Always design your software in components. This way you will be able to benefit from re-use and be able to build applications using these legos very quickly. Your applications will also be error-proof since these building-blocks will have already been tested before.

AFter you specify your subject areas in data design try to identify business methods and then build and test them. These methods, or components in other terms, can be either subtracnsactional or transactional.

• subtransactional components: These are components that comprise a certain business logic and leave the business consistent. You can think of subroutines or functions as exapmples for subtransactional