Leverage the Service Refactoring Pattern

September 6, 2010

The Service Refactoring pattern facilitates changes in service logic and/or underlying service implementation while preserving existing consumer contracts.

The Service Refactoring pattern allows the service provider to change the service implementation while preserving existing service contracts. This allows the provider the flexibility to honor existing consumers while taking advantage of streamlined service logic and/or better technologies. If this idea sounds familiar, it is based on the refactoring principles and techniques advocated by Martin Fowler in the object oriented design paradigm and aims to achieve the same result for services in a SOA context. This pattern requires the development of an adapter – that will translate messages conforming to the existing contract into the refactored contract and vice versa.

This pattern:

  • Allows for phased migration of consumers who use existing contract to a new one
  • Allows the provider to upgrade/enhance service behavior in phases. The refactoring can be accomplished via multiple steps and don’t all have to be bundled in a single release
  • Eliminates the need for consumers to change code to take advantage of refactored service
  • Allows new consumers to bind to the enhanced service contract and allows for new and existing consumers to co-exist
  • Potentially enhance performance, availability, and scalability as new consumers come on board

There is a need for strong and coordinated service governance to make sure that consumers are aware of the refactoring effort, retest to validate the behavior, and ultimately provide sign-off for the service capability to be turned on in a production environment. At a minimum, this pattern needs to make sure that existing consumers conduct regression testing to guarantee that the refactored service doesn’t necessitate code changes.


Using Design Patterns To Build Reusable Assets

October 2, 2009

Design patterns are common solutions to design problems based on a given context. When used appropriately, they help address changing requirements. There are several books on design patterns and I don’t want to repeat that information here. Instead, we will look at design patterns in the context of building and integrating reusable assets. Here is a starter list:

  • Strategy – Polymorphically bind concrete implementations to execute a flavor of logic. This is useful when encapsulating product variations. If you need to support multiple flavors of a feature at runtime it is applicable. For instance, searching a product catalog feature could use exact text matching for product A while using fuzzy matching for product B. This could also be used to support multiple flavors within the same product and choosing a concrete implementation based on criteria. For this feature, it could be type of user or the nature of input parameter or volume of potential results.
  • Adapter – Used for translating one interface from another in order to integrate incompatible interfaces. This is useful in a couple of situations. Introduce an adapter when reusing a legacy asset. It is also useful when there are multiple versions of a reusable asset that you need to support in production. A single implementation can be reused to support the new version and the old version. The old version of the asset can be wrapped by an adapter for backward compatibility.
  • Template method – Used to define a generic set of steps to execute with placeholders for concrete steps that need customization. I tend to use this pattern for reusing business process flows across varying product types. It can also be used when implementing a standard request processing flow for both library components and web services. This is a common pattern when introducing horizontal concerns (such as security, logging, auditing etc.) as part of the processing algorithm.
  • Abstract factory – Used to build a family of products that need to be created as a cohesive unit. You also don’t want your calling code to know the nuances and complexity of constructing domain objects. This pattern is very useful when creating domain objects that require business rules and you want the complex creation in a single place in your codebase. I typically use this pattern with supporting bundling of product features. If you want to reuse a set of product features across bundles you will have several objects that all need to be carefully chosen at runtime for consistent behavior.
  • Decorator – Used with a core capability that you want to augment at runtime. Decorators are pluggable components that can be attached or detached at runtime. The upside is that the decorators and the component being decorated are both reusable but you want to watch out for object proliferation. I use this for pattern when the same data needs to be formatted or rendered differently or when you have a generic set of data fields that needs to be filtered based on some criteria.
  • Command – Used to encapsulate information that is used to call a piece of code repeatedly. Can also be used to support undo/redo functionality. The commands can be reusable across different product interfaces and act as entry points to invoke backend logic. For instance, I have used this pattern to support invocation of services from a self-service portal and interactive voice response channels.

There are additional patterns that help you organize your application code better (such as Model, View, Controller (MVC) and avoid point to point coupling between applications (publish/subscribe) fostering reuse.

what patterns have you used?

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