Monday, 16 November 2009

SOA Manifesto rambilings part 2 (the value statements)

The value statements reflect a desired prioritization of one value over another. It does not mean that the value that has a lower priority is not important it just means that the value with higher priority is seen as more important. The value statements are there to help prioritize key decisions. For example having a technical strategy with no business value makes little sense. But a technical strategy to support business value makes huge sense. Equally having project specific goals make sense but not at the cost of strategic goals. Should the need arise to support project specific goals over strategic goals then the decisions should be made with our eyes wide open.

Business value over technical strategy”

SO and SOA is not about technology. One may use technology to deliver it. The value is the value that the business identifies or agrees to. In the world of Enterprise Architecture and Solutions Architecture we measure the outcome of deliverables against agreed business expectations. The technical strategy that is employed is created based upon what we need to focus on technically to deliver business value. Many projects fail because they loose sight of the alignment with business imperative. Ensuring alignment to business value is the key to good governance.

“Strategic goals over project-specific benefits”

In the world of effective Enterprise Architecture applied to a business landscape, we seek to understand the vision of the enterprise and we seek to understand the mission statement. The vision is aspirational and forward looking, the mission is actionable and focused on the immediacy of the enterprise. The vision and mission are used to frame strategic goals for the enterprise. The strategic goals might be implemented by one or more programs of work within the IT space of an enterprise. These programs might incorporate many projects. One of the roles of an Enterprise Architect is to ensure that the programs align to the strategic goals and that the projects reflect them. Without the transparency and traceability of strategic goals to the vision and mission, projects cannot expect to deliver against them. Drift is a common concern and when siloed projects drift away from the strategic goals and focus on short term issues at the expense of the bigger picture. The result is a more costly solution as it has to be re-factored and/or re-built sooner than was anticipated because it failed to meet the strategic goals.

“Intrinsic interoperability over custom integration”

The easier and faster it is to compose new capabilities the more cost effective IT becomes in supporting the business and its changing needs. If we always have to place a mediator between services to reuse them then we are falling into the trap of custom integration and what this tells us is that the design of our services does not support intrinsic interoperability. From a principle perspective, moving to a more document centric approach encourages greater interoperability but compromises the ease of use or understanding of a service's capabilities. Probably no where else in designing services is it more important to get the functions and the types of the parameters correct and indeed to be unafraid of re-factoring over time to move towards greater intrinsic interoperability.

“Shared services over specific-purpose implementations”

The granularity of services in an implementation of an instance of a SOA is a common cause for concern. Reuse and therefore the sharing of capabilities through the embodiment of services and their contracts seems to be much harder than anticipated. Several methodologies have been espoused to help. What we all know instinctvely is it is never a good idea to re-develop the wheel. But of course we constantly re-develop the car. Cars are created through the composition of many existing components. The new Beetle makes use of the Golf chassis, but it feels like a very different car. Services as components for the construction of new capabilities is a key principle of SO but doing it is harder that saying it. What is needed is good component repositories with good documentation and reviews. Back in the 1980’s Shlaer and Mellor had the same idea but expressed it as a book of components, like those that electrical/electronic engineers might use, for things we use to create new capabilities. Sometimes a customer implementation is needed but it is not that often and measurements of customer implementation vs reuse should always be made on a regular basis to ensure that the benefits of shared services are being realised.

“Flexibility over optimization”

There is an old software proverb that rings true. Make it work before making it fast. Making things flexible, choosing where the points of flexibility need to be is not easy but by following some simple principles we can at least move much of what is needed outside of code making services configurable. Business rules can be used in place of coded logic, orchestration can be used in place of hardwired configuration. A heuristic approach that might be in a document for service implementers would be to ensure that business rules and processes stated in requirements are exposed to enable them to be changed.

“Evolutionary refinement over pursuit of initial perfection”

The old adage of don’t try to boil the ocean comes to mind. We always seek perfection but we always need to temper it with the realisation that perfection is a focus not a goal. Good software projects and programs are phased. Occasionally we have the big bang approach but they rarely succeed. So we need to be mindful that we cannot do it all in one go and so phase the approach. It is common for many SO projects and programs to be led by the user interface inwards. Service enabling as you go is a better approach than trying to service enable and then figure out how users interact with the service. This is the case because without the users we cannot be sure of the pain point the wishes and desires of those users and so cannot address their concerns. And it is the users (customers) that matter.

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