1175
Chapter 52: Building, Deploying, and Managing ETL Workfl ows in Integration Services
52
FIGURE 52-9
The Precedence Constraint Editor.The lower half of the editor, labeled Multiple constraints, determines how the downstream
tasks should deal with multiple incoming arrows. If logical AND is chosen (the default),
then all the incoming constraints must fi re before the task can execute. If logical OR is
chosen, then any incoming constraint fi ring causes the task to execute. Logical AND is
the most frequently used behavior, but logical OR is useful for work fl ows that split apart
and then rejoin. For example, control can split when an upstream task has both success
and failure branches, but the failure branch needs to rejoin the normal processing after
the error has been resolved. Using a logical AND at the merge point would require both the
success and the failure branches to execute before the next task could run, which cannot
happen by defi nition. Logical AND constraints are presented visually as solid lines, whereas
logical OR constraints are dotted lines.The arrows that represent precedence constraints provide other visual clues as to the type
of constraint. Green arrows denote a success constraint, red a failure constraint, and blue
a completion constraint. Constraints that use an expression include an f(x) icon. There is
no visual queue to distinguish between a Constraint AND expression versus a Constraint
OR expression, so it is best to double-check the Precedence Constraint Editor when an f(x)
displays. For example, a green arrow with an f(x) displayed could fi re even if the preceding
task had failed, given that the expression had been satisfi ed and the Constraint OR expres-
sion option was chosen.Using Data Flow Components
This section describes the individual components that you can confi gure within a Data Flow
task: sources of data for the fl ow, destinations that output the data, and optional transfor-
mations that can change the data in between.c52.indd 1175c52.indd 1175 7/31/2012 10:29:28 AM7/31/2012 10:29:28 AM
http://www.it-ebooks.info