As you’ve probably noticed, SSIS variables and expressions often go hand in hand. Expressions can be used in many different parts of a package, including tasks, containers, precedence constraints, and connection managers. These items support having expressions applied to one of their properties. For example, a File connection manager can use an expression to set its ConnectionString property.
Developers can add expressions on most—but not all—properties of most—but not all—package items. Selecting the Expression property in the Properties window and clicking on the ellipsis button opens up an editor dialog box where the developer can select a property and then build an expression for that property.
Expressions are incredibly powerful, ...