The case for reflective middleware

Abstract

R ecent advances in distributed, mobile, and ubiquitous systems demand new computing environments characterized by a high degree of dynamism. Variations in resource availability, network connectivity, and hardware and software platforms influence the performance of the related user applications. The expected growth of ubiquitous computing over the next five years will further alter the nature of the computational infrastructure, bringing a plethora of small devices and requiring customized protocols and policies to fulfill users' evolving quality of service (QoS) requirements.During the past 10 years, software developers created middleware technology to facilitate development of software systems, most notably distributed and Internet-based, to support activities as diverse as scientific computation, information discovery and dissemination, and e-commerce. Middleware mediates interaction between the application and the operating system (hence its name). Related technologies, including the Object Management Group's CORBA, Sun Microsystems' Java-based J2EE, and Microsoft's .NET, hide from the pro-grammer the complicated details of network communication, remote method invocation, naming, and service instantiation, easing construction of complex distributed systems. CORBA, or Common Object Request Broker Architecture, and Java also hide the differences in the underlying software and hardware platforms, increasing portability and facilitating maintenance, as new versions of operating systems are released. Despite aiding development of distributed applications, conventional middleware technology lacks support for the dynamic aspects of the new computational infrastructure. Next-generation applications require middleware that can be adapted to changes in the environment and customized to fit into devices, from PDAs and sensors to powerful desktops and multicomputers [1,5]. Here, we reflect on how two independent research projects might influence the evolution of next-generation middleware. The reflective middleware model is a principled and efficient way of dealing with highly dynamic environments yet supports development of flexible and adaptive systems and applications.It's flexible and reconfigurable yet simple for programmers to use, notably for building dynamic distributed applications operating on the Net.

The JBoss Extensible Server

“…Researchers have recently advocated "working toward standards for reflective middleware" [17]. The JBoss experience suggests that reflective models based on JMX should be seriously considered as candidates to standardization not only within the network and systems management field, but in the more general Java middleware arena.…”

“…Researchers have presented compelling arguments for also exploiting these techniques within the middleware platform [4,17]. We claim that application servers themselves can (and should) be built in a component-based way, out of dynamically deployable components that provide middleware services to application components.…”

PerPos: A Translucent Positioning Middleware Supporting Adaptation of Internal Positioning Processes

“…Given information about device types or network infrastructures the handling of such dynamic aspects can be optimized, e.g., by selecting protocols that better fit the underlying network infrastructure. To address this problem, reflective middleware has been proposed, as described by Kon et al [9], to provide traditional transparency coupled with translucency and fine-grain control. Reflective middleware provides inspection of their internal state using reflective meta interfaces.…”

“…To provide translucency and adaptation the PerPos middleware is designed around the central idea of representing the steps of the actual positioning process explicitly as a graph based on the flow of information from sensors to application code. This representation constitutes a reflection mechanism [9] that allows application developers to control and extend the positioning process and for the design to fulfill the three requirements stated above. We do not provide the functionality of a generic reflective middleware, and in Section 4 we argue that careful design of what is exposed through reflection decreases the conceptual overhead involved when developers perform adaptations.…”

Modularizing communication middleware concerns using aspects

“…Reflective middleware systems rely on the application of reflection to achieve customizable, open, and adaptive middleware platforms [17]. For example, UIC CORBA supports the concept of personality, that allows users to specialize middleware systems according to the requirements of a given distributed application or domain [28].…”