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Abstract:Object-based middleware systems, like CORBA, provide the basis for object-based distributed applications. For aspects concerning distributed programming an aspect weaver has to generate code which interacts with the middleware system. As parts of these aspects often have to be implemented on top of the middleware, weavers are very dependent on the middleware system and on the implementations on top of it. This paper introduces a middleware called AspectIX that provides aspects as a generic mechanism to implement and control nonfunctional properties of a distributed object (e.g., properties related to the communication mechanisms used for a distributed object or the consistency policies between replicated data parts of the distributed objects). AspectIX provides an open and generic interface to all of these nonfunctional aspects. Aspect configuration can be controlled and changed at run-time with an immediate effect on the distributed object.The AspectIX architecture allows implementations of a distributed AspectIX object to be dynamically replaced in order to fulfill a new aspect configuration. Thus, an AspectIX implementation is also open for new aspects.

Abstract:Quality of service is becoming more and more important in distributed systems. Current middleware systems lack quality-of-service support on the application and on the system level. AspectIX is a CORBA-compliant middleware platform that defines generic interfaces to control quality-of-service and an infrastructure for quality implementations.AspectIX is based on a fragmented object model that can provide transparent client-side quality implementations. Quality implementations can be weaved into functional fragments using a hierarchy of Weavelets which are modular code-transforming software components. A distributed policy decision engine allows administrators to influence object-internal decisions, e.g., decisions about how to implement the current quality-of-service requirements.

Globally distributed services need more than location transparency. An implementation of such a service has to scale to millions of users from all over the world. Those users may have different and varying quality-of-service requirements that have to be considered for an appropriate distribution and installation of service components. The service also has to scale to thousands of administrative domains hosting those components. AspectIX is a novel middleware architecture which extends CORBA by a partitioned object model. A globally distributed service can be completely encapsulated into a single distributed object which contains not only all necessary components for scalability (e.g., caches and replicas) but also the knowledge for selforganization and distribution of the service. For distribution and installation of components, the service considers object-external policies to achieve administrative scalability.

CORBA as a standardized object-based middleware for distributed computing still lacks sufficient support for mobility and replication, although there are several proposals to integrate these mechanisms. AspectIX is a more flexible and more open architecture than CORBA, but AspectIX is still fully CORBA compliant.Unlike CORBA with its static client-server relationship, AspectIX uses the concept of distributed objects. Each distributed object is represented by at least one local part, called fragment, that communicates with other fragments to synthesize the desired behaviour. The fragment implementation that is actually used depends on nonfunctional aspects which are specified on the distributed object via a typed interface. Based on this model AspectIX provides a single mechanism that is especially suited to realize both: mobility and replication.