming/scripting is enough to achieve the objective in many cases.
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