The author presents a comprehensive routing system for dispatching an object between action stops, finding the principals (on the basis of functional information), notifying them in turn when their action is required, and potentially relocating the routed object to their nodes. Additional mechanisms for nagging principles who forget to act on the object, reporting progress (or lack thereof) to other principles, handling routing exceptions, sharing action paths, and routing an object on a parallel path are discussed. The routing system is built as a generic service layer above object-support services. It is easy to use, flexible, and reliable.>

The problems of finding objects in large and wide-area networks where objects may change their location in volatile memory as well as on stable storage are presented. The authors discuss possible solutions and describe those adopted in the Hermes system (a corporate wide, real life office application). They have designed and developed a location-independent-invocation (LII) mechanism that combines finding with invocation, using temporal location information. The mechanism also updates the system's knowledge of an object's location as a side-effect of invocation and object migration. Assumptions about object mobility indicate that objects are likely to be found within a few propagations of an invocation. If they cannot be found in this way, stable-storage and name services are used to locate the object. The major contribution of this work is to show how LII can be achieved in a large and dynamic environment in which objects are supported by neither are operating system nor the programming language.>

A brief overview is presented of work on building a highly distributed office application based on mobile objects. The authors explain the techniques used to find the target of an invocation and describe how the technique is implemented. Location-independent invocation (LII) is presented as a conceptual service that is independent of any particular application, operating system, or programming language. LII completely removes remote call processing buildings from the view of application programmer. It is shown how LII can be implemented without language or system support in any environment that provides reliable interprocess communication. The indications for LII are studied, i.e. under what circumstances the proposed abstractions are beneficial. A description is given of an application domain in which LII is useful and the core services that support it. An object-finding algorithm is described. The relationship of LII to earlier work on object-finding and location independence is included.>

A retrospective view is presented of the Charlotte distributed operating system, a testbed for developing techniques and tools to solve computation-intensive problems with large-grain parallelism. The final version of Charlotte runs on the Crystal multicomputer, a collection of VAX-11/750 computers connected by a local area network. The kernel/process interface is unique in its support for symmetric, bidirectional communication paths (called links), and synchronous nonblocking communications. Several lessons were learned in implementing Charlotte. Links have proven to be a useful abstraction, but the primitives do not seem to be at quite the right level of abstraction. The implementation uses finite-state machines and a multitask kernel, both of which work well. It also maintains absolute distributed information which is more expensive that using hints. The development of high-level tools, particularly the Lynx distributed programming language, has simplified the use of kernal primitives and helps to manage concurrency at the process level.>