International Sales [email protected] Library of Congress Cataloging- in-Publication Data: Erl, Thomas. SOA design patterns / Thomas Erl. — 1st ed. “Erl's SOA Design Patterns is for the IT decision maker determined to ing of the SOA Design Patterns book Thomas Erl has shown his real. In this article we present 3 Inventory Governance Patterns from chapter 10 of the book SOA Design Patterns by Thomas Erl: Canonical.
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Author: Thomas Erl SOA Design Patterns · Read more · Applied SOA: Service- Oriented Architecture and Design Strategies. Read more. As an architectural pattern, SOA is an appropriate solution in some situations; . The book SOA Design Patterns by Thomas Erl (with contributions from over thirty .com/us/technologies/soa/oracle-soa-governance-best-practicepdf. Thomas Erl. PRENTICE HALL .. Web services and the service-oriented architecture (SOA) 48 .. Streamlining the service design with usage patterns .. for published output, such as a PDF document.
References 1. Arsanjani, A.
Engels, G. Erradi, A. In: Proc. IEEE Int. Erl, T. Feuerlicht, G. Fielding, R.
PhD Theses. University of California, Irvine Google Scholar 8. Fronckowiak, J. Heineman, G. Addison-Wesley, Boston Google Scholar Kaabi, R. A service registry is established as a central part of the surrounding infrastructure and is used by service owners and designers to:. As emphasized in discovery-related governance patterns, the registration process requires that discovery information be recorded in a highly descriptive and communicative manner so that it can be used by project teams to:.
By providing a current and well-maintained registry of service contexts and capabilities, effective service discovery can be achieved Figure Note - Metadata Centralization is clearly a design pattern associated with the Service Discoverability design principle and the discovery of services in general.
Why then is it not simply called Service Discovery? Service discovery itself is a process that is carried out once an enterprise has successfully applied Metadata Centralization to its architecture and the Service Discoverability design principle to its services. The process of service discovery is therefore related to a set of SOA governance patterns documented separately in the upcoming title SOA Governance that will be released as part of this book series.
Finally, formal processes for the registration and discovery of services and capabilities need to be established. Note - This pattern can be applied to a single service inventory or multiple domain inventories, depending on the ability of the service registry product to associate domains with service profile records.
For a service profile template and descriptions of service discovery and interpretation processes, see Chapters 16 and 12, respectively, in SOA Principles of Service Design. Service registration and discovery processes are key success factors for the effective governance of a service inventory.
If the processes are not respected or followed consistently by project teams or if the registry is not kept current, then the value potential of Metadata Centralization will severely diminish.
From a design perspective, however, this pattern will introduce the need for metadata standardization, as per the Service Discoverability principle. It will further require that metadata documentation and registration become part of the standard service delivery lifecycles.
There may further be a need to create a new organizational role in support of realizing Metadata Centralization. A person or a group would act as service registry custodian and assume responsibility for collecting the required metadata and maintaining the registry.
Metadata Centralization essentially establishes a service registry, which is key to ensuring the long-term successful application of Logic Centralization and Contract Centralization If the correct services and their contracts can be effectively located discovered , then the risk of inadvertently introducing redundant logic into an environment is reduced, further supporting Service Normalization Agnostic services represent the primary type of service for which metadata needs to be centralized for discovery purposes, which is why this pattern is especially relevant to services defined as a result of Entity Abstraction and Utility Abstraction As explained in the Logic Centralization example from Chapter 6, the original functional overlap between the Alleywood Areas and Region services could have gone undetected, resulting in the quality and integrity of the service inventory being negatively affected.
For this reason, it was determined early on that a service registry would be required to support Service Normalization and ensure the consistent application of Logic Centralization However, due to the decision to establish separate domain service inventories, architects struggle with the option of implementing a separate service registry for each inventory. Although it would continue to allow each group to govern their respective service collection independently, it would establish two different repositories.
It is anticipated that Alleywood and Tri-Fold services will need to interoperate.
Those creating cross-inventory compositions will therefore need to issue separate queries in order to discover the required service capabilities. The awkwardness of this governance architecture eventually prompts McPherson to establish a central enterprise service registry instead Figure Service contracts within the same service inventory that are versioned differently will cause numerous interoperability and governance problems. Service contract versioning rules and the expression of version information are standardized within a service inventory boundary.
