WebServices und serviceorientierte Architektur (German Edition)

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Service design specifies how the service can be described and therefore found, which business operations underlie the service function, which SOA design principles are supported and which technologies are needed to implement the service. Service design principles are embedded within the general principles of service-orientation that include: Service reuse[3,6,7], formal contract[3,8], lose coupling[2,3], abstrac- tion[3,7,9], composability[3,7], autonomy[3,7], statelessness[3,6], discoverability[10].

Mirbel, and R. Levina et al. This paper presents a generalized approach to service design that is based on exist- ing rules for service design and SOA design patterns. The suggested framework aims to support service design by providing a certain procedure and detailed activities in order to enhance the development procedure and to increase the probability for ser- vice reuse. The paper is structured as follows: First, the existing service development approaches and methodologies both in research and practice are reviewed.

The results of the analysis serve as basis for the development of a canonical framework for ser- vice design. Discussion of the results and outlook finish the paper. Their evaluation was not completely based on the method components suggested by [11], because not only service design meth- ods but also approaches explicitly situated in the SOA context were reviewed. Fur- ther criteria applied were completeness [11], i. There is little consensus on general service design principles in research and prac- tice. Though, the basic principles for service design can be considered as being: inter- face orientation, interoperability, modularization and process orientation, e.

Thus, the service design method or approach needs to include specification on inter- face design of a service. Besides the technical specification, meta-data on service content and use need to be specified.

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Communication aspects such as message for- mats, protocols and addresses need to be included as well as the effect of the service on data, process composition, security and further run-time aspects. Deployment of the interface design needs a service level agreement SLA as a realization of the abstraction principle of SOA, as well as its contents need to be included into service design approach. A further advantage lies in the changeability of the software ele- ments. Interoperability can be defined as the ability of software elements to exchange and interpret information with each other [13, 14].

Modularization implies composition of application systems or business processes into domains or services. Services are sup- posed to provide flexible support for business process automation. A service design approach or method need to provide guidelines for service granularity of data, busi- ness logic as well as functionality. In the following existing service design approaches or methods are evaluated refer- ring to the above mentioned criteria.

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It considers aspects of business engineering as well as technical aspects. Design and development of data models and interfaces are described as well as service design pattern are suggested. The service design takes all the basic SOA design principles such as autonomy, lose coupling, statelessness, etc. Though the approach is described as a methodology it does not offer a role specification for the design process. The aspect of service or- chestration is not further elaborated and service design is concentrated on a fine granular level.

Bottom- up as well as top-down ser- vice design patterns are conceptualized independently from their domain. This aspect supports a better service reuse and flexible service granu- larity. In software engineering the focus lies on component-based software development.

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CBSOSE offers an exhaus- tive documentation containing action description supported by examples and expected results. Service reuse is not explicitly considered. PMBSD provides a role model and generic description of the process activities and results. Business engineering is not considered in the methodology though a role model is given.

There are any tools specified that can support the methodology in service design. The design principles are not mentioned explicitly but reuse, interoperability and service orchestration are considered. Every phase of the method is supported by best practices. Executive's Guide to Service- Oriented Architecture EGSOA [7] approach includes bottom- up and top-down strat- egy for service identification using business services as well as legacy systems. The focus is on the business aspects of service development. There is no role model pre- sent in the method and no examples are provided.

The analysis and design phase sup- port the design principles such as SLA, interoperability, reuse, lose coupling and discoverability of the services. SOAM provides a clear process for service identification and system analysis on the business side, while SOAA provides comprehensive de- scription of technical service design. Basic steps of the service design process The abstract design process can be divided into four main phases: requirements analysis, identification of service operations, business design, and technical design see figure 1.

The process owner is involved into the process operation, business analyst is a member of a internal consulting team or a team that is concerned with business process management tools that are used e. IT developer transforms business requirements into software components. The first two phases are conducted by the process owner and business process analyst. The last two phases are completed by business process analysis and IT developer. It starts from the interoperability challenge in eGovernment and elaborates an approach to ease interoperability based on Semantic Web technologies.

The eGovernment domain is a large, heterogeneous, dynamic and shared information space with various semantic di erences of interpretation.

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This results in the challenge to achieve interoperability. Technical interoperability issues could mostly be overcome through standardization of protocols and technical interfaces cp. However, seman- tic interoperability is still a key obstacle for networked and thus integrated eGovernment processes due to di erent representations of data objects and interfaces. Therefore, con- cepts and technologies are required to express and handle the semantics of these entities. These characteristics encourage the application of Semantic Web concepts, that are based on formal modeling and description logics.

