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SOA & WOA: Article

Service-Oriented Architecture Best Practices

Meeting your goals takes a mixed effort

The concept of a service-oriented architecture is a powerful tool for simplifying enterprise integration. Following the three principles of modularity, encapsulation and loose coupling will achieve some amount of improvement for an individual service. It is insufficient to have a loose set of principles to guide enterprise architecture designs. It is also important to have "best practices" on how to build, run and manage enterprise systems. This document will cover the best practices that have been culled from Epiphany, a number of Epiphany's top customers and leading analyst firms.

Define the language of your enterprise. First and foremost, there must be a common language that your, enterprise must speak. This amounts to being able to define important entities as XML Schemas and transformations as XML style sheets. Enforcement is crucial, as well ensuring interoperability across an enterprise wide system. This is the single most important action an enterprise can take to smooth its transition to an SOA.

In one sense, this principle should not be necessary if industry standards groups could agree on basic XML document formats for simple things like names and addresses. Since this is unlikely to happen anytime soon, it is important that your organization set its own language policies now, and deal with transformation issues via XSLT later.

Establish a naming convention for your enterprise. In a SOA environment, having a document that formulates how to name Web services, service interfaces, legacy system endpoints, or any public component will help the enterprise architects, administrators, and developers provide consistent services.

Define service interfaces first, implement later. In a SOA, the interface for a Web service is more important than its actual implementation. When designing composite applications (i.e. applications composed from a cluster of web services), recognize that heterogeneity is the norm. One analyst study put the average number of hardware/software platforms in the Fortune 500 at 6. This underscores setting a baseline "language" for your organization, as heterogeneity is an unavoidable fact in any large enterprise.

In addition to having best practices around people, practices, and technology, it is also important to have "design patterns" that can be reused in order to make the design and construction of an SOA faster and easier. Just as there are design patterns for object-oriented programming, there is a group of experts who are looking at describing common enterprise workflows as a set of patterns. Led by BEA and the Middleware Company, initial work has been done to catalog a number of enterprise workflows captured as patterns for an SOA. While their efforts are in the early stage, the work appears promising.

Establish a service categorization. Services come in a number of flavors. An organization should decide on its services taxonomy. This definition will help to define development roles, as well as help to suggest a level or organizational structure. At a high level, there are only a few types of services. The Middleware Company group is attempting to pull together a set of best practices for building out a service-oriented architecture. The expert group has defined a taxonomy of services, which is a useful starting place:

  • Component services: Simple atomic services potentially acting on single enterprise resource (e.g., database, code, etc).
  • Data services: Service providing data querying, combination and transformation for multiple data sources.
  • Business services: Atomic services composed of combinations of component services and rules.
  • Workflow services: Long lived business processes coordinating other services with external interactions.
Separate rules. It is important to categorize business logic/rules, further, into "process" type business rules versus "UI" type business rules. Process-type business rules are good candidates to encompass within business services and UI-level business rules should be separated out.

Don't skimp on training. Start with a common skill set. Most organizations are new to the technologies behind SOA (like WS-I, WS-BPEL, etc.), so it is important for an IT staff to acquire the skills to understand and implement SOA on an enterprise-wide scale.

Architect a common management layer. A service-oriented architecture provides both additional opportunity and complexity for managing an operational system. Many of the infrastructure vendors like IBM and BEA provide the ability to monitor and manage Web services. It is important to implement a uniform management infrastructure for managing hardware, operating systems, applications, and Web services for maximum visibility.

Analyst firms have begun to discuss implementation issues around SOA as well. In a recent report, Forrester offers several suggestions for SOA best practices. The Forrester report offers several points for enterprises to consider:

Align services with business processes. This is important for a number of reasons. First, the service must be understood by the business users for it to be useful and successful. Second, the service should match the business process it is managing to mitigate the need to change management. Third, change management will be easier. As business processes change, determining which services need to change will be made easier.

Design decisions need to be made regarding integrating business rules within services. Consumer application-specific business rules may not have to be integrated within the producer services if there is no value in having these rules apply to other consumer applications. This also facilitates easy maintenance of services because there is less coordination with multiple consumer applications

Start with services, do Web services later. Moving to an SOA does not necessarily require Web services. Many companies have been successful building out an SOA message-oriented middleware (MOM). This includes JMS-based software as well as IBM WebSphere MQ (the former MQSeries). Applications rooted in MOM-based systems generally met the requirements of SOA: encapsulation, loose-coupling and modularity, but with the notion of messages on a queue rather than SOAP/XML messages.

Wrap packaged applications in service interfaces. This was mentioned above, but is important enough to restate. Enterprises should be wary of vendors claiming to provide a platform. Leveraging a single vendor's platform will unnecessarily tie an organization to one vendor. This is a risky strategy. It is better for enterprise information assets to speak a neutral, common language that will ensure interoperability.

Have a version resolution architecture. Web services present the ability to reuse software like never before. A Web service can be a public resource used by hundreds of applications. However, if the Web service changes the applications will have to change. This will create a maintenance nightmare. It is important to have an architecture where interfaces have a version associated with them, and a way of resolving a particular interface to a particular version. As Web service producers are changed, the consumers can be migrated slowly to the new service. This way disruption is minimized.

Conclusion
Successful enterprises know that achieving an organization's goals is a mix of best practices around people, policies, and technology. This article has attempted to illustrate that it is not sufficient to adopt SOA technologies. It is important to adopt best practices around how a group is organized and how it behaves. It is also important to adopt a set of policies that ensure smooth, visible operations and minimal effort in the face of change. This article has attempted show some of the current thinking around best practices from Epiphany, Epiphany's customers, and leading analyst firms. The nascent body of SOA best practices is still developing.

Resources

  • Some efforts in this area, like xNAL, are by no means universally accepted. See http://xml.coverpages.org/xnal.html for more details.
  • Gamma, E., et al. (1995). Design Patterns: Elements of Reusable Object-Oriented Softwar. Addison Wesley.
  • SOA Blueprints: www.middlewareresearch.com/soa-blueprints/
  • More Stories By Bill Roth

    Bill Roth is a Silicon Valley veteran with over 20 years in the industry. He has played numerous product marketing, product management and engineering roles at companies like BEA, Sun, Morgan Stanley, and EBay Enterprise. He was recently named one of the World's 30 Most Influential Cloud Bloggers.

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    Most Recent Comments
    David Knox 02/10/05 11:05:08 AM EST

    This arcticle starts off right with the three bastions of SOA (standardized interfaces, separation of concerns, loose coupling), after that it falls off the edge. I was most alarmed by the notion that SOA requires 'common language'. The author's argument clearly implies that an enterprise architecture must mandate an all XML protocol. I find it difficult to believe that J2EE app servers shouldn't freely use RMI-IIOP between containers. If every application in the enterprise must have the same transport protocol it contradicts the edict of loose coupling. In the first paragraph the author states a working SOA definition, in the second the author contradicts a necessary aspect of SOA.