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2004 | Buch

Distributed Information Systems Kapitel lesen Erstes Kapitel lesen

Web Services

Concepts, Architectures and Applications

verfasst von: Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju

Verlag: Springer Berlin Heidelberg

Buchreihe : Data-Centric Systems and Applications

Enthalten in: Professional Book Archive

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Über dieses Buch

Like many other incipient technologies, Web services are still surrounded by a tremendous level of noise. This noise results from the always dangerous combination of wishful thinking on the part of research and industry and of a lack of clear understanding of how Web services came to be. On the one hand, multiple contradictory interpretations are created by the many attempts to realign existing technology and strategies with Web services. On the other hand, the emphasis on what could be done with Web services in the future often makes us lose track of what can be really done with Web services today and in the short term. These factors make it extremely difficult to get a coherent picture of what Web services are, what they contribute, and where they will be applied.

Alonso and his co-authors deliberately take a step back. Based on their academic and industrial experience with middleware and enterprise application integration systems, they describe the fundamental concepts behind the notion of Web services and present them as the natural evolution of conventional middleware, necessary to meet the challenges of the Web and of B2B application integration.

Rather than providing a reference guide or a "how to write your first Web service" kind of book, they discuss the main objectives of Web services, the challenges that must be faced to achieve them, and the opportunities that this novel technology provides. Established, as well as recently proposed, standards and techniques (e.g., WSDL, UDDI, SOAP, WS-Coordination, WS-Transactions, and BPEL), are then examined in the context of this discussion in order to emphasize their scope, benefits, and shortcomings. Thus, the book is ideally suited both for professionals considering the development of application integration solutions and for research and students interesting in understanding and contributing to the evolution of enterprise application technologies.

Inhaltsverzeichnis

Frontmatter

Conventional Middleware

Frontmatter
1. Distributed Information Systems
Abstract
Web services are a form of distributed information system. Many of the problems that Web services try to solve, as well as the design constraints encountered along the way, can be understood by considering how distributed information systems evolved in the past. As part of this evolution process, a key aspect to keep in mind is that while the technology has changed, the problems that need to be solved are to a large extent the same. Thus, the first step toward looking at Web services from the correct perspective is to develop a comprehensive understanding of distributed information systems.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
2. Middleware
Abstract
Middleware facilitates and manages the interaction between applications across heterogeneous computing platforms. It is the architectural solution to the problem of integrating a collection of servers and applications under a common service interface. Simple as this description is, it still covers a wide range of situations. Obviously, integrating two databases residing on the same LAN is not the same as integrating two complete 3-tier systems residing on different branches of the same company and linked through a leased line. For the same reason, the solutions employed in the latter case cannot be the same if the systems to be integrated are owned by different companies and must communicate through the Internet.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
3. Enterprise Application Integration
Abstract
Middleware and enterprise application integration (EAI) are not completely orthogonal concepts. They are, however, distinct enough to warrant separate treatment. As we saw in Chapter 2, middleware constitutes the basic infrastructure behind any distributed information system. Initially, middleware was used to construct new systems and to link to mainframe-based systems (2-tier architectures). Later, it was used to distribute the application logic and to integrate the many servers created by 3-tier architectures.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
4. Web Technologies
Abstract
In Chapter 3, we have studied the need for integrating enterprise applications in order to achieve business process automation. The need to integrate, however, is not limited to the systems within a single company. The same advantages that can be derived from automating a company’s business processes can be obtained from automating business processes encompassing several companies. Hence, it should not come as a surprise that there is as much interest in inter-enterprise application integration as there is in intra-enterprise application integration. This chapter serves as a transition between the chapters that precede, which focus on intra-enterprise application integration and on middleware services, and the chapters that follow, which describe Web services for inter-enterprise application integration. The purpose of this chapter is to introduce the basic Web technologies that are used to implement the “Web” portion of Web services.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju

Web Services

Frontmatter
5. Web Services
Abstract
In previous chapters we have discussed the architecture of information systems (Chapter 1), middleware and enterprise application integration (Chapters 2 and 3), and the basics of Web technology (Chapter 4). These chapters have shown a chronological evolution of the technology used for EAI and for building distributed applications. All these technologies have been rather successful in addressing several of the problems created by application integration. The success, however, has been restricted to certain settings (e.g., LAN-based systems, homogeneous middleware platforms, etc.). True application integration requires tools that go one step beyond what conventional middleware and EAI platforms have achieved. Web services and the associated technology are being leveraged to take such a step.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
6. Basic Web Services Technology
Abstract
Many Web services architectures today are based on three components: the service requester, the service provider, and the service registry, thereby closely following a client/server model with an explicit name and directory service (the service registry). Albeit simple, such an architecture illustrates quite well the basic infrastructure necessary to implement Web services: a way to communicate (SOAP), a way to describe services (WSDL), and a name and directory server (UDDI). SOAP, WSDL and UDDI are nowadays the core of Web services. Specifications covering other aspects are typically designed based on SOAP, WSDL and UDDI. This is similar to the way conventional middleware platforms are built, where the basic components are interaction protocols, IDLs, and name and directory services.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
7. Service coordination protocols
Abstract
The basic Web services infrastructure presented in the previous chapter suffices to implement simple interactions. In particular, it supports interactions where the client invokes a single operation on a Web service. When the interaction involves coordinated sequences of operations, additional abstractions and tools are needed to ensure the correctness and consistency of the interactions. This is no different from how conventional middleware evolved. RPCs support simple, one-call-at-a-time interactions between clients and servers. Adding guarantees to the interactions (e.g., transactions), requires additional protocols (e.g. two-phase commit) and an infrastructure that supports the necessary abstractions and the corresponding protocols (e.g., a TP monitor). The same applies to Web services. Once we go beyond simple, independent service invocations, new protocols, abstractions, and infrastructures are needed.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
8. Service Composition
Abstract
The previous chapter has shown that interactions among Web services can consist of several operation invocations, to be executed in accordance with certain ordering constraints. We have discussed one of two implications of that observation: the need for coordination protocols and for middleware that helps define and enforce protocols. This chapter tackles the other implication, which is related to the implementation of Web services whose business logic involves the invocation of operations offered by other Web services. We refer to a service implemented by combining the functionality provided by other Web services as a composite service, and the process of developing a composite Web service as service composition.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
9. Outlook
Abstract
Throughout this book we have tried to balance two conflicting perspectives. One sees Web services as a revolutionary technology triggering radical changes in the way we think about middleware, application integration, or the way we use the Internet. The other sees Web services as yet another step in the evolution of middleware and EAI. In the revolutionary camp, the assumption seems to be that once applications speak XML, systems support SOAP, and providers describe services using WSDL and advertise them in UDDI registries, then Web services will facilitate the development of infrastructures that support programmatic application integration, dynamic B2B marketplaces, and the seamless integration of IT infrastructures from different corporations. In the evolutionary side, Web services are just an additional layer on top of existing middleware and EAI platforms that provides a set of simple, lowest common denominator interfaces for interactions across the Internet.
Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju
Backmatter
Metadaten
Titel
Web Services
verfasst von
Gustavo Alonso
Fabio Casati
Harumi Kuno
Vijay Machiraju
Copyright-Jahr
2004
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-662-10876-5
Print ISBN
978-3-642-07888-0
DOI
https://doi.org/10.1007/978-3-662-10876-5