Many source-to-target mappings may refer to a flow; in other words, a logical
flow may comprise files coming from several distinct systems. In each sourceto-
target mapping there can reside several types of files, each of them identifiable
with a selection criterion (usually Unix-like selection but also others specific for
the application). These files may need or not need some preprocessing actions like
uncompress, split in smaller chunks, merge, and other application specific action.
Then, these files must be delivered to their destination (another stage of the process).
For each selection at least one termination criterion must be defined; examples of
these criteria may be ???try selection once,??? ???repeat selection until condition,??? or
???other criterion.???
As one can see, this model comprises, in every entity, an escape ???other??? in order
to leave the possibility to insert ad-hoc code when necessary. In our infrastructure,
we used this schematization to build a set of functions to manage file acquisition.
In analogy with synchronization functions, even in this case, we have adopted the
previously described declarative approach.
Loading.Techniques
Every DBMS has its own proprietary techniques for massive loading; here we briefly
treat Oracle, since it is one of the most widespread industrial DBMS. Oracle offers
Figure 5.
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