A conversation protocol is a top-down specification framework which specifies desired global behaviors of a web service composition. In our earlier work [6] we studied the problem of realizability, i.e., given a conversation protocol, can a web service composition be synthesized to generate behaviors as specified by the protocol. Several sufficient realizability conditions were proposed in [6] to ensure realizability. Conversation protocols studied in [6], however, are essentially abstract control flows without data semantics. This paper extends the work in [6] and achieves more accurate analysis by considering data semantics. To overcome the state-space explosion caused by the data content, we propose a symbolic analysis technique for each realizability condition. In addition, we show that the analysis of the autonomy condition can be done using an iterative refinement approach.