Sunday, September 28, 2008

Business Agility

Business agility (along with business-IT alignment) is often touted as one of the key benefits of SOA. The problem is that more often than not no explanation is given for what business agility actually is, why it is important, or how SOA contributes to achieving it.

Firstly, it is important to note that business agility is a relative goal as opposed to an absolute one. Even the most agile business can strive for greater agility.

So what is business agility? Business agility is the degree to which an organisation can effectively innovate and respond to market forces.

In any given undertaking within an organisation, there are the traditional project management constraints of time, resource, scope and quality. For a fixed scope if we wish to decrease time to delivery, we must increase resource or decrease quality. For fixed resource if we wish to decrease time to delivery, we must decrease scope or quality.

Note that scope refers to the amount of work that needs to be done to deliver the agreed outcome. But as always, there is more than one way to skin a cat. The business objectives targeted by the project can be met in any number of different ways. A talented Solution Architect can design a solution to a business problem that requires less work to deliver.

Really what we are talking about here is contrasting business value with effort. If an organisation has a highly complex IT architecture that is very tightly coupled with a large number of interdependencies, then a change will take more effort to achieve, but deliver the same business value.

In order to have an agile organisation, we must have the ability to enact change with less effort. SOA helps simplify the IT architecture of an organisation by making systems more loosely coupled. Of course, there are varying degrees of loose coupling with different SOA implementations.

The SOA architectural style reduces coupling through message based interactions conforming to explicitly defined service contracts that encapsulate the implementation details of services away from consumers. This gives us the ability to make changes to service implementations without impacting their consumers.

We reduce coupling further by designing our services with appropriate granularity and cohesion, based on publish-subscribe messaging with stable service contracts.

The IT architecture of an organisation however is only one piece of the business agility puzzle. Once a business need has been identified, the business requirements must be extracted. The speed, efficiency and accuracy with which this activity is performed also contribute to business agility. There is very little business value in delivering a solution that doesn't meet the identified business objectives.

Furthermore once we have extracted our business requirements, assuming they are accurate, we need to produce a solution architecture that meets those requirements. So an organisation's proficiency in Solution Architecture is also significant here.

We also want to ensure that as each solution is delivered, the complexity of the business and IT architecture is not adversely affected. As such, we need the proper architecture governance processes in place to protect the broader enterprise architecture.

It is important to strike the right balance with governance however. Inefficient governance processes slow the rate at which projects can be delivered, thus harming business agility. Insufficient governance however will result in the gradual increase of architectural complexity, thus harming business agility in the long run.

Simply developing an effective solution architecture is still not enough. We must of course then go about implementing the solution. Here, the effectiveness of the organisation's project and programme management function is relevant, as well as the proficiency of the people that build and deploy the solution.

And finally once the solution is ready to deploy, there must be effective change management processes in place to ensure that affected workers are properly trained and informed to support the change. If the solution is not embraced by the people it affects, then the change will be ineffective.

So why all the fuss about business agility? Simply put, an organisation that doesn't respond to its changing environment will eventually become uncompetitive. Granted that some industries are more volatile than others, however all business environments change over time. Those businesses that are able to embrace this change in order to generate competitive advantage will be more successful.

Innovation is also a key consideration in generating competitive advantage. The ability to be able to take an idea and turn it into reality in less time, with less cost and lower risk certainly generates competitive advantage.

So in conclusion, SOA as a style of architecture contributes towards business agility through reduction of enterprise architectural complexity, but by no means guarantees it.

Friday, September 26, 2008


So far I've posted a large amount of material on SOA, pushing very heavily for an event driven approach - with specific attention to business services, where business-relevant events are surfaced as event messages published over a service bus.

There has been an ongoing discussion in the public forum around the relationship between SOA and EDA (Event Driven Architecture). Are they in fact separate architectural styles? Are they separate concerns? Do they complement each other? Does SOA subsume EDA?

SOA and EDA are in fact separate architectural styles. However they describe different concerns of an architecture. They each bring their own benefits. As such, it is possible (and in fact good practice) for the two styles to overlap. An architecture can indeed both be service oriented and event driven. Likewise it is possible for an architecture to be service oriented but not event driven, or event driven and not service oriented. This is illustrated below.

An architecture consisting of services with no endpoints with a publish-subscribe binding conforms to the service oriented style of architecture, but is not event driven. An architecture consisting of messages published over topics, but where there is no notion of services is event driven, but not service oriented. For example, EAI can be achieved by having a number of applications publishing and subscribing over a set of topics, without explicitly defining any services, endpoints or service contracts.

Where SOA and EDA come together, a topic corresponds to a specific endpoint of a specific service. A topic cannot be shared between endpoints or services, and messages published onto a topic must conform to an explicitly defined service contract. SOA brings benefits to EDA and vice versa. Therefore we get the best result when the two architectural styles are combined.

