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Part IX: Business Intelligence
■ (^) WMI Data Reader: Executes a Windows Management Instrumentation (WQL)
query against a server to retrieve event log, confi guration, and other management
information.
■ WMI Event Watcher: Similar to a WMI data reader but instead of returning data,
the task waits for a WQL specifi ed event to occur. When the event occurs or the
task times out, the SSIS task events WMIEventWatcherEventOccurred or
WMIEventWatcherEventTimeout can fi re, respectively.
■ XML: Performs operations on XML documents, including comparing two documents
(diff), merging two documents, applying diff output (diffgram) to a document, vali-
dating a document against a DTD, and performing XPath queries or XSLT transfor-
mations. Choose a source document as direct input, a fi le, or a string variable, and
an output as a fi le or a string variable. Set other properties as appropriate for the
selected OperationType.
Deprecated Features
ActiveX tasks and Execute DTS Package tasks were deprecated in SSIS in SQL Server 2012.
Using Control Flow Precedence
Precedence constraints determine the order in which tasks execute. Select any task or
container to expose its precedence constraint arrow, and then drag that arrow to the task
that should follow it, repeating until all items are appropriately related. Any unconstrained
task can be run at the discretion of the runtime engine in an unpredictable and often parallel
ordering. Each constraint defaults to an On Success constraint, which you can adjust by double-
clicking the constraint to reveal the Precedence Constraint Editor, as shown in Figure 52-9.
The upper half of the editor, Constraint options, determines when the constraint should
fi re. It relies on two evaluation operation concepts:
■ Constraint: How the previous item completed — Success, Failure, or Completion
(Completion being any outcome, either success or failure)
■ Expression: The evaluation of the entered expression, which must resolve to either
true or false
These concepts are combined as four separate options — constraint, expression, expression
and constraint, expression or constraint — enabling fl exible constraint construction. For
example, consider a task that processes a previously loaded table of data and counts the
successfully processed rows. The processing task could have two outgoing paths: a success
path indicating that the task was successful and that the processed rowcount matches the
loaded rowcount, and a failure path indicating that either the task failed or the rowcounts
don’t match.
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