If you have used SSIS packages for any involved ETL processes, you have inevitably encountered the need for dynamic capabilities. A dynamic package can reconfigure itself at runtime to do things like run certain steps conditionally, create a series of auto-generated filenames for export, or retrieve and set send-to addresses on an alert e-mail from a data table. Because dynamic changes are fairly common occurrences, developers and architects turn to expressions as they begin rolling out SSIS projects in their development shops.
This chapter attempts to provide a solid information base to get you up to speed on expressions. Here we will consolidate the common questions, answers, and best practices about expressions that we’ve heard and explained since the first release of SSIS. The good news is that expressions are easy to use and impressively powerful. As you read this chapter, you will not only gain an understanding about how expressions work but also gain some insight into how you can use variables and parameters to set up expressions on your current SSIS project.