International research conferences re ect the potential for mutual gain in these domains, e. In order to demonstrate the interoperability challenge rising from process integration within the eGovernment domain, a cross-organizational scenario for the online application of a birth certi cate, as illustrated in gure 2. Taking into account the step-by-step digitalization of eGovernment processes the output of the birth certi cate application is still a paper-based document assuming the lack of an infrastructure for digital signatures.

The process includes a service for handling the payment of the birth certi cate fee, a resident registry service for checking the citizen input for consistence, a vital records o ce responsible for issuing the birth certi cate, and a statistical o ce to which the vital records o ce reports its activities. Usually, in order to ensure interoperability, eGovernment applications need to provide standard Web service interfaces including well-de ned message sets.

Indeed, in various countries national interoperability frameworks de ne XML schemes and Web service in- terfaces for exchanging data between administrations. An example for such a national e ort is the Danish eGovernment initiative, which focuses not only on the de nition but also on the reuse of base types and XML domain data structures[13]. In Germany due to its federal structure the approach is less centralized. But this initiative only ensures seamless interoperability within domain boundaries, e.

It has to be taken into account that in cross- organizational and cross-border eGovernment processes services of various public agen- cies from di erent domains and with di erent areas of operations are involved. In such scenarios the lack of cross-domain semantic interoperability results in enormous integra- tion e orts. Refering back to the given cross-organizational scenario gure 2. In one domain Name and Address might be di erent entities and Name might be a complex type consisting of di erent attributes for Given Name and Surname, while an Address might be a complex type consisting of attributes such as Street, Street Number, etc.

In the other domain standard a concept for an address named PostalAddress might be modeled as a complex type that contains just one single attribute all together instead of Street and Street Number. FullName might be modeled similar. Moreover, ZIP from the vital records o ce and PostalCode from the statistical o ce might represent the same concept of a zip code but are represented as di erent XML schema types. It is a fact that most eGovernment data exchange standards are being developed inde- pendently from each other and that in di erent eGovernment application domains the requirements for information granularity di er signi cantly.

Therefore, it is not feasible to address this problem by introducing a global ontology or a global schema. In order to serve best for intra-domain integration, domain standards need to evolve independently from each other. Chapter 4 refers back to this scenario gure 2. In recent years the focus on multi-layered governance processes has gained popularity in political science as an alternative to traditional isolated government analysis.

In consideration of globalization and technological progress governance describes the growing involvement of non-state actors in collective problem-solving at all levels from local to global, addressing the three main functions of collective problem-solving, i. The focus is put on the various interactions in networked governance processes and how they contribute to achieve public interest objectives. The same terminology follows the shift from eGovernment to eGovernance, where the impact of ICT in these networked governance processes is addressed.

Hence, the role of process integration and interoper- ability becomes a central issue. However, there is not yet a common conceptualization of eGovernance [17] and sometimes the term is misused for describing the governance of ICT infrastructure. Nevertheless, eGovernance can be a crucial part in enhancing governance. Especially with regard to global governance - where no government exists - virtual collaboration, much easier to achieve and to maintain than traditional collab- oration, can contribute to link the various actors targeting the challenges globalization raises[18].

This chapter gives background information on how the challenges in process integration discussed in chapter 1 and chapter 2 can be addressed. The interoperability challenge is analysed and related to the goals of this thesis. Technologies for achieving interoper- ability are presented, including Web services, Web service composition, Semantic Web services and semantic information integration approaches.

Finally, related work is pre- sented for both the composition aspect of this work and the resulting ontology mediation aspect. In the context of the European Union's Information Society activities interoperability is de ned as the means by which the inter-linking of systems, information and ways of working, whether within or between administrations, nationally or across Europe, or with the enterprise sector, occurs[19]. Furthermore, it says that interoperability is the chain that allows information and computer systems to be joined up both within organisations and then across organisational boundaries with other organisations, administrations, enterprises or citizens.

Interoperability has three aspects[19]:. While the requirement for interoperability seems obvious, it is a fact that information systems today are not interoperable in the way that eGovernment process integration can be realized to its full potential. In the context of process integration the recent development of Web service standards [2], which are discussed in more detail in the next section 3.

In order to enable ICT applications to exchange and combine information and accordingly process it in a meaningful manner, it requires agreement on more complex issues such as the relation to the context within information is created and used. This is what semantic interoperability is about. It involves agreement on how to represent and give context to information in order to exchange it.

Semantic interoperability is a core requirement for distributed information systems to share and process information, even when they have been designed independently. As this work focuses on semantic interoperability the subsequent sections concentrate on technologies and concepts which are exploited to achieve technical interoperability, which is a foundation for semantic interoperability on the one hand and technologies and concepts for accomplishing semantic interoperability itself on the other hand.

