IT-systems have an important role in an organization's business. Since business requirements and strategies change according to the surrounding world the system architecture must adapt to the prevalent situation and possible long and short-term changes. The architecture of a modern web application adjusts to the challenges of an organization's business requirements. Especially Windows applications create administrative problems because their maintenance binds human resources and also because their usage context is limited. The cost-effective solution is to modernize the user interface of a Windows application into a web application.

The objective of this master's thesis was to describe the reference architecture for modernizing the Windows application user interface into a web. The thesis was ordered by Logica Suomi Oy and it was conducted in a Proof of concept project. The purpose of the thesis was to identify widely used architecture models and methods which enable implementation of the modernization. Furthermore the objective was to identify the methods and software which enable the development and implementation of a cost-effective and high quality web application. A minor objective was to describe the enterprise architecture of an administrator application which was to be modernized.

The result of the thesis was a new reference architecture which can be used in a system development project, customer documentation, sales and marketing. Modern web technologies were presented in the reference architecture which enables the implementation of a web application where user experience corresponds to that of a Windows application. In addition the thesis resulted in obtaining the enterprise architecture of an administrator application where the most important results are the target state of the modernization and the system architecture of an application. The most important development targets are the modernization framework based on the reference architecture and defining, designing and implementing the evaluation metrics used in the modernization project. With the help of relevant metrics it can be discovered whether the modernization project corresponds to the business requirements and strategies of an organization.