Web services integration is one of key issues in many B2B applications. Yet, current approaches to this problem tend to use a general-purpose programming language, thus incur type mismatches between the type system of XML schema and the object-oriented type system. In this paper, we present a uniform method for integrating Web services. We propose an extension of XQuery, referred to as WSQuery, which can contain Web service calls. We first present the conceptual evaluation strategy of WSQuery programs. Then, for speeding up the evaluation, we propose to schedule Web service calls to exploit parallelism. We carry out dependency analysis to determine dependency relations among Web service calls. The for loops, if branches and unknown parameters pose particular challenges for dependency analysis and scheduling. We use unfolding techniques to deal with them.