Wednesday, September 17, 2008

Service Composition (continued...)

In my last post we talked about service composition in SOA. Miguel posted a good question about whether composition in SOA is analogous with composition in Component Oriented Programming. This really got me to thinking about whether composition actually has any real meaning in SOA at all.

One of the key differences between components in Component Oriented Programming and services in SOA is that components must be instantiated. A client must instantiate a component before the component is used. Furthermore, multiple instances of a component can and usually do exist at the same time.

Composition makes a lot of sense in Component Oriented Programming because we have one or more child components supporting a parent component. Every new instance of the parent component contains new instances of the child components.

Without instancing, composition wouldn't really make a great deal of sense in Component Oriented Programming. Just because a component uses or references another component, doesn't make those components a composite. What makes a set of components a composite is the lifetime of the child components being indelibly tied to that of the parent component. The children are created with the parent and destroyed when the parent is destroyed. The children have no purpose other than to meet the needs of the parent.

SOA is a different ballgame however. There is only ever one and only one instance of every service. All services for all intents and purposes are always running (except for the odd moments of downtime) until those services are retired. So what is a composite in SOA terms? If I have a service A which consumes services B and C, is A a composite of B and C? I would say no. Otherwise all services in our enterprise would simply one big composite.

I would suggest that composition in SOA refers to the bringing together of lower level services in order to support one or more higher level services. It seems we need to have services at different levels in order for composition to make sense in SOA. So if services B and C are lower level services that form part of the implementation of service A, then I would say that services B and C have been composed to form service A.

As I mentioned in my last post, with all the hype around Layered Service Models, where lower level services (like task and entity services) are composed to form higher level process services, we see service composition taking centre stage in SOA discussions far more than it really should.

As I've previously discussed, the type of reuse central to Layered Service Models (functional reuse as opposed to reuse of events) doesn't really work very well in practice. Functions exposed at the service level generally are too coarsely grained to be reused in different contexts. As such, the notion of having a registry of lower level services that can be composed together in support of higher level services is somewhat flawed.

We may have lower level services such as integration services, UI services or B2B services that support a higher level business service, but those lower level services should not be reused between the higher level services. As such, in this case the service composition is really just an implementation detail of the higher level services and as such not really architecturally noteworthy.

So I say again, service composition in SOA is only really a noteworthy concept if you're pursuing a Layered Service Model which as I've said before is not ideal.

Friday, September 12, 2008

Service Composition

Quite often we hear of service composition as one of the key benefits of the service oriented style of architecture. With service composition, we are referring to the creation of new services from wiring up of existing services in new ways to deliver new value.

According to the standard reading material, service composition is best achieved through orchestration. This is usually achieved through the use of middleware such as an ESB or integration broker. A workflow orchestrates the invocations of a number of services in order to achieve some particular outcome.

As such, we find that a service may comprise some of its own logic (including the orchestration logic), as well as a number of lower level services.

This concept of service composition is central to the Layered Service Model where lower level task and entity services are composed into higher level process services. As you will have gleaned from my previous posts on the topic, I'm not a supporter of the Layered Service Model approach. One of the issues of this approach is that lower level services are reused by many higher level services, resulting in high coupling between those higher level services.

In the past, I have highly recommended that people pursue what I call a Self-Contained Process-Centric Service Model. Here, services are centred around autonomous business functions such as Sales, Marketing and Billing. What I probably didn't emphasise about this approach however is that it refers only to the top-level service model. Each business service may be composed of lower level services.

Note that these lower level services are not business services. They are services that serve a particular function in support of the business service. They are an implementation detail of the business service. In fact, they are actually really just distributed components or integration points. However if the means of communication with the distributed component or integration point is the exchange of messages via endpoints in conformance with a service contract, then we technically have a service by the strict definition of SOA.

In a green fields implementation where the software supporting each business service is built from scratch, there may be no lower level services involved. That is, there is no service composition. Alternatively, the service software may be implemented with a smart client application that interacts with some back end components via the exchange of messages in conformance to a service contract. Thus, those back end components technically expose a service to the smart client application.

Say in support of this business service, the back end components also interact with a Web service provided by another organisation. Now we have another service added to the mix. Here we can see services being composed in support of the larger business service.

Where a business service is supported by a number of legacy applications we see even more composition. When the business service receives a message, it must invoke one or more of these legacy applications appropriately. This may be achieved by invoking Web services exposed by these applications, thus constituting further service composition.

So we see that services certainly can be composed in support of larger services. However I would hesitate to name this as a benefit of the SOA style of architecture. It is merely an implementation choice of any given service. Service composition has only come to be viewed by many as a key benefit of SOA due to the reuse promised (falsely in my opinion) by the Layered Service Model approach.

Friday, September 5, 2008

Federated Identity Session Slides

Thank you to all those who attended the .NET Community of Practice session on Thursday evening. For those who missed it, you can download the presentation slides here.