Governance and design standards are required to ensure consistent versioning of service contracts within the inventory boundary. The creation and enforcement of the required versioning standards introduce new governance demands. When service contracts within the same service inventory are subjected to different versioning approaches and conventions, post-implementation contract-level disparity emerges, compromising interoperability and effective service governance Figure This can negatively impact design-time consumer development, runtime service access, service reusability, and the overall evolution of the service inventory as a whole.
Service contracts within the same inventory are versioned according to the same conventions and as part of the same overall versioning strategy Figure This ensures a consistent governance path for each service, thereby preserving contract standardization and intra-inventory compatibility and interoperability. This pattern generally requires that a single versioning strategy be chosen, comprised of a series of rules and conventions that essentially become governance standards.
There is the constant risk that project teams will continue to use their own versioning approaches, or rely too heavily on patterns like Concurrent Contracts , which allows them to simply add new contracts to an existing service.
The successful application of any versioning strategy will require strong support for the adherence to its rules and conventions to the extent that the chosen versioning approach becomes an inventory-wide standard on par with any other design standard.
This introduces the need for a new organizational role that is tasked with enforcing the processes and syntactical characteristics that are defined as part of the strategy.
Canonical Versioning essentially formalizes the application of Compatible Change , Version Identification , and Termination Notification , in that the overarching strategy established by this pattern will determine how and to what extent each of these more specific versioning patterns is applied.
The application of Metadata Centralization results in a service registry that enables effective discovery of different contract versions and Canonical Expression implements characteristics in service contracts that improve their legibility.
Both of these patterns therefore aid the goals of Canonical Versioning. Note - Before continuing with this case study example, be sure to read up on the Policy Check service that was defined in the State Repository case study example and then later positioned to support multiple inventories as part of the example for Cross-Domain Utility Layer The FRC announced that due to new government legislation, it has revised some of its policies.
This changes the policy data that was being made available electronically via its public Web services. The Alleywood Policy Check service was originally positioned to shield the rest of the Alleywood service inventory from these types of changes by providing the sole access point for FRC policy data.
Although its service logic can be augmented to accommodate changes to the FRC services, architects soon realize that they cannot prevent having to issue a new version of the Policy Check contract because the FRC has added new content and structure into their policy schemas. After some research into common versioning practices and further deliberation, they produce a versioning strategy comprised of a set of specific conventions and rules:.
The previously described scenario results in a set of incompatible changes that requires that the major version number of the Policy Check service contract be incremented from 1.
Example The Alleywood architects acknowledge that defining the versioning approach is only the first step. In order for Canonical Versioning to be fully realized, these new rules and standards must be applied to any future service contracts that need to be versioned. This leads to the creation of a new process that is placed under the jurisdiction of the governance group. SOA-based systems can therefore function independently of development technologies and platforms such as Java,.
NET, etc. Services written in C running on. NET platforms and services written in Java running on Java EE platforms, for example, can both be consumed by a common composite application or client. Applications running on either platform can also consume services running on the other as web services that facilitate reuse. Service-oriented modeling is an SOA framework that identifies the various disciplines that guide SOA practitioners to conceptualize, analyze, design, and architect their service-oriented assets.
The Service-oriented modeling framework SOMF offers a modeling language and a work structure or "map" depicting the various components that contribute to a successful service-oriented modeling approach. It illustrates the major elements that identify the "what to do" aspects of a service development scheme.
The model enables practitioners to craft a project plan and to identify the milestones of a service-oriented initiative. SOMF also provides a common modeling notation to address alignment between business and IT organizations.
It can also simplify interconnection to—and usage of—existing IT legacy assets. With SOA, the idea is that an organization can look at a problem holistically.
A business has more overall control. Theoretically there would not be a mass of developers using whatever tool sets might please them. But rather they would be coding to a standard that is set within the business.
They can also develop enterprise-wide SOA that encapsulates a business-oriented infrastructure. SOA has also been illustrated as a highway system providing efficiency for car drivers. The point being that if everyone had a car, but there was no highway anywhere, things would be limited and disorganized, in any attempt to get anywhere quickly or efficiently. It captures many of the best practices of previous software architectures. In communications systems, for example, little development of solutions that use truly static bindings to talk to other equipment in the network has taken place.