A web application interface using the web service technology is required for enabling the interaction of various web applications on different platforms. In this paper, Model Driven Architecture (MDA) and Service Oriented Architecture (SOA) are combined as an approach using Service-Oriented Development Method (SOD-M) to develop of web application interfaces. The development process is initiated by describing the business process in the computation independent models (CIM). Afterward, the functionalities and processing systems in the Platform Independent Models (PIM), based on a business process and data types in the existing applications, are expressed. Model transformations are applied to generate the Web service interfaces in Web Service Desription Language (WSDL) and Web Service Business Process Execution Language (WS-BPEL) in the Platform Specific Models (PSM). For a case study, we illustrated a web interface application called Simpel as an interface between two existing applications in University of Lampung (Unila). This study shows how the proposed approach helps to develop web application that invokes web service to enable the interoperability of two existing application.