Service substitution : a behavioral approach based on Petri Nets

Service-Oriented Computing is an emerging computing paradigm that supports the modular design of (software) systems. Complex systems are designed by composing less complex systems, called services. Such a (complex) system is a distributed application often involving several cooperating enterprises. As a system usually changes over time, individual services will be substituted by other services. Substituting one service by another one should not affect the correctness of the overall system. Assuring correctness becomes particularly challenging, as the services rely on each other, and each of the involved enterprises only oversees a part of the overall system. In addition, services communicate asynchronously which makes the analysis even more difficult. For this reason, formal methods to support service substitution are indispensable. In this thesis, we study service substitution at the level of service models. Thereby we restrict ourselves to service behavior. As a formalism to model service behavior, we use Petri nets. The first contribution of this thesis is the definition of several substitutability criteria that are suitable in the context of Service-Oriented Computing. Substituting a service S by a service S0 should preserve some behavioral properties of the overall system. For each set of behavioral properties and a given service S, there exists a set of behaviorally compatible services for S. A substitutability criterion defines which of these behaviorally compatible services of S have to be preserved by S0. We relate our substitutability criteria to preorders and equivalences known from process theory. The second contribution of this thesis is to present, for each substitutability criterion, a procedure to decide whether a service S0 can substitute a service S. The decision requires the comparison of the in general infinite sets of behaviorally compatible services for the services S and S0. Hence, we extend existing work on an abstract representation of all behaviorally compatible services for a given service. For each notion of behavioral compatibility, we present an algorithmic solution to represent all behaviorally compatible services. Based on these representations, we can decide substitutability of a service S by a service S0. The third contribution of this thesis is a method to support the design of a service S0 that can substitute a service S according to a substitutability criterion. Our approach is to derive a service S0 from the service S by stepwise transformation. To this end, we present several transformation rules. Finally, we formalize and we extend the equivalence notion for services specified in the language WS-BPEL. That way, we demonstrate the applicability of our work

Tax Rates and Economic Growth

[Excerpt] This report summarizes the evidence on the relationship between tax rates and economic growth, referring in a number of cases to more-detailed CRS reports. Potentially negative effects of tax rates on economic growth have been an issue in the debate about whether to increase taxes to address the budget deficit and whether to broaden the base and lower the rates with tax reform. After first distinguishing between short-run counter-cyclical considerations and long-run growth effects, the following section provides some historical data on tax rates and measures of factor supply and growth. This report then reviews the empirical evidence on the major contributors to growth. The final section concludes with a review of dynamic scoring issues

Opening-up the objective function: choice behavior and economic and non-economic variables—core and marginal altruism

A revised model of the preference function is presented incorporating utility maximizing acts of material self-sacrifice. This model incorporates neoclassical and behavioral arguments, allowing for the stylized fact that economic agents are motivated by both material and non-material incentives. Given such a preference function, choice behavior is modeled as a function of relative opportunity costs (price) and real income. Preferences are determined by a variety of variables inclusive of social capital and education. There is therefore a core preference based upon non-economic variables and a ‘marginal' component which is a function of conventional economic variables. The relative importance of these two components in determinating choice behavior is an empirical question. Building upon conventional tools, a demand curve for moral acts is derived and underlying income and substitution effects discussed. Empirical evidence from the tipping literature is used to illustrate the model.

Global HIV Prevention Progress Report Card 2010

Assesses progress in terms of data quality and outcome on the working group's recommendations including on prevention strategies, information systems, funding, policy, transparency, evidence-based approaches, technical support, research, and advocacy

Analytical Modeling Framework to Assess the Economic and Environmental Impacts of Residential Deliveries, and Evaluate Sustainable Last-Mile Strategies

In the last decade, e‐commerce has grown substantially, increasing business‐to‐business, business‐to‐consumer, and consumer‐to‐consumer transactions. While this has brought prosperity for the e-retailers, the ever-increasing consumer demand has brought more trucks to the residential areas, bringing along externalities such as congestion, air and noise pollution, and energy consumption. To cope with this, different logistics strategies such as the introduction of micro-hubs, alternative delivery points, and use of cargo bikes and zero emission vehicles for the last mile have been introduced and, in some cases, implemented as well. This project, hence, aims to develop an analytical framework to model urban last mile delivery. In particular, this study will build upon the previously developed econometric behavior models that capture e-commerce demand. Then, based on continuous approximation techniques, the authors will model the last-mile delivery operations. And finally, using the cost-based sustainability assessment model (developed in this study), the authors will estimate the economic and environmental impacts of residential deliveries under different city logistics strategies.View the NCST Project Webpag

The Effect of Base-Broadening Measures on Labor Supply and Investment: Considerations for Tax Reform

[Excerpt] This report attempts to show how options to broaden the tax base by placing limitations on itemized deductions can potentially work against the expansionary effects of reducing marginal tax rates. After base-broadening tax reform taxpayers may face lower statutory marginal rates but some taxpayers—those who itemize—may have more of their income is subject to tax, effectively increasing their marginal tax rates. The report also addresses other common base-broadening provisions that increase the effective marginal tax rate on the return to capital

International Corporate Tax Rate Comparisons and Policy Implications

[Excerpt] This report focuses on the global issues relating to tax rate differentials between the United States and other countries. It provides tax rate comparisons; discusses policy implications, including the effect of a corporate rate cut on revenue, output, and national welfare; and discusses the outlook for and consequences of a revenue neutral corporate tax reform

HIV vulnerability of men and women who inject drugs in Kumasi, Ghana

This study was implemented by Boston University in collaboration with the Kwame Nkrumah University of Science and Technology with support from the President’s Emergency Plan for AIDS Relief (PEPFAR) through the U.S. Agency for International Development under Project SEARCH Task Order No. GHH‐I‐00‐07‐00023‐00, beginning August 27, 2010. The content and views expressed here are the authors’ and do not necessarily reflect the opinion or policy of USAID or the U.S. Government.Reducing vulnerability to HIV infection among key populations in Ghana is a major goal for the National AIDS Control Program (NACP) and the GAC. While a number of studies have explored HIV risk behaviours among several key vulnerable populations in Ghana including female sex workers, men who have sex with men, and prisoners, little is known about the drug use and sexual vulnerability of people who inject drugs (PWID). In addition, no programs have been implemented to reduce the vulnerability among this population. This report provides the findings from a qualitative study that aimed to understand the social, economic and behavioral vulnerability to HIV of PWID in Kumasi and to inform the development and implementation of HIV prevention programs for this population. The research was conducted by a collaborative team comprised of researchers from Boston University’s Center for Global and Health and Development (CGHD) and the Kwame Nkrumah University of Science and Technology (KNUST) School of Medical Sciences. It is one of nine studies under the Operations Research on Key Populations project funded by the United States Agency for International Development (USAID). The study was designed and carried out in collaboration with the Ghana AIDS Commission (GAC).Support from the President’s Emergency Plan for AIDS Relief (PEPFAR) through the U.S. Agency for International Development under Project SEARCH Task Order No. GHH‐I‐00‐07‐00023‐00, beginning August 27, 201

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