Database Reference
In-Depth Information
Although both the Control Flow tab and the Data Flow tab look similar, sequence containers are available
only on the Control Flow tab and not on the Data Flow tab. This means you can group control flow tasks only
within them, but it is really not much of a limitation since data flow tasks are by their very nature a way of
grouping SSIS tasks.
Figure 7-14 shows an example of a typical control flow design. You will note that similar tasks are grouped
together to form a set of those actions, such as preparing the data warehouse tables to be filled. Other sequence
containers may have different actions, such as filling up dimension tables or filling up fact tables.
Figure 7-14. Grouping control flow tasks with the sequence container
In cases where you are using the ush-and-ll technique to fill up your data warehouse tables, you need a
task that clears the tables before they are refilled. In Chapter 6, we discussed using the SQL truncate command
for this process. You must drop the foreign key constraints before you begin truncation. This is accomplished by
adding the code that you created in Chapter 6 to an Execute SQL task.
While the code to drop the foreign key constraints and the code to truncate the tables could be placed in
one control flow task, it provides a better visual to create two tasks—one to drop the foreign key constraints and
one to do the truncation. Since both of these tasks are part of a single process, it is logical to group them. In SSIS,
a sequence container is specifically designed for this job. In Figure 7-14 you can see that we have created two
Execute SQL Task items and placed them inside a sequence container called Prepare ETL Process Sequence
Container.
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