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Thomas Erl

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Top Stories by Thomas Erl

One of the fundamental goals when designing service-oriented solutions is to attain a reduced degree of coupling between services, thereby increasing the freedom and flexibility with which services can be individually evolved. Achieving the right level of coupling "looseness" is most often considered a design issue that revolves around the service contract and the consumer programs that form dependencies upon it. However, for the service architect there are opportunities to establish intermediate layers of abstraction within the service implementation that further foster reduced levels of coupling between its internal moving parts so as to accommodate the evolution and governance of the service itself. These intermediate abstraction layers are created by the application of Service Façade, a design pattern focused on intra-service design. When designing a service, th... (more)

Book Excerpt: Fundamental Cloud Architectures

"This chapter is from the book, 'Cloud Computing: Concepts, Technology & Architecture' authored by Thomas Erl with Zaigham Mahmood and Ricardo Puttini, published by Pearson/Prentice Hall Professional, May 2013, ISBN 0133387526, Copyright 2013 Arcitura Education Inc. For more info please visit: http://www.informit.com/store/cloud-computing-concepts-technology-architecture-9780133387520" This chapter introduces and describes several of the more common foundational cloud architectural models, each exemplifying a common usage and characteristic of contemporary cloud-based environmen... (more)

A Look Ahead to the Service-Oriented World

BEA recently announced that it is broadening its SOA consulting practice, and that it has created a tool companies can use to learn about SOA and figure out how prepared they are to transition to the new architectural model. While BEA and other major vendors, such as IBM and Microsoft, continue to deepen their investments in SOA, many of us are still struggling to understand what SOA actually is. How well do you know SOA? If you were asked to write a definition right now, what would it be? One of the challenges has always been to distinguish SOA from a standard distributed archit... (more)

Paths to SOA

Many are comparing notes on two well-publicized paths to achieving SOA. The bottom-up approach is currently the most common variety, where Web services are created on an "as need" basis to fulfill mostly integration-related requirements. These services are typically application specific and simply re-create traditional integration channels over the open Web services communication framework. The top-down approach, on the other hand, is one of analysis, deep thought, and patience. Service-orientation is infused into the business process layer so that services can be modeled in ali... (more)

SOA Pattern of the Week (#2): Non-Agnostic Context

Should a service only be considered a service if it's reusable? The answer to this question, as asserted by this pattern, is a firm "no." While agnostic services (services providing multi-purpose logic with reuse potential, as per the Agnostic Context pattern), receive the most attention during service modeling and design phases, it can often be short-sighted to focus only on agnostic service logic. Non-agnostic logic represents any type of functionality that is unique to a given business process or task. In other words, non-agnostic logic is single-purpose in nature and therefo... (more)