Wednesday, January 14, 2009

Key Learnings:Drawing parallels between Design Patterns and the principles of SOA - Part II

This blog entry attempts to expand on the concepts explored in a prior blog of mine Key Learnings: Drawing parallels between Design Patterns and the principles of SOA that deals the relevance of design patterns in the world of SOA and services. Patterns explored previously were the Facade, Abstract Factory, Builder, Factory and Bridge.

In this blog we look at how infrastructure components like the ESB that are part of the service mediation layer insulate the service consumer from the service provider by offering call-dispatch functions that map out the most efficient call execution path for honoring a consumer business request। Many of the constructs of the service mediation layer provide add-on capabilities which are in fact model driven implementations of common design patterns।

Adapter - modifies an incoming method call to fit the required method signature or definition of the provider without impacting the consumer

Transformer - adapts the parameter and return type or message format (which includes alteration or interpretation of the message content) and enables the insulation of the consumer information from that of the providers'

Decorator - augments the behavior or is a facility to add on to the behavior without altering the interface and breaking the service interface and service contract as new consumers need additions to the base business behavior

Interceptor - provides ancillary behavior, filters out information or calls to the provider, validates the message content for authN credentials, authZ/ entitlements and permissions etc। all of which provide important ancillary behavior to the provider without having the providers' service implementation layer having to be peppered with nonbusiness logic level code।

Finally, the point of this blog is to show that despite vast numbers of changes in technologies and technology based service offerings the basic design principles and design patterns of the object oriented design realm are still applicable। Knowing these and applying these carefully enables one to retain the durability of the service interface and protects the consumers from unexpected or non-deterministic results and exceptions.

Thank you for listening. Your input is invaluable!

- surekha

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