In this paper, we present a framework for implicit service calls in data centric Peer to Peer Active XML language. Active XML is a language devoted to the management of distributed data by embedding Web service calls into XML document. The aim of implicit calls is to allow dynamic data sources discovey through dynamic services discovery and composition. Implicit service calls are based on the use of ontologies for describing the domain and functionality of services to call and an Active XML engine for calls evaluation. The evaluation process deals mainly with dynamic service composition. It consists in matching OWL-S descriptions contained in a query with service descriptions in a peer-to-peer network. Such a network is structured in such a way that peers with similar functionalities are grouped together and each peer makes itself acquainted with matching relationships between its inputs/outputs and those of other peers.