The focus of this book is first and foremost on the design of services for SOA. There is a constant emphasis on how and where design principles can and should be applied with the ultimate SOA design patterns / Thomas Erl. — 1st ed. p. cm. compliance with the same contract design standards." Service Loose This principle preaches a “contract first” approach to service delivery . from Thomas Erl. Contents. mmoonneeyy.info 6/13/07 PM Page xiii. SOA: Principles of Service Design by Thomas Erl (mmoonneeyy.info).
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SOA Principles of Service Design. Home · SOA Principles Author: Thomas Erl Service-Oriented Modeling (SOA): Service Analysis, Design, and Architecture. —Farzin Yashar, IBM SOA Advanced Technologies “Thomas Erl's books service characteristics and service design principles for SOA from a. SOA: principles of service design / Thomas Erl. p. cm. ISBN ( hardback: alk. paper) 1. Web services. 2. Computer architecture. 3. System analysis.
The focus of this book is first and foremost on the design of services for SOA. Additional labels and Full description To Download Please Click http: What this translates into for the SOA professional is a need for an increased level of judgment. Service Composability Composition Member Design and Complex Compositions Service composition is a fundamental, yet potentially complex aspect of service-oriented design.
This supplies a common, real-world context to many of the topics explained in abstract. Up next are brief descriptions of what is covered in subsequent chapters.
Fundamentals Although this book is more about applying and realizing service-orientation than it is about understanding SOA basics, we do need to take the time to establish and define key concepts and fundamental terms.
These concepts and terms are used throughout the guide, and it is important that their meaning is always clear and consistent. The initial three chapters fulfill this requirement by providing concise introductory coverage.
How these chapters are organized is illustrated in Figure 1. Figure 1. Introduction Chapter 3: Collectively these goals provide strategic context for all chapters in Part II that document design principles. This chapter furthermore establishes the service-oriented computing platform by pro- viding definitions for the following terms: The chapter concludes with brief supple- mental coverage of additional SOA-related terms, concepts, and processes. Chapter 4: Service-Orientation This next chapter zooms in on the design paradigm that underlies service-oriented com- puting.
It begins with an overview of service-orientation by establishing its purpose and goals and then moves on to introduce its eight key design principles. How these princi- ples specifically relate to and support service-oriented architecture is also discussed. The manner in which the application of service-orientation changes the way solutions are delivered is explored next.
Pros and cons of previous approaches are documented and contrasted with the potential for service-orientation to improve upon them. Also explained are the challenges and impositions made by a transition toward this paradigm.
We move on to cover how the adoption of service-orientation transforms not only the technology and the design of an enterprise, but also the mindset and perception of solu- tion logic.
Because this paradigm is very much an evolutionary representation of IT, it is important to acknowledge its roots in past platforms and technology trends.
Chapter 5: Understanding Design Principles In preparation for Part II, this chapter provides a clear explanation of how subsequent chapters describe service-orientation principles within the context of SOA and service design, and how these principles may relate to design patterns.
Different types of prin- ciples are categorized, including a study of those that result in implemented design characteristics compared to those that tend to shape and moderate how others are applied. Additionally, four specific forms of contract granularity are established; subse- quent chapters then cover how principles affect these granularity types.
Chapter 5 concludes with a case study section that documents a business process for which services will be designed in subsequent chapters. Part II: Design Principles Service-orientation is a multi-dimensional subject matter. For example, there are guiding principles that each address a narrow aspect of service design and foster the creation of specific design characteristics.
Then there are the issues that arise from combining principles and seeking the right balance for each to be imple- mented to an appropriate extent. Part II consists of eight chapters—one for each service-orientation principle, as shown in Figure 1.
The chapters are structured with a baseline set of sections that are detailed in the Principle Profiles section of Chapter 5. Each chapter is further supplemented with a case study example that demonstrates the application of a principle within scenarios drawn from the background established in Chapter 2.
Introduction Figure 1. Collectively, these chapters provide a comprehensive documentation of the service-orientation paradigm. The following sections briefly introduce each chapter: Chapter 6: This chapter explains different types of required contract standardization and establishes common levels at which contracts can be harmonized.
Issues implicitly intro- duced by the use of service contracts, such as data models and policies, are discussed, and contracts are further architecturally positioned with an emphasis on Web services.
Chapter 7: Service Coupling Intra-Service and Consumer Dependencies Numerous types of coupling are explored, including the coupling of the service contract to underlying technology and implementation characteristics, as well as the coupling of the service consumers to the contract.
This chapter explores levels of attainable coupling and the implications of implementing more or less inter-service dependency. Addition- ally, the concept of design centralization is introduced as a means of supporting the real- ization of loose coupling in coordination with other principles.
Service Abstraction Information Hiding and Meta Abstraction Types The application of this principle determines how much of a service is revealed to the out- side world. Achieving a balanced level of abstraction can be one of the most difficult parts of service design.
Subsequent to describing the various forms and levels of abstrac- tion, this chapter discusses several associated design risks and the influence abstraction, as a design consideration, has on other principles.
Chapter 9: Service Reusability Commercial and Agnostic Design Increasing the value of solution logic by positioning services as reusable IT assets is a fundamental characteristic and objective of service-orientation.
