Framework for middleware executed on mobile devices

Ubiquitous computing is an appealing research area today and most likely the future. It is about unobtrusive computer support of users in their everyday activities. This support is achieved by an omnipresence of computers and their ability to spontaneously form distributed computing systems, and to exchange and process information. Ambient Intelligence, which is an application of ubiquitous computing, became a strategic research direction of the Information Society Technology programme of the European Union to form a knowledge society. The objective of Ambient Intelligence is to make life more comfortable and safer. Distributed computing systems for ubiquitous computing are characterised by heterogeneity of the computers used. They range from small sized computers embedded into everyday items like cars, heaters, toasters and coffee cups, to high performance computers like servers and mainframes. They all connect spontaneously via wireless network technology, e.g. wireless local area networks (WLAN), Bluetooth, Universal Mobile Telecommunications System (UMTS), etc. This heterogeneity increases the complexity of distributed computing systems, and as such their programming. Middleware is a software technology concept and software, to reduce the complexity by abstracting from heterogeneity and providing a homogeneous layer on top of the different, heterogeneous computers used in distributed computing systems. Middleware provides unified access to the heterogeneous resources, functionalities, and computers it abstracts from. Distributed computing systems for ubiquitous computing are characterised by the spontaneous connection of computers. Traditional middleware is designed for distributed computing systems without spontaneous connections. Recently developed middleware follows the service oriented architecture concept that takes into consideration spontaneous connections. Middleware functionality is realised as services, which are independent software elements. The Wireless World Research Forum (WWRF) has described services that future middleware may provide. These services are hosted by a service execution environment. Yet, there is a lack of definition of such service execution environment. This dissertation contributes to middleware development for distributed computing systems in ubiquitous computing. The focus is on middleware and enabling technologies to implement middleware. Concepts for service discovery, service update, and contracts between services are presented. The concepts are provided in a framework that is designed specifically for realising middleware for distributed computing systems in ubiquitous computing. This framework, called Framework for Applications in Mobile Environments (FAME2), includes guidelines for service development, a proposal of a service execution environment, and support for different levels of access control to protect middleware from malicious use. The service execution environment of FAME2 features: • low resource use on resource limited mobile devices like cellular phones and embedded computers • reconfiguration of middleware by changing the set of services at the middleware’s runtime • an open interface to utilise virtually any service discovery solution to locate services in a distributed computing system • online-update functionality for corrective, perfective, and adaptive maintenance of middleware and middleware services An accompanying work is the Extensible Constraint Framework (ECF) that makes Design by Contract available in the context of FAME2. Design by Contract is a technology to increase the quality of software systems created from software elements by formulating contracts between them. ECF enables negotiation and refinement of these contracts.