The primary goal of this research is to propose a novel approach for developing a federated information system of document management applications, which we call SoDOCM (Service-Oriented Document Management) system. The SoDOCM system is a mediator-based federated Information System that is designed and developed based upon the four-level service schema architecture concept, which is a variant of the five-level schema architecture for Federated Database Systems. By modeling the fivelevel schema architecture in terms of service-oriented computing paradigm, four-level service schema architecture is proposed as the central concept for integrating heterogeneous multiple document managements systems. Three different service types such as atomic, simple, and composite services are employed to make the heterogeneous multi-document management system interoperable since standard interfaces and interaction protocols of web services can be supported in a loosely coupled fashion. Representation schemes for schemata at each level are defined by using XML based web services and schema description languages. Several functions such as service request, discovery, composition, publishing, and invocation are proposed and implemented for the mapping between different schema levels.