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

Operating guidelines for services

In the paradigm of service-oriented computing, companies organize their core competencies as services and may request other functionalities from services of other companies. Services provide high flexibility, platform independent loose coupling, and distributed execution. They may thus help to reduce the complexity of dynamically binding and integrating heterogenous processes within and across organizations. The vision of service-oriented architectures is to provide a framework for publishing new services, for on demand searching for and discovery of existing services, and for dynamically binding services to achieve common business goals. That way, each individual organization gains more flexibility to dynamically react on new challenges. As services may be created or modified, or collaborations may be restructured at any point in time, a new challenge arises in this setting—the challenge for deciding the compatibility of the composed services before their actual binding. Recent literature distinguishes four different aspects of service compatibility: syntactical, behavioral, semantical, and non-functional compatibility. In this thesis, we focus on behavioral compatibility and abstract from the other aspects. Potential behavioral incompatibilities between services include deadlocks (two services wait for a message of each other), livelocks (two services keep exchanging messages without progressing), and pending messages that have been sent but cannot be received anymore. For stateful services that interact via asynchronous message passing, deciding behavioral compatibility is far from trivial. Local changes to one service may introduce errors in some or even all other services of an interaction. The verification of behavioral compatibility suffers from state explosion problems and is restricted by privacy issues. That is, the parties of an interaction are essentially autonomous and may be competitors in other business fields. Consequently, they do not want to reveal the internals of their processes to the other participants in order to hide trade secrets. To systematically approach this challenge, we introduce a formal framework based on Petri nets and automata for service modeling and formalize behavioral compatibility as deadlock freedom of the composition of the services. The main contribution of this thesis is to introduce the concept of the operating guideline of a service. Operating guidelines provide a formal characterization of the set of all behaviorally compatible services R for a given service S. Usually, this set is infinite. However, the operating guideline OGS of a service S serves as a finite representation of this infinite set. Furthermore, the operating guideline of S reveals only internals that are inevitably necessary to decide behavioral compatibility with S. We provide a construction method of operating guidelines for finite-state services with bounded communication. Operating guidelines can be used in many applications in the context of serviceoriented computing. The most fundamental application is to support the discovery of behaviorally compatible services. To this end, we develop a matching procedure that efficiently decides whether a given service R is characterized by the operating guideline OGS of a service S. If R matches, then both services R and S are behaviorally compatible and can be bound together to interact with each other. If R does not match with OGS, then the services are behaviorally incompatible and may run into severe behavioral errors and not reach their common business goal. Operating guidelines can furthermore be applied in the novel research areas of service substitutability and the generation of adapter services, for instance. To this end, we develop methods to compare the sets of services characterized by the operating guidelines OGS and OGS0 . If OGS0 characterizes more services than OGS, then the service S can be substituted by the service S0 without loosing any behaviorally compatible interaction partner R. Furthermore, we show how to synthesize a service R from the operating guideline OGS such that R is behaviorally compatible to S by construction. All results presented in this thesis are implemented in our service analysis tool Fiona. Fiona may compute operating guidelines for services modeled as Petri nets. It may match a service with an operating guideline, compare operating guidelines for equivalence or an inclusion relation, and synthesize service adapters for behaviorally incompatible services. Together with the tool BPEL2oWFN— which translates web services specified in BPEL into Petri net models of the services—we can immediately apply our results to services that stem from practic

Closing the gap between guidance and practice, an investigation of the relevance of design guidance to practitioners using object-oriented technologies

This thesis investigates if object oriented guidance is relevant in practice, and how this affects software that is produced. This is achieved by surveying practitioners and studying how constructs such as interfaces and inheritance are used in open-source systems. Surveyed practitioners framed 'good design' in terms of impact on development and maintenance. Recognition of quality requires practitioner judgement (individually and as a group), and principles are valued over rules. Time constraints heighten sensitivity to the rework cost of poor design decisions. Examination of open source systems highlights the use of interface and inheritance. There is some evidence of 'textbook' use of these structures, and much use is simple. Outliers are widespread indicating a pragmatic approach. Design is found to reflect the pressures of practice - high-level decisions justify 'designed' structures and architecture, while uncertainty leads to deferred design decisions - simpler structures, repetition, and unconsolidated design. Sub-populations of structures can be identified which may represent common trade-offs. Useful insights are gained into practitioner attitude to design guidance. Patterns of use and structure are identified which may aid in assessment and comprehension of object oriented systems.This thesis investigates if object oriented guidance is relevant in practice, and how this affects software that is produced. This is achieved by surveying practitioners and studying how constructs such as interfaces and inheritance are used in open-source systems. Surveyed practitioners framed 'good design' in terms of impact on development and maintenance. Recognition of quality requires practitioner judgement (individually and as a group), and principles are valued over rules. Time constraints heighten sensitivity to the rework cost of poor design decisions. Examination of open source systems highlights the use of interface and inheritance. There is some evidence of 'textbook' use of these structures, and much use is simple. Outliers are widespread indicating a pragmatic approach. Design is found to reflect the pressures of practice - high-level decisions justify 'designed' structures and architecture, while uncertainty leads to deferred design decisions - simpler structures, repetition, and unconsolidated design. Sub-populations of structures can be identified which may represent common trade-offs. Useful insights are gained into practitioner attitude to design guidance. Patterns of use and structure are identified which may aid in assessment and comprehension of object oriented systems

