XML is already a de facto industry standard for data exchange, it has from an early stage been embraced by database researchers, and it is gaining increasing interest from programming language researchers. The PLAN-X workshops aim at providing a meeting ground for researchers from the XML, programming language and database communities.

The research field of Agent-Oriented Software Engineering (AOSE) aims to find abstractions, languages, methodologies and toolkits for modeling, verifying, validating and prototyping complex applications conceptualized as Multiagent Systems (MASs). A very lively research sub-field studies how formal methods can be used for AOSE. This paper presents a detailed survey of six logic-based executable agent specification languages that have been chosen for their potential to be integrated in our ARPEGGIO project, an open framework for specifying and prototyping a MAS. The six languages are $\textsf{ConGolog}$, $\textsf{AGENT-0}$, the $\textsf{IMPACT}$ agent programming language, $\textsf{DyLOG}$, Concurrent $\textsf{METATEM}$ and ${\cal E}_{hhf}$. For each executable language, the logic foundations are described and an example of use is shown. A comparison of the six languages and a survey of similar approaches complete the paper, together with considerations of the advantages of using logic-based languages in MAS modeling and prototyping.

We describe the FC++ library, a rich library supporting functional programming in C++. Prior approaches to encoding higher order functions in C++ have suffered with respect to polymorphic functions from either lack of expressiveness or high complexity. In contrast, FC++ offers full and concise support for higher-order polymorphic functions through a novel use of C++ type inference. The FC++ library has a number of useful features, including a generalized mechanism to implement currying in C++, a “lazy list” class which enables the creation of “infinite data structures”, a subtype polymorphism facility, and an extensive library of useful functions, including a large part of the Haskell Standard Prelude. The FC++ library has an efficient implementation. We show the results of a number of experiments which demonstrate the value of optimizations we have implemented. These optimizations have improved the run-time performance by about an order of magnitude for some benchmark programs that make heavy use of FC++ lazy lists. We also make an informal performance comparison with similar programs written in Haskell.

This issue of the Journal of Functional Programming marks a point of transition. Our long-time Chief Editors, Simon Peyton Jones and Philip Wadler, are stepping down. Most of us are aware of the amazing research contributions that Simon and Phil have made to functional programming. But you may not be aware how much these two have put in behind the scenes.

A two-straight-legged walking mechanism with flat feet is designed and built to study the passive dynamic gait. It is shown that the mechanism having flat feet can exhibit passive dynamic walking as those with curved feet, but the walking efficiency is significantly lower. It is also shown that the balancing mass and its orientation are effective for controlling side-to-side rocking and yaw, which have significant effects on steady walking. The effects of various parameters on the gait patterns are also studied. lt is shown that changes in the ramp angle have the most dominant effect on the gait pattern as compared with the changes in the hip mass, ramp surface friction and size of the flat feet. More specifically, as the ramp angle increases, the step length increases while the range of the side-to side rocking angle decreases and the step length dictates the walking speed and the gravitational power. Another finding, is that adding a hip mass improves the walking efficiency by allowing the mechanism to walk on a flatter ramp. This research enables us to gain a better understanding of the mechanics of walking. Such an understanding will have a direct impact on better design of prostheses and on the active control aspects of bipedal robots.

The ambient logic is a modal logic that was proposed for the description of the structural and computational properties of distributed and mobile computation. The structural part of the ambient logic is, essentially, a logic of labelled trees, hence it turns out to be a good foundation for query languages for semistructured data, much in the same way as first-order logic is a fitting foundation for relational query languages. We define here a query language for semistructured data that is based on the ambient logic, and we outline an execution model for this language. The language turns out to be quite expressive. Its strong foundations and the equivalences that hold in the ambient logic are helpful in the definition of the language semantics and execution model.