In chapter 7 this work will also touch the aspect of organizational interoperability and outline in how far the presented approach raises requirements for organizational measures. Web service standards are the foundation for technical interoperability in process integration. The W3C de nes Web services as programmatic interfaces for application to application communication over the World Wide Web[2].

Web services feature the following characteristics[20]:. The idea behind Web services is not new. Within this context in recent years a couple of Web service standards have emerged. The base speci cations are:. Standards for non-functional properties such as transaction support[23]or security and encryption issues[24]are evolving. Web services are mostly applied as an instantiation of a service oriented architecture SOA. Thereby, ICT systems supporting business processes are split of into a set of loosely coupled reusable services, where each service realizes one modular unit of busi- ness logic.

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Due to standardization Web services can be implemented independent from any platform and programming language. Subsequently, ICT applications that support business processes can be exibly realized as a composition of several services together realizing the business goal. The targeted exibility is ensured based on the characteristics of Web services described above. SOA promises to allow exible application integration and adaptation on changing business processes and thus has received much interest to support business-to-business applications or enterprise application integration EAI.

The design process of such service compositions is also called programming in the large and their execution is refered to as Web service orchestration. In order to keep the composition independent from the underlying ICT infrastructure, the exact data ow and control ow is provided in a composition language, which can be interpreted by work ow execution engines. Di erent approaches for such languages have arisen, e. BPEL 1 de nes a business process as an XML-serialized description of data ow and control ow between participating Web services and allows to run the process in a long-running asynchronous manner.

In order to ease the design of service compositions in BPEL, vendors o er a range of graphical integrated development environments as illustrated in gure. However, the composition design is still complex and time-consuming cp. Thus, the implicit semantics of services can only be understood by a human composer. The lack of explicit semantics in Web service descriptions is an obstacle in increasing automatization and further tool support in the process of composition design[29].

In consideration of the before discussed shortcomings the idea of bringing implicit ser- vice semantics to an explicit level has arisen. By providing machine understandable Web service descriptions with formally de ned semantics powerful inference engines and matchmaking mechanisms could be enabled, in order to automate the whole composition process including discovery, composition, execution and interoperation of Web services.

The concepts and technologies for expressing explicit service semantics are based on Semantic Web research.

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The Semantic Web is an extension to the current World Wide Web by enriching its content with machine processable meaning or semantics. In order to enable machines to process Web content with regard to its meaning, the content needs to be expressed in a machine understandable ontology. Whereas ontology means a formal and explicit speci cation of a shared conceptualization of a domain[30].


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The formal and explicit manner ensures that the so modelled meaning can be processed by machines and the shared aspect ensures a commonly accepted understanding, so that the modelled meaning can be processed the same way anywhere. In more detail an ontology consists of the following elements:. Some traditional approaches regard rules separate from ontologies. But since the mathe- matical formalization of ontologies in terms of description logics, this distinction becomes obsolete and rules become an essential part of domain conceptualizations.

Description logics are a subset of predicate logic. The ontology elements discussed before are repre- sented as predicates 4 and logic operators within formulas. Description logics are aimed at being tractable on the one hand but keeping a high degree of semantic expressiveness on the other hand.

Therefore, description logics are designed to be decidable in con- trast to predicate logic, that is undecidable [31]. Thus, knowledge modelling gets a solid mathematical foundation. Subsequently, this formalism enables machines to interpret or reason over knowledge representations.

However, there is a trade-o between semantic expressiveness and computational complexity of reasoning and thus many di erent vari- ants of description logics have emerged [34]. Having modelled content in that manner knowledge based systems using inference engines and reasoners as illustrated in gure. Figure 3. The vision of the Semantic Web is about applying these concepts to the World Wide Web and using it as a huge knowledge base enabling powerful knowledge based applica- tions.

Consequently, reasoning has to be realized on a partial and incomplete knowledge base. This background has yifield to the concept of open-world semantics in contrast to closed-world semantics used in the context described before. The concept of open-world semantics assumes that the absence of information about a fact does not indicate that this fact is false. Hence, it is possible to reason over a dynamic knowledge base without generating contradictions.

The W3C has released several standards to realize the Semantic Web vision as illustrated in gure 3. The foundation is build by means of a standardized encoding of data Unicode , which joins di erent character sets to one international character set together with the Unified. XML enables the structuring of data through opening and closing tags, which eases the structured processing by parsers.

