In ubiquitous environments, an application should adapt its behaviors in real time depending on its context and user?s needs that can be described by the notion of high-level goals. In this paper, goals are used to guide the automatic assembly of a context-aware application from service components on the fly. A lightweight architecture LCASOA based on OSGi (Open Services Gateway Initiative) is proposed to resolve goals, as well as support context acquisition, discovery and reasoning. It also provides a sophisticated service composition mechanism for the service-oriented architecture. A Context Pair Language and the production rule are used as semantic basis to model and express contextual information and goals. A prototype for telematics system is developed to demonstrate the schema's usefulness.