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Design: SOA Taxonomy, an object oriented approach

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An essential part of the SOA Governance is to properly identify the requirements in order to introduce or upgrade a service within your SOA model, this is commonly known and service and integration planning within the SOA lifecycle. This is all good in theory but the nightmares start when architects are trying to put it in practice.

As an application development consultant here at Microsoft we constantly find chaos in the SOA first attempts, the main reason behind this is the lack of services organization. This not only brings problems to the model that are expensive to change but does not shows business value to the stakeholders, as they cannot see any ROI in the implementation. As a result, the efforts are abandoned and the architectural model remains broken.

How do we help our customers to solve this issue? We usually take them a level higher within the abstraction layer, why do you need SOA? Which are the problems that you usually have? Which are the costs involved in changing your system? We really need to understand our driven forces that lead us to a new architectural paradigm.

But what about designing the services model? This is another area where confusion arises as architects ask themselves where they should start and how. The answer to this is enclosed on the services taxonomy. There are many categorizations and naming around taxonomy but I want to present a recommendation based on the Microsoft services experience.

We define four main categories that really help us to define the high level model. Let me explain each one of them.

· Entities Services: The entities encloses your business entities, these are independent actors within your business model. The entities do not provide business benefit acting alone as they don’t have the expertise around which other entities are around. They should be completely independent and should own the data repository. A good example of an entity service will be customers. Customers are nothing more than what the name says, it has and owns all the information about the entity “customer” but knows nothing about your business.

· Capabilities Services: This is the crucial part of your business; this is what you do to add value to your services. The capabilities know very well the entities and capabilities context where it works, as interacts and consumes services to deliver value. An important thing to understand is that they know about the capability but do not control the entities that consumes, this means that if a capability needs to alter an entity it should use the entity service responsible for that. The capability also owns its own repository and controls all the business logic associated with it. A good example of a capability is an order service. The order service will know everything about placing an order and will need entities in order to generate one, for example, the order will need the customer information that comes from the entity service.

· Application services: These services supports your business model, this means that provides auxiliary services to your entities and capabilities not directly associated with your system. This usually involves wrappers to third party application or bridges to other systems. A good example may be a service wrapper to a Remedy application.

· Bus services: This taxonomy groups all the support and infrastructure services that allow your entities and capabilities to work within the infrastructure policies. For example the security services that validate users can be grouped in this taxonomy.

 

As you see, with this categorization you can start to add services to your model. Where do you start? The easiest way to do it is asking yourself what your business does, what is the essence of it. Let’s imagine that you are the responsible for designing the SOA model for a large supermarket. The amount of services that you will need is massive but if I ask you about the essence of your business which will be the answer? Believe it or not this sounds easy but architects that are too embedded in the daily duties cannot properly answer the question. My model would be:

Look how simple it is, you just join customers with products and generate orders. Now, if I ask you to add these services in the taxonomy model you now know how to do it.

Remember that upon I have presented orders as the linking service between the entities this does not suggest hierarchy. All the services are at the same level as they can be accessed by an ESB (Enterprise service bus) or ISB (Internet service bus), or even simply your process layer. What is more, what you can do is apply the same model when you enter into the service design scope; this is for example when you design the internal taxonomy of “Orders”. This service will have again a process layer, entities and capabilities, but now only around the orders scope. Does this sound familiar? Well, it may, as it is a common model applied to the object oriented design.

Internally, these new entities and capabilities can be isolated components that are responsible for a solely function, for example, an internal process can be the workflow that triggers a new order and a capability may be altering the order value.

 

This can show you that applying the SOA governance model around taxonomy can help you and your developers to properly design services and object oriented components properly isolated and encapsulated, as is the same mindset. What is more, the WCF team is working in a “in-process” binding that will allow you to use a WCF communication with objects that today are part of your main process and tomorrow may develop into independent services just changing the configuration file! Isn’t it beautiful?

 

If your organization is facing these problems and you want Microsoft to support you and help you around your SOA initiative don’t hesitate the contact the “Application Development Consultant team” in Microsoft (https://www.microsoft.com/uk/adc)

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