Tag names can be speci ed in di erent namespaces. NS to avoid name collisions. XML schema allows to specify grammars to de ne how the di erent tags can be structured. These statements also called triples consist of subject, predicate, and object. A set of statements spans a graph, which is also referred to as the RDF-Graph. Conceptually RDF is based on the semantic relational data model[56].

For example, it can be stated that Nils is the author of this thesis. All important resources in the Web should be identi ed by an URI, so that statements can refer to it. Objects can also be empty nodes or literals. Furthermore, predicates are de ned in vocabularies, which are referred to by namespaces.

These vocabularies are speci ed in RDF Schema, which is similar to an ontology de nition language but less expressive and less formalized. For example, RDF Schema allows to de ne classes in terms of using inheritance and properties speci ed with their domain and range. The speci cation of RDF Schema is given in[35].

The ontology layer is based on the RDF layer. The layers discussed so far represent the current state of the Semantic Web research that has reached a clear conceptualization, whether the upper layers represent the future requirements for the Semantic Web and are much more under construction.

Besides the logic layer, which is discussed below, the far reaching vision is to enable heuristic engines which can proof whether a statement is correct or wrong based on ontologies and rules queried from the Semantic Web. Furthermore, it is aspired to create a Semantic Web of Trust based on authentication mechanisms including digital signatures and trust relations.

However, currently the main debate is focused on the logic layer and how to integrate rules to make OWL more expressive. In that context a debate has arisen, whether this extension by rules should be realized by means of splitting the Semantic Web stack with rules and OWL ontologies sitting side by side on the same level on top of an extra intermediate layer.

The purpose is to allow closed-world semantics as an alternative to open-world semantics exposed by OWL. A computer node once buffers performed Service Views Service Views and forms for over a defined period this service call with the result, which is referred to below as service or service-mimicry. When service mimicry of service emulated by caching the input-output tuple of a web service call.

For the stored views of mimicry host acts like the original service. This method is particularly suitable for dynamic networks with ad hoc character, since such a connected computer can replicate through the mimicry the service of the original for a defined period. Der Dienst wird mit Eingabe Input aufgerufen. The service is called with input input. The return is also obtained the time of first call of the service next to the actual result Result. Dieser Zeitpunkt kann sowohl durch den Serviceprovider selbst als auch durch den Aufrufer in seiner Mimikry-Funktion bereitgestellt werden.

This time can be provided in his mimicry function both by the service provider itself or by the caller. By the tuple Service 1st Service Call can be ensured uniqueness of the service in combination with the initial Serviceerbringer. Each service, 1st Service Call service saves both call parameters and results in the form of Input Output tuples. For the so-cached results of mimicry host can a service with the same functional property such. Mimicry hosts can not both active and passive act.

Common to both modes is that if a mimicry host not just mimicry host any durchfuhrt a service call to another host, he offers this call as mimicry service. Besteht zwischen zwei Mimikry-Hosts eine Netzwerkverbindung, dann synchronisieren sie ihre aktuellen Mimikry-Dienste Tupel und Beschreibungen , was auch Aktives Agieren eines Mimikry-Host genannt wird. When two mimicry hosts a network connection, they synchronize their current mimicry services tuples and descriptions , which is also called active act of mimicry host.


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  • Service calls are established as mimicry service only asked him in the passive mode of mimicry hosts. Hosts both expression can operate in a network respectively. As with conventional proxies also the permanent timeliness of the results can not be guaranteed by the service mimicry process. Both temporal variation and by changing the position returned results may vary in quality.

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    Auch mit nicht permanenten Netzwerkverbindungen zwischen einzelnen Rechnerknoten in dynamischen ad-hoc peer-to-peer Netzwerken, die aber eine Architektur mit SOA-artigem Charakter realisieren sollen, soll ein lokaler Teilnehmer Client idealerweise alle Dienste im Netz sehen, auch wenn diese aktuell nicht erreichbar sind.

    Even with non-permanent network connections between individual computer nodes in dynamic ad hoc peer-to-peer networks, but should implement an architecture with SOA-like character, a local participant client should ideally see all services on the network, even if they currently are unreachable.

    The invention is further illustrated by the figures illustrated in the following embodiments. Es zeigen: Show it:. A sequence diagram of a further part of the method for replicating a service external server is not available, access to mimicry service to drop to Q. A method for caching of signature and earnings of called service calls described. In the present case, the address of the external server ES service address is returned by the directory VE. The mimicry server MI now starts on the network an inquiry request x, y, z with the external server ES and gets the result result R back.

    After the return of result R to the client CL, the tuple of the parameters and of the result is x, y, z, R stored in the server MI mimicry.

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