How to Use Expression Shape
The Expression shape enables you to enter any XLANG/s expression you choose in your orchestration. For example, you can make a .NET call to run an external program, or simply manipulate the values of your orchestration variables.
While the Expression shape is quite flexible, it is not good practice to use it to perform high-level orchestration logic, which preferably would be visible in the orchestration drawing itself. In general, it is easier to understand and maintain your orchestrations if your Expression shapes contain simple and modular expressions.
To configure an Expression shape
If BizTalk Expression Editor is not visible, right-click the Expression shape and click Edit Expression or, in the Properties window, click the Ellipsis (...) button for the Expression property.
In BizTalk Expression Editor, create an expression to assign values. For more information, see Requirements and Limitations for Expressions.