Multi-paradigm modelling for cyber–physical systems: a descriptive framework

The complexity of cyber–physical systems (CPSS) is commonly addressed through complex workflows, involving models in a plethora of different formalisms, each with their own methods, techniques, and tools. Some workflow patterns, combined with particular types of formalisms and operations on models in these formalisms, are used successfully in engineering practice. To identify and reuse them, we refer to these combinations of workflow and formalism patterns as modelling paradigms. This paper proposes a unifying (Descriptive) Framework to describe these paradigms, as well as their combinations. This work is set in the context of Multi-Paradigm Modelling (MPM), which is based on the principle to model every part and aspect of a system explicitly, at the most appropriate level(s) of abstraction, using the most appropriate modelling formalism(s) and workflows. The purpose of the Descriptive Framework presented in this paper is to serve as a basis to reason about these formalisms, workflows, and their combinations. One crucial part of the framework is the ability to capture the structural essence of a paradigm through the concept of a paradigmatic structure. This is illustrated informally by means of two example paradigms commonly used in CPS: Discrete Event Dynamic Systems and Synchronous Data Flow. The presented framework also identifies the need to establish whether a paradigm candidate follows, or qualifies as, a (given) paradigm. To illustrate the ability of the framework to support combining paradigms, the paper shows examples of both workflow and formalism combinations. The presented framework is intended as a basis for characterisation and classification of paradigms, as a starting point for a rigorous formalisation of the framework (allowing formal analyses), and as a foundation for MPM tool development

Innovation strategies of energy firms

Investment by energy firms in innovation can have substantial economic and environmental impacts and benefits. Firms engage in innovation for different reasons. The main objective of this paper is to analyse the role that the different innovation objectives have on firms' decisions to invest in each of three types of innovation activity: namely, internal R&D, external R&D, and the acquisition of advanced machinery, equipment, or software. We consider four objectives: process innovation, product innovation, reducing environmental impact, and meeting regulatory requirements. With this approach, we examine how energy firms innovate to reduce their environmental impact in comparison with other innovation objectives. In carrying out the empirical analysis, we draw on data for private energy firms included in the Spanish Technological Innovation Panel for the period 2004-2016. In the empirical analysis, we take the potential persistence of innovation activities into account and we use multivariate probit models to control for possible complementarities between the different R&D and innovation investments. Our results show that internal and external R&D are undertaken to address environmental objectives and to meet regulatory requirements while the acquisition of advanced machinery has the purpose of developing process innovations

Relating fair testing and accordance for service replaceability

AbstractThe accordance pre-order describes whether a service can safely be replaced by another service. That is, all partners for the original service should be partners for the new service. Partners for a service interact with the service in such a way that always a certain common goal can be reached.We relate the accordance pre-order to the pre-orders known from the linear–branching time spectrum, notably fair testing. The differences between accordance and fair testing include the modeling of termination and success, and the parts of the services that cannot be used reliably by any partner. Apart from the theoretical results, we address the practical relevance of the introduced concepts

Pricing Capability and Its Strategic Dimensions

The notion of pricing as being of vital importance to firms is supported by a long line of publications that outline recommendations on how price should be managed in order to maximize long-term profits. This implies that pricing, or firm level pricing capability, should constitute an important area of research in the field of strategic management, a field which has as its prime objective to develop explanations of firm performance. Yet, research on pricing capability in strategic management has remained sparse. Rather than addressing this area directly, firm pricing capability has been treated as a non-strategic issue. This is done either by assuming that prices are automatically set at levels reflecting competitive market prices and the product’s value to customers, or by viewing price as an easily manageable part of the firm’s overall competitive strategy. This empirical study of pricing capability in five cases in the corrugated packaging industry illustrates the problems firms face when pricing their products. The study showed, not only that pricing was difficult to manage, but also that in order to handle the information and control-related uncertainties inherent in pricing decisions, the studied business units committed themselves to complex configurations of assets, routines, activities, and pricing policies. This thesis sets out to uncover the structure and strategic relevance of these configurations, and by doing so, to point out some fundamental problems in mainstream strategic management theory. As it turns out, the failure in addressing the strategic dimensions of pricing capability is not arbitrary, but reflects a theoretical gap that leaves established explanations of firm performance unable to account for important phenomena, such as pricing capability