With the rapid increase in popularity of mobile devices, a huge number of mobile applications are published with rich functionalities. However, the available functionalities still do not satisfy the variety of users' needs. Some common tasks cannot be accomplished by using an individual application, but require the interoperability of multiple applications. Unfortunately, most of the applications are not ready to be integrated due to the lack of formal descriptions of its offered functionalities. Accordingly, it becomes essential to describe the shared functionalities of mobile applications in a structured way. We address this problem by proposing an XML-based modeling language, called LIMA (Language for Interoperability of Mobile Applications), that allows developers to describe the shared functionalities of mobile applications. In order to enhance the interoperability, LIMA is designed to abstract the functionalities of mobile applications from the concrete details on how to invoke those functions. We demonstrate our modeling language by implementing a parser tool that generates proxy classes to leverage the mobile application development process. Moreover, we apply our modeling language with a mobile mashup approach to demonstrate automatic mobile application integration.