Structuring process logic
BPEL provides the means to structure the business logic according to your needs. If you need a number of activities executed in a sequential order (e.g. first receive the order, then check the payment, then ship the goods, then send a confirmation) you can do so by using BPEL’s sequence activity. In other words, the sequence activity is used to define a collection of activities which are executed sequentially in lexical order.
Another activity used for structuring the business logic is the if-else activity. The construct might be known from traditional programming languages. The if-else activity allows you to select exactly one branch of the activity from a given set of choices. For each choice, the behavior is to check a condition and if that condition evaluates to true, the associated branch is executed, otherwise an alternative path is taken. As with all expressions in BPEL, you can use XPath expressions to formulate your condition. Note that only the first branch with a true condition is executed. If no condition evaluates to true, then a default choice can be specified using the else branch.