In proactive computing, systems can act to eliminate, mitigate or take advantage of previous knowledge to manipulate situations of interest in advance. Such behavior is critical for Ambient Assisted Living Systems. In this paper, we present semantic models to design and implement proactive systems to Home Care environments implemented with devices and sensors. These models support semantic interoperability between the physical environments and different software levels allowing the identification of the user context. Proactivity is then obtained by the construction of the most suitable action's plan that results from the consumption of services provided by these devices and services. One challenge is to model a high-level situation and select the particular device that best meets users' needs, considering their context, location, and disabilities. The paper describes the steps required to create a generic, flexible and modularized model that can be extended to incorporate new domain knowledge regarding the specific requirements of different Ambient Assisted Living Systems.