Middleware for sensor networks aims to support the development of applications for large populations of wirelessly connected nodes capable of computation, communication, and sensing. We examine the purpose, functionality, and characteristics of such middleware.

Abstract. Publish/subscribe (pub/sub) is considered a valuable middleware architecture that proliferates loose coupling and leverages reconfigurability and evolution. Up to now, existing pub/sub middleware was optimized for static systems where users as well as the underlying system structure were rather fixed. We study the question whether existing pub/sub middleware can be extended to support mobile and location-dependent applications. We first analyze the requirements of such applications and distinguish two orthogonal forms of mobility: the system-centric physical mobility and an application-centric logical mobility (where users are aware that they are changing location). We introduce location-dependent subscriptions as a suitable means to exploit the power of the event-based paradigm in mobile applications. Briefly spoken, location-dependency refines a subscription to accept only events related to a mobile user's current location. Implementations for both forms of mobility are presented within the content-based pub/sub middleware Rebeca, drawing from its refined routing capabilities (namely, covering and merging).

Abstract. We present a hardware and software platform for rapid prototyping of augmented sensor network systems, which may be temporarily connected to a backend infrastructure for data storage and user interaction, and which may also make use of actuators or devices with rich computing resources that perform complex signal processing tasks. The use of Bluetooth as the wireless networking technology provides us with a rich palette of Bluetooth-enabled commodity devices, which can be used as actuators, infrastructure gateways, or user interfaces. Our platform consists of a Bluetooth-based sensor node hardware (the BTnode), a portable operating system component, and a set of system services. This paper gives a detailed motivation of our platform and a description of the platform components. Though using Bluetooth in wireless sensor networks may seem counterintuitive at first, we argue that the BTnode platform is indeed well suited for prototyping applications in this domain. As a proof of concept, we describe two prototype applications that have been realized using the BTnodes.

The EPCglobal Network, an emerging standard for RFID, aims to raise visibility in supply chains by enabling interested parties to query item-level data. To get there, however, a critical piece is yet missing: a Discovery Service to identify possibly unknown supply chain actors holding relevant data for specific EPC numbers of individual products. Unfortunately, the Discovery Service architecture as initially conceived by EPCglobal needs revision as it either infringes the confidentiality of participating companies or its use is limited to identifying only participants already known. Against this background, this paper first discuusses the limitations of the architecture under consideration by EPCglobal and presents an alternative, more adequate Discovery Service design. Our concept encourages participation in the network while ensuring information provider confidentiality. Secondly, we present a roadmap for extending the existing EPCglobal Network with two critical services: an automated contract negotiation service and a billing service.

Abstract-Event-driven programming is a popular paradigm for programming sensor nodes. It is based on the specification of actions (also known as event handlers) which are triggered by the occurrence of events. While this approach is both simple and efficient, it suffers from two important limitations. Firstly, the association of events to actions is static-there is no explicit support for adopting this association depending on the program state. Secondly, a program is split up into many distinct actions without explicit support for sharing information among these. These limitations often lead to issues with code modularity, complexity, and correctness. To tackle these issues we propose OSM, a programming model and language for sensor nodes based on finite state machines. OSM extends the event paradigm with states and transitions, such that the invocation of actions becomes a function of both the event and the program state. For removing the second limitation, OSM introduces state attributes that allow sharing of information among actions. They can be considered local variables of a state with support for automatic memory management. OSM specifications can be compiled into sequential C code that requires only minimal runtime support, resulting in efficient and compact systems.