This chapter provides a comprehensive profile of Service Reusability and its implications and extends into an exploration of service reuse levels and the specific influences raised by commercial design considerations. Planned versus actual reuse measuring is discussed, along with the risks and enterprise-wide effects of building and exposing agnostic service logic. Chapter Service Autonomy Processing Boundaries and Control The ability for a service to have control and governance over its execution environment is key for it to provide reliable, predictable runtime performance, a consideration especially important to the design of service compositions.
This chapter explores both runtime and design-time autonomy and provides measurable levels that define an extent of autonomy based on degrees of normalization and functional isolation. Service Statelessness State Management Deferral and Stateless Design Service designs capable of deferring state data and state management-related process- ing enable the implemented service to maximize its availability, an important quality especially in highly concurrent usage environments.
Provided in Chapter 11 is a detailed explanation of different types of state information and state management functions fol- lowed by levels of attainable service statelessness.
Service Discoverability Interpretability and Communication The opportunity for services to be utilized to their full potential can only be realized if their existence, purpose, and capabilities are either known or easily located and under- stood.
This chapter focuses on design characteristics associated with the discoverability and interpretability of services as they relate to the overall discovery aspect of service- oriented architecture. A checklist for measuring discoverability is provided, along with sections that document the risks and impacts of discoverability on service models and other principles. Introduction Chapter Service Composability Composition Member Design and Complex Compositions Service composition is a fundamental, yet potentially complex aspect of service-oriented design.
This principle deals with it head-on by establishing design requirements to ensure that services can effectively participate in larger composition configurations. Part III: Supplemental Chapter Service-Orientation and Object-Orientation: A Comparison of Principles and Concepts Object-oriented analysis and design OOAD is an established modeling and design par- adigm that has influenced numerous aspects of service-orientation.
This supplemental comparison is focused on concepts and principles only and is intended for those with an OOAD background. Supporting Practices This next chapter provides a set of supplementary practices and techniques for success- fully incorporating and applying service-orientation principles within the common IT enterprise.
Specifically, it discusses the use of service profile documents and associated vocabularies, along with common organizational roles. Mapping Service-Orientation Principles to Strategic Goals The book concludes with an exploration of how the eight service-orientation design principles individually relate to and support the strategic goals established in Chapter 3.
The content of this final chapter essentially establishes the strategic significance of each design principle. Appendices Appendix A: Case Study Conclusion The case study storyline is concluded here, as the original goals established in Chapter 2 are revisited and assessed against all that transpired in the subsequent case study examples. Process Descriptions Service-oriented analysis and design processes are illustrated and briefly described for reference purposes.
These processes are explained in detail in the book, Service-Oriented Architecture: Appendix C: Principles and Patterns Cross-Reference This last appendix is comprised of a list of design patterns referenced in this book. These patterns are documented separately in the book SOA: Design Patterns. How Color Is Used Symbols have distinct colors associated with them so that they are easily recognized within the different figures.
The one exception to this convention is when portions of a figure need to be highlighted for a particular reason. In this case, symbols may be col- ored red.
The conflict symbol which looks like a lightning bolt is always red because we usually need to highlight points of conflict. The Service Symbol When this book series began, I had already been part of numerous service modeling and design projects during which various tools were often awkwardly used to define serv- ices and inter-service relationships.
I found that it can be beneficial to visually distin- guish a technical service contract from other components and systems that also need to be modeled either as parts of the service or as parts of an enterprise environment that need to co-exist with services.
The base symbol I introduced to represent a service throughout the books in this series is a circle divided into two areas Figure 1. This symbol is by no means an indus- try standard convention. Background In plane geometry, a circle is a highly self-contained form. The use of this shape is appro- priate in that it reflects the levels of autonomy, independence, and individuality we seek to establish in every unit of logic we call a service. This service symbol was recently given an official name: This term is also inspired by plane geometry and provides an appropriate metaphor.
The symbol simply abstracts the official public technical contract details to establish an offi- cial service endpoint definition and to also represent interface details made available to the outside world.
Throughout this book, chorded circles express services with no hint of how the services are actually implemented. Different symbols are used to illustrate physical implemen- tation details of services as components and Web services. These symbols are explained in the symbol legend mentioned previously.
The Chorded Circle Is Complementary to UML As explained in Chapter 14, this symbol can be used on its own to represent abstract technical service contracts, it can be used in conjunction with traditional UML notation, or it does not need to be used at all.
Portions of UML can be adapted and used instead to express technical service contract details. The Chorded Circle Represents a Member of a Service Inventory What is most important about what this symbol visually communicates is that it repre- sents a unit of logic designed as a service. In other words, it is not used to represent just a Web service or a component, but an actual service shaped by service-orientation and part of a larger collective known as a service inventory as explained in Chapter 3.
It will therefore get you only so far within a service delivery lifecycle. Its pri- mary usage is during the service-oriented analysis process during which service mod- eling is carried out and service candidates are collaboratively defined and repeatedly refined by business and technology experts as part of a service inventory blueprint. The Chorded Circle Notation Is Extensible While the base version of this symbol provides only a simple, abstract expression of a service, extended versions can be created with more detail.
Additional labels and Introduction qualifiers are available to express further service characteristics, such as message exchange patterns, policy assertions, service models, implementation and encapsulation characteristics, and lifecycle status.
However, to keep things simple, these extensions are not used in this book. Service Design and Delivery. Principles of Inorganic Materials Design. Service Contracts Principles of European Law. Principles of Service Marketing and Management. Service Modelling: Principles and Applications. Principles of Modern Digital Design. Principles of Space Instrument Design.