Design and implement ETL control flow elements, including containers, tasks, and precedence constraints

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Control Flow

It is called “control flow” because this is where you design the sequence of steps in your package and direct how they flow from one to the next.

There are four main types of items and objects in the Control Flow tab.
  • Control Flow Tasks
  • Precedence Constraints
  • Containers
  • Connection Managers
The most commonly used Control Flow tasks are grouped under the Common section in the SSIS Toolbox window. This task can be done against the Filesystem level, Database level, Analysis Services level, Package level, Hadoop level, etc. to consume, transform, and load data.

Precedence Constraints
You can control the sequence of tasks that get executed based on completion, success, or failure of a task.
  • On Success (Green arrow) Proceeds to the next step only if the current step completes with Success. 
  • On Completion (Black arrow) Proceeds to the next step regardless if current step completes with a Success or Failure.
  • On Failure (Red arrow) Proceeds to the next step only if the current step Fails. 
There is an additional layer of condition that can be applied to the precedence constraints by using Expressions, and expressions can be combined with Success/Failure/Completion requirements.

Containers 
Containers are used for organizing and grouping units of work that run together. There are three types of containers:
  • For Loop Container Used to loop through and run everything inside the container a fixed number of times
  • ForEach Loop Container Used to loop through and run for each item (e.g. all the files in a folder that need to be archived)
  • Sequence Container Used only for grouping items that should be run together only one time
Connection Manager
A Connection Manager establishes the connection to the source and destination (database or file) with the necessary credentials needed. It is the Connection Manager that makes SSIS able to connect to any data source and copy it to any destination. Without the SSIS Connection Manager, there is no easy way to move data between disparate data sources and destinations.


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