Editorial Reviews. From the Back Cover. “SOA Design Patternsis an important contribution to eBook features: Highlight .. “WithSOA Design Patterns, Thomas Erl adds an indispensable SOA reference volume to the technologist's library. In cooperation with experts and practitioners throughout the SOA community, best-selling author Thomas Erl brings together the de facto catalog of design. Hardcover/Paperback: N/A; eBook: PDF ( page, MB); Language: English SOA Design Patterns by Thomas Erl with additional contributors;; SOA.
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Thomas Erl to explain some of the soa design patterns that address service contract design issues that occur both during the initial service design stage as. In this article we present 3 Inventory Governance Patterns from chapter 10 of the book SOA Design Patterns by Thomas Erl: Canonical. SOA Design Patterns (paperback) (The Prentice Hall Service Technology Series from Thomas Erl) (English Edition) eBook: Thomas Erl: ruthenpress.info: Kindle.
These candidates then form the basis of the physical service designs.
Architects and developers can now avoid irregularities and problematic characteristics within service contracts because they have gained control of the definition of these contracts. Project teams, especially in larger enterprises, run the constant risk of building functionality that already exists or is already in development, resulting in wasted effort, service logic redundancy, and service inventory denormalization.
Service metadata can be centrally published in a service registry so as to provide a formal means of service registration and discovery. A private service registry needs to be positioned as a central part of an inventory architecture supported by formal processes for registration and discovery. The service registry product needs to be adequately mature and reliable, and its required use and maintenance needs to be incorporated into all service delivery and governance processes and methodologies.
When growing a service inventory and fostering fundamental qualities such as those realized by Service Normalization and Logic Centralization , there is a constant risk of project teams inadvertently or sometimes even intentionally delivering new services or service capabilities that already exist or are already in development Figure All of these characteristics can undermine an SOA initiative by reducing its strategic benefit potential.
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. For more info please visit informit. Join a community of over , senior developers. View an example. You need to Register an InfoQ account or Login or login to post comments. But there's so much more behind being registered.
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Related Editorial. View an example Enter your e-mail address. Select your country Select a country I consent to InfoQ. The product summary doesn't mention that and I was a bit unhappy when I read on page 4 that many design patterns are "covered separately in SOA Principles of Service Design, a companion guide for this book.
I will try to write a real review when I get a chance. If you are assembling a SOA team of any size - one of the first immediate challenges is establishing clear communications. How to quickly and efficiently solve the challenge of adopting a set of common terms, a common lexicon for concepts, and a library of reusable architectural patterns?
SOA Design Patterns is an excellent reference for a team to adopt as an initial stake-in-the-ground. Later you can evolve your own library of patterns - extending upon this excellent body of work.
Much of this material will be known by some team members - but the thoroughness of the text provides a great level-set when assembling a team of mixed levels of experience. I particularly enjoyed Chapter Service Security Patterns and Chapter Service Interaction Security Patterns. It was for me a good bridge between security concepts I have applied in different areas such as PKI, Kerberos, etc. In addition to the two chapters dedicated to security, I also found the following sections interesting from a security perspective.
Chapter Atomic Transaction Services All tasks, or web services, within a transaction must be followed by an acknowledgement to indicate that the task completed.
If no such commit is received by task coordinator defined for the transaction, all the tasks within the transaction can be rolled back or other mitigating actions can take place. The web service specifications WS-Coordination and WS-Atomic Transactions can be utilized to employ this safer method of transaction management. Compensating Service Transaction This allows for a web service to have an "undo" event, defined at the task level, which can protect the encompassing transactions against individually failing web services.
These tasks can operate asynchronously, and the other inline web services are notified when an exception occurs so that they can handle the event appropriately without sacrificing the entire transaction. This helps build robust exception management and defend against resource starvation attacks. Reliable Messaging The method helps ensure message delivery. Reliable messaging can help protect against data integrity and service availability attacks.
Partial Validation At first this sounds like disabling some of the data validation performed by a web service, which is definitely discouraged remember, all input is evil , but instead what this does is use a language like XPath to filter out unnecessary data from a message so that only a subset of the data is validated; the omitted data is dropped off before the validation phase.
This can be used as an optimization technique. Service Callback This allows for asynchronous web service calls, which can be helpful for web services that can take a long time to process and respond. A callback address is provided so that the web service can be polled at intervals to see if it is ready to return data.
This can also be used to protect against resource starvation attacks. While the book is sometimes light on implementation details the author maintained platform agnosticism throughout it definitely provides a good starting point for managers, coders and architects by including sample SOAP headers, messages and WSDL definitions. What I also appreciated is that keywords are followed by the page number in parenthesis to easily look up the definition of that term.
Lastly, not only is the book filled with useful information, but the inside covers themselves is a pattern list reference. The book may be a challenge to read cover to cover, but is an excellent reference. It is a bookshelf staple for anyone implementing, or interested in, SOA.
Based on the positive reviews, I was hopeful that this book would provide lots of insight into practical approaches to designing and architecting SOA solutions. Unfortunately, I found it lacking. It seemed that many of the patterns were something like: New versions of your service have compatibility issues with old versions.
Make the new version more compatible. I'm sure there's lots of actually useful advice buried in here, but I was not patient enough to bother mining it. Ga naar site.