Ubiquitous sensing fuses the concepts of intelligent systems with ubiquitous computing in the development of novel sensor web applications, whereby the interaction of multiple disparate autonomous artefacts is a key requirement. In this paper, we present SIXTH, which is a middleware infrastructure for Ubiquitous Sensing that facilitates, and supports, the development and deployment of Sensor Web applications. SIXTH has been designed to be extensible, with provisions for user definable data retention policies, custom sensor data representations, and custom sensor node representations, whilst still providing a rich set of default behaviours. Within SIXTH, support is provided for the development and interaction of applications that incorporate both physical and cyber (virtual server side) sensors. With a view to supporting intelligent, in network, interaction policies, whereby sensor nodes must negotiate and coordinate their behaviour, the system has been designed to operate in conjunction with Agent Factory Micro Edition (AFME). AFME is a minimised footprint intelligent agent platform designed for resource constrained devices. It is based on the standard Agent Factory platform, which was developed for desktop machines, and is representative of a class of agent systems, which are referred to as Agent Oriented Programming frameworks. The paper discusses a ubiquitous mapping application that was developed using the middleware.