What is SOA?

When business increases and becomes complicated, we need IT to sort out things. It enables us to create custom solutions which increases our productivity. Now with IT in place, when the business needs to change/do M&A/etc. the applications developed by IT dept is a roadblock, as it cannot magically start working as per new requirements, and changing the applications takes long time and of course lots of money. Thus, IT becomes a constraint for business to grow.

SOA (Service Oriented Architecture) is a new approach to building IT systems, It uses existing assets and enables change. SOA is suppose to liberate business from the constrains of technology. It lets the business focus more on business and less on technology.

Current IT systems suffer from the following complications:

1. Business logic and plumbing
   One of the biggest problems in programming is that it is very difficult to keep the business logic separate from the plumbing because you need to control both at the same time. Though the tasks are related, they can be separated. It’s work, and it requires both the use of appropriate software tools and programmer discipline to ensure that the business logic is kept separate from the technology that makes it happen.
   For example, if you want to change the order in which particular business functions happen, and you’ve kept your business logic separate from your plumbing, making these changes is no big deal in a SOA. But if your business logic and your plumbing are one giant application, changes are costly and complicated, take time, require extensive testing, and are a very big deal indeed.
2. Legacy Systems
   Business in many cases will depend on legacy systems which are in place and operational, and business does not have time or budget to start from scratch.
   With SOA, you can use almost all your existing business applications. True, you may need to change them a little in order to include them in a SOA, but it is possible, and it is not all that hard. For example, you can treat an entire application as a service, or you can take some code out of an application and make just that code into a service.
   A SOA uses very specific, industry-agreed upon standards to create interfaces that make it possible for various components of the SOA to talk to each other.
3. Application archaeology
   It may not be possible to separate out business logic and plumbing as many of
   the business layer components come from existing applications, and existing business applications were likely built in very different ways, at different times, by different people, and for different reasons, maybe even using different computers. Unlike hardware, software hangs around for decades.
   Intelligent black-boxing is an important aspect of SOA. With a SOA, you can build a whole new computing environment by using all the resources that you already have by treating many components as black boxes. Particularly, you need to treat existing application components as black boxes, making them accessible by adding adapters. For example, you should use a black box to include older plumbing components that still work. The black box prevents you from spending money to replace something that works just fine. Or, as the sages say, “If it ain’t broke, don’t fix it.
4. Who’s in charge
   If the plumbing for one component doesn’t work with the plumbing for several other components, how will an end-to-end process work? If it fails, how will you know?
   Any and all problems associated with the end-to-end processing of components are dealt with by a little something called the SOA supervisor. So, no need to worry, because the SOA supervisor will take care of things. The SOA supervisor acts something like a traffic cop and helps prevent SOA accidents.

So, technically, a service oriented architecture is an architecture for building business applications as a set of loosely coupled black-box components orchestrated to deliver a well-defined level of service by linking together business processes.