844 research outputs found
Scalable Co-Optimization of Morphology and Control in Embodied Machines
Evolution sculpts both the body plans and nervous systems of agents together
over time. In contrast, in AI and robotics, a robot's body plan is usually
designed by hand, and control policies are then optimized for that fixed
design. The task of simultaneously co-optimizing the morphology and controller
of an embodied robot has remained a challenge. In psychology, the theory of
embodied cognition posits that behavior arises from a close coupling between
body plan and sensorimotor control, which suggests why co-optimizing these two
subsystems is so difficult: most evolutionary changes to morphology tend to
adversely impact sensorimotor control, leading to an overall decrease in
behavioral performance. Here, we further examine this hypothesis and
demonstrate a technique for "morphological innovation protection", which
temporarily reduces selection pressure on recently morphologically-changed
individuals, thus enabling evolution some time to "readapt" to the new
morphology with subsequent control policy mutations. We show the potential for
this method to avoid local optima and converge to similar highly fit
morphologies across widely varying initial conditions, while sustaining fitness
improvements further into optimization. While this technique is admittedly only
the first of many steps that must be taken to achieve scalable optimization of
embodied machines, we hope that theoretical insight into the cause of
evolutionary stagnation in current methods will help to enable the automation
of robot design and behavioral training -- while simultaneously providing a
testbed to investigate the theory of embodied cognition
Management of object-oriented action-based distributed programs
Phd ThesisThis thesis addresses the problem of managing the runtime behaviour of distributed
programs. The thesis of this work is that management is fundamentally
an information processing activity and that the object model, as applied to actionbased
distributed systems and database systems, is an appropriate representation
of the management information. In this approach, the basic concepts of classes,
objects, relationships, and atomic transition systems are used to form object
models of distributed programs. Distributed programs are collections of objects
whose methods are structured using atomic actions, i.e., atomic transactions.
Object models are formed of two submodels, each representing a fundamental
aspect of a distributed program. The structural submodel represents a static
perspective of the distributed program, and the control submodel represents a
dynamic perspective of it. Structural models represent the program's objects,
classes and their relationships. Control models represent the program's object
states, events, guards and actions-a transition system. Resolution of queries on
the distributed program's object model enable the management system to control
certain activities of distributed programs.
At a different level of abstraction, the distributed program can be seen as a
reactive system where two subprograms interact: an application program and a
management program; they interact only through sensors and actuators. Sensors
are methods used to probe an object's state and actuators are methods used
to change an object's state. The management program is capable to prod the
application program into action by activating sensors and actuators available at
the interface of the application program. Actions are determined by management
policies that are encoded in the management program. This way of structuring
the management system encourages a clear modularization of application and
management distributed programs, allowing better separation of concerns. Managemental
concerns can be dealt with by the management program, functional
concerns can be assigned to the application program.
The object-oriented action-based computational model adopted by the management
system provides a natural framework for the implementation of faulttolerant
distributed programs. Object orientation provides modularity and extensibility
through object encapsulation. Atomic actions guarantee the consistency of
the objects of the distributed program despite concurrency and failures. Replication
of the distributed program provides increased fault-tolerance by guaranteeing
the consistent progress of the computation, even though some of the replicated
objects can fail.
A prototype management system based on the management theory proposed
above has been implemented atop Arjuna; an object-oriented programming system
which provides a set of tools for constructing fault-tolerant distributed programs. The management system is composed of two subsystems: Stabilis, a
management system for structural information, and Vigil, a management system
for control information. Example applications have been implemented to illustrate
the use of the management system and gather experimental evidence to give
support to the thesis.CNPq (Consellho Nacional de Desenvolvimento Cientifico e Tecnol6gico, Brazil):
BROADCAST (Basic Research On Advanced Distributed Computing: from Algorithms to SysTems)
Processing Structured Hypermedia : A Matter of Style
With the introduction of the World Wide Web in the early nineties, hypermedia has become the uniform interface to the wide variety of information sources available over the Internet. The full potential of the Web, however, can only be realized by building on the strengths of its underlying research fields. This book describes the areas of hypertext, multimedia, electronic publishing and the World Wide Web and points out fundamental similarities and differences in approaches towards the processing of information. It gives an overview of the dominant models and tools developed in these fields and describes the key interrelationships and mutual incompatibilities. In addition to a formal specification of a selection of these models, the book discusses the impact of the models described on the software architectures that have been developed for processing hypermedia documents. Two example hypermedia architectures are described in more detail: the DejaVu object-oriented hypermedia framework, developed at the VU, and CWI's Berlage environment for time-based hypermedia document transformations
Adaptive object management for distributed systems
This thesis describes an architecture supporting the management of pluggable software components and evaluates it against the requirement for an enterprise integration platform for the manufacturing and petrochemical industries. In a distributed environment, we need mechanisms to manage objects and their interactions. At the least, we must be able to create objects in different processes on different nodes; we must be able to link them together so that they can pass messages to each other across the network; and we must deliver their messages in a timely and reliable manner. Object based environments which support these services already exist, for example ANSAware(ANSA, 1989), DEC's Objectbroker(ACA,1992), Iona's Orbix(Orbix,1994)Yet such environments provide limited support for composing applications from pluggable components. Pluggability is the ability to install and configure a component into an environment dynamically when the component is used, without specifying static dependencies between components when they are produced. Pluggability is supported to a degree by dynamic binding. Components may be programmed to import references to other components and to explore their interfaces at runtime, without using static type dependencies. Yet thus overloads the component with the responsibility to explore bindings. What is still generally missing is an efficient general-purpose binding model for managing bindings between independently produced components. In addition, existing environments provide no clear strategy for dealing with fine grained objects. The overhead of runtime binding and remote messaging will severely reduce performance where there are a lot of objects with complex patterns of interaction. We need an adaptive approach to managing configurations of pluggable components according to the needs and constraints of the environment. Management is made difficult by embedding bindings in component implementations and by relying on strong typing as the only means of verifying and validating bindings. To solve these problems we have built a set of configuration tools on top of an existing distributed support environment. Specification tools facilitate the construction of independent pluggable components. Visual composition tools facilitate the configuration of components into applications and the verification of composite behaviours. A configuration model is constructed which maintains the environmental state. Adaptive management is made possible by changing the management policy according to this state. Such policy changes affect the location of objects, their bindings, and the choice of messaging system
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