Middleware Support for Self-aware Computing Systems

The implementation of a distributed self-aware computing system (SACS) typically requires a substantial software infrastructure. A middleware system with dedicated services for self-awareness and self-expression can therefore support the development of SACS applications. In this chapter we show the advantages of using a middleware system as the basis for a self-aware computing system. We identify requirements for middleware systems to support the development of self-aware applications. By providing facilities for communication, decoupling and transparency, middleware systems can provide essential features needed in SACS. We compare different middleware paradigms and their suitability to support self-awareness in distributed applications. We argue that the publish/subscribe paradigm is very well suited for this application area since it supports modularisation and decoupling. Units can be added to and removed from existing applications and may well be reused in new applications. Thus, SACS can be constructed by recombining existing publish/subscribe modules. In addition, we present details of publish/subscribe and introduce our middleware implementation called Ella. We describe how different aspects of a SACS and patterns for self-aware applications can be represented using Ella. We present different communication paradigms in Ella (broadcasting, peer2peer) as well as decoupling mechanisms provided by the middleware. We argue that SACS applications can be developed (i) faster, (ii) more efficiently and (iii) more reliable with Ella. Finally, Chapter 13 presents a self-aware and self-expressive multi-camera application which has been implemented with Ella.