Currently, the software industry is demanding the construction of Web applications that are built integrating functionality from third party systems. Web Engineering methods are not properly dealing with this open strategy. Instead, they only provide methodological support for the implementation of isolated Web applications. The solutions that are based on a specific technology do not solve the integration problem at all. To provide an adequate solution we have to tackle with the integration issue at the problem space, avoiding ad-hoc solutions. We should provide a set of mechanisms that allow to model integration at a high level of abstraction, independently of the underlying technology in which these services are provided. Following the MDA principles, we present a model driven approach that makes a clear separation of concerns in the Web development process. Our method includes a step where the integration issue is introduced as a new concern. In this step we introduce mechanisms that allow us to specify and include external services (by means of a Services Model). Moreover, these external services can take part in the specification of a business process through the Business Process model.