This paper presents the basis of a mathematical model for simulation of planar flexible-link manipulators, taking into consideration the effect of higher stiffness zones at the link tips. The proposed formulation is a variation of the finite segment multi-body dynamics approach. The formulation employs a consistent mass matrix in order to provide better approximation than the traditional lumped masses often encountered in the finite segment approach. The formulation is implemented into a computational code and tested through three examples; cantilever beam, rotating beam and three-link manipulator. In these examples, the length of the rigid tips at both sides of each link ranges from 0% to 6.25% of the whole link length. The zones of higher stiffness at the link tips are treated as short rigid zones. The effect of the rigid zones is averaged along with some portions of the flexible links, thereby allowing further simplification of the dynamic equations of motion. The simulation results demonstrate the effectiveness of the proposed modeling technique and show the importance of not ignoring the effect of the rigid tips.

Nowadays concepts, languages and models for coordination cannot leave aside the needs of the increasing number of commercial applications based on global computing over the (inter)net. For example, platforms like Microsoft .NET and Sun Microsystems Java come equipped with packages for supporting ad hoc transactional features, which are essential for most business applications. We show how to extend the coordination language par excellence (viz. Linda) with basic primitives for transactions, while retaining a formal model for its concurrent computations. This is achieved by exploiting a variation of Petri nets, called zero-safe nets, where transactions can be suitably modelled by distinguishing between stable places (ordinary ones) and zero places (where tokens can only be temporarily allocated, defining hidden states). The relevance of the transaction mechanism is illustrated in terms of expressive power. Finally, it is shown that stable places and transactions viewed as atomic steps define an abstract semantics that is apt for a fully algebraic treatment, as demonstrated via categorical adjunctions between suitable categories of nets.

Ball passing is an elementary and frequently employed human soccer skill. This paper examines the realization and visualization of ball passing, a low level move-to-ball behavior of a soccer robot, in a robot soccer game. A case study of three mechanically identical mobile robots with a formation ready to pass a ball cyclically in a zigzag pattern is examined. We build a control command driven mobile robot motion simulator with a controller and dynamics of mobile robots, not only nonholonomic kinematic constraints to simulate the motion of a soccer robot driven by wheels torques to generate wheels accelerations, to update the robot position and orientation at successive time instants. Kick motion follows a physical law, and a simplified collision check and response model is utilized for the efficient detection of the hitting a robot with the ball or other robots. The realization of specific ball passing strategy to drive each soccer robot in a position to receive a pass includes three levels of organization, coordination, and execution: careful integrated design of a dynamic formation and role change scheme, ball position estimation, and coordinated trajectory (i.e. path and velocity) planning and tracking control. Simulations are performed to illustrate the feasibility of the realization of ball passing among three robots, implemented by a software program for coordinated trajectory planning and tracking control in the developed simulator.

It is reported by the British Aerospace (BAE Systems) that their researchers have developed a revolutionary airborne computer system that, they claim, can land aircraft safely without the need of human air traffic controllers. The new system will allow a pilot to determine an aircraft's landing by pressing a button in the cockpit to initiate the computer system.

This paper explores a new type of a parallel platform human interface manipulator based on virtual reality (VR) for mechanism design applications. A motion control of a six-link robot manipulator actuated by three active joints is presented here. The main components of the system include a user interface, a software simulating the environment, and a VR control system. The model of the VR system is built based on a force feedback behavior that enables the operator to feel the actual force feedback from the virtual environment just as he/she would from the real environment. A primary stabilizing controller is used to develop a haptic interface device where realistic simulations of the dynamic interaction forces between a human operator and the simulated virtual object/mechanism is required. The stability and performance of the system are studied and analyzed based on the Nyquist stability criterion. Experiments on cutting virtual clay are used to validate the theoretical developments. It was shown that the experimental and theoretical results are in good agreement.

In this paper, we propose a new method to learn a multi-fingered hand grasping posture with little knowledge about the task and few sensing capabilities. The developed model is composed of two stages. The first is dedicated to the finger inverse kinematics learning in order to provide the fingertip-desired position. This function is fulfilled by modular neural network architecture. Following the concept of reinforcement learning, a second neural model dealing with noisy sensing information is used to search the space of hand configuration. Simulation results show a good learning of grasping postures with five fingers and different noise levels.