Tau Be or not Tau Be? - A Perspective on Service Compatibility and Substitutability

One of the main open research issues in Service Oriented Computing is to propose automated techniques to analyse service interfaces. A first problem, called compatibility, aims at determining whether a set of services (two in this paper) can be composed together and interact with each other as expected. Another related problem is to check the substitutability of one service with another. These problems are especially difficult when behavioural descriptions (i.e., message calls and their ordering) are taken into account in service interfaces. Interfaces should capture as faithfully as possible the service behaviour to make their automated analysis possible while not exhibiting implementation details. In this position paper, we choose Labelled Transition Systems to specify the behavioural part of service interfaces. In particular, we show that internal behaviours (tau transitions) are necessary in these transition systems in order to detect subtle errors that may occur when composing a set of services together. We also show that tau transitions should be handled differently in the compatibility and substitutability problem: the former problem requires to check if the compatibility is preserved every time a tau transition is traversed in one interface, whereas the latter requires a precise analysis of tau branchings in order to make the substitution preserve the properties (e.g., a compatibility notion) which were ensured before replacement.Comment: In Proceedings WCSI 2010, arXiv:1010.233

Dynamic homogenisation of Maxwell’s equations with applications to photonic crystals and localised waveforms on gratings

A two-scale asymptotic theory is developed to generate continuum equations that model the macroscopic be- haviour of electromagnetic waves in periodic photonic structures when the wavelength is not necessarily long relative to the periodic cell dimensions; potentially highly-oscillatory short-scale detail is encapsulated through integrated quantities. The resulting equations include tensors that represent effective refractive indices near band edge frequencies along all principal axes directions, and these govern scalar functions providing long-scale mod- ulation of short-scale Bloch eigenstates, which can be used to predict the propagation of waves at frequencies outside of the long wavelength regime; these results are outside of the remit of typical homogenisation schemes. The theory we develop is applied to two topical examples, the first being the case of aligned dielectric cylin- ders, which has great importance in modelling photonic crystal fibres. Results of the asymptotic theory are veri- fied against numerical simulations by comparing photonic band diagrams and evanescent decay rates for guided modes. The second example is the propagation of electromagnetic waves localised within a planar array of di- electric spheres; at certain frequencies strongly directional propagation is observed, commonly described as dy- namic anisotropy. Computationally this is a challenging three-dimensional calculation, which we perform, and then demonstrate that the asymptotic theory captures the effect, giving highly accurate qualitative and quantitative comparisons as well as providing interpretation for the underlying change from elliptic to hyperbolic behaviour

Reactivity on the Web

Reactivity, the ability to detect simple and composite events and respond in a timely manner, is an essential requirement in many present-day information systems. With the emergence of new, dynamic Web applications, reactivity on the Web is receiving increasing attention. Reactive Web-based systems need to detect and react not only to simple events but also to complex, real-life situations. This paper introduces XChange, a language for programming reactive behaviour on the Web, emphasising the querying of event data and detection of composite events

A semantical framework for the orchestration and choreography of web services

Web Services are software services that can be advertised by providers and invoked by customers using Web technologies. This concept is currently carried further to address the composition of individual services through orchestration and choreography to services processes that communicate and interact with each other. We propose an ontology framework for these Web service processes that provides techniques for their description, matching, and composition. A description logic-based knowledge representation and reasoning framework provides the foundations. We will base this ontological framework on an operational model of service process behaviour and composition

Dynamic Factor Analysis for Measuring Money

Technological innovations in the financial industry pose major problems for the measurement of monetary aggregates. The authors describe work on a new measure of money that has a more satisfactory means of identifying and removing the effects of financial innovations. The new method distinguishes between the measured data (currency and deposit balances) and the underlying phenomena of interest (the intended use of money for transactions and savings). Although the classification scheme used for monetary aggregates was originally designed to provide a proxy for the phenomena of interest, it is breaking down. The authors feel it is beneficial to move to an explicit attempt to measure an index of intended use. The distinction is only a preliminary step. It provides a mechanism that allows for financial innovations to affect measured data without fundamentally altering the underlying phenomena being measured, but it does not automatically accommodate financial innovations. To achieve that step will require further work. At least intuitively, however, the focus on an explicit measurement model provides a better framework for identifying when financial innovations change the measured data. Although the work is preliminary, and there are many outstanding problems, if the approach proves successful it will result in the most fundamental reformulation in the way money is measured since the introduction of monetary aggregates half a century ago. The authors review previous methodologies and describe a dynamic factor approach that makes an explicit distinction between the measured data and the underlying phenomena. They present some preliminary estimates using simulated and real data.Econometric and statistical methods; Monetary aggregates; Monetary and financial indicators

FTT:Power : A global model of the power sector with induced technological change and natural resource depletion

This work introduces a model of Future Technology Transformations for the power sector (FTT:Power), a representation of global power systems based on market competition, induced technological change (ITC) and natural resource use and depletion. It is the first component of a family of sectoral bottom-up models of future technology transformations, designed to be integrated into the global macroeconometric model E3MG. ITC occurs as a result of technological learning as given by cumulative investment and leads to highly nonlinear, irreversible and path dependent technological transitions. The model makes use of a dynamic coupled set of logistic differential equations. As opposed to traditional bottom-up energy models based on systems optimisation, logistic equations offer an appropriate treatment of the times and rates of change involved in sectoral technology transformations. Resource use and depletion are represented by local cost-supply curves, which give rise to different regional energy landscapes. The model is explored using two simple scenarios, a baseline and a mitigation case where the price of carbon is gradually increased. While a constant price of carbon leads to a stagnant system, mitigation produces successive technology transitions leading towards the gradual decarbonisation of the global power sector.This work was supported by the Three Guineas TrustSubmitted for publication to Energy Polic

Dynamic analysis of the vehicle-structure interaction: a direct and efficient computer implementation

The simulation of the dynamic behavior of a structure subjected to sets of moving loads originated by vehicles whose structural behavior is also considered corresponds to a task not efficiently addressed by standard finite element packages. The capability of solving this type of problems has been introduced in the FEMIX 4.0 computational code by means of an integrated formulation, which includes equilibrium and compatibility equations, with unknowns that consist on displacements and interaction forces. Each system of linear equations is efficiently solved by considering the characteristics of each submatrix of the coefficient matrix