In this paper, we propose a supporting method for developments of Web applications in order to support communication between users and developers. Our method combines three-layer architecture modeling of Web application and knowledge sharing technologies based on ontologies. The ontologies, which are used in the method and called enterprise application ontology (EAO), enable users and developers to form common understanding about system specification. EAO covers three aspects (legal aspect, business process, and software design) of business which is a candidate of development of a Web application. EAO includes three ontologies constructed from each of the three aspects. Concepts and structure of EAO are applied on page transition models, which are called Web Process Architecture, of a Web application. As a case study, we applied our method for a development of a ledger accounting system in a local government. And we confirmed that our method could support the development on the business analysis phase.