Abstract: WS-BPEL is the standard for specifying and executing business processes by orchestrating Web Services. Abstract and executable processes are two kinds of BPEL processes that are defined in the BPEL standard. An abstract process can be used as a process template, which can be completed and made executable through "executable completion". The BPEL standard defines a set of rules that must be obeyed during such an executable completion. In this paper, we present an algorithm for validating whether an executable BPEL process is a valid executable completion of an abstract BPEL process. Our approach advances the existing XML comparison algorithms in a way that it takes the BPEL-specific characteristics into account and is optimized towards the validation of "executable completion" of abstract BPEL processes.