In this paper, we present the UbiSMART (Ubiquitous Service MAnagement and Reasoning archiTecture) framework that aims to provide a highly flexible context-aware service provision mechanism with modular deployment and shared knowledge base. Pervasive computing enables assistive environments with extensive possibilities, especially when seizing opportunities to enhance quality of life for ageing people with dementia. Much research effort has been put on building architectures for ambient assisted living with various scope of focus, e.g. sensor deployment, activity recognition, service provision or human- computer interaction. However, targeting a large scale deployment, we have to go steps further in term of integration and adaptability. In this paper, we focus mainly on the reasoning mechanisms performing user interface plasticity, i.e. context-aware adaptation of the interaction to create seamless user experience. This research work led to the implementation of an integrated demonstrator based on user requirements analysis performed in Peacehaven nursing home in Singapore.