As of today, building automation systems are present in almost any commercial building. They perform climate control, lightning control, access control, surveillance, and quite a few other tasks. As a result of their evolutionary development, building automation systems are divided into separate silos of disciplines that are not well integrated with each other. As of today, a variety of communication protocols, data models and engineering approaches are used by different vendors. Existing

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... rdized building automation protocols as BACnet or KNX allow integration of some disciplines on the communication level but fail to provide means for common description of devices, services and data on the semantic level. This means that building automation applications that span multiple disciplines require a high effort for development, engineering and maintenance. If devices from multiple vendors are integrated in one installation, a set of different engineering tools and vendor-specific knowledge is required. In the ITEA "Building as a Service" (BaaS) project we try to overcome these deficiencies and define a common way to develop, engineer, commission, operate and maintain building automation systems following a service oriented approach. The whole process will be supported by semantic models to reduce costs and time-tomarket, which is a quite new approach. In this paper we will present the current state of the work with special regard to domain modeling and model driven processes that are currently being specified for the BaaS platform.