In this chapter, we have learned how to use variables in BPEL and how to manipulate data. We have explained that, in BPEL, all variables store XML. They are not only used to hold the requests and responses for invoked services (partner links), but also to store other data related to the process state. We have seen that we can declare variables of three different types, message types, elements, and simple types.

To manipulate data, we use the <assign> activity. We have become familiar with the <assign> activity and have learned how to use different possibilities when copying data. Probably expressions are used most often. Expressions are written in XPath. We have also learned how to access variables from the expressions, how to validate variables, and how to use XSLT transformation to transform more complex schemas.

In the next chapter, we will learn about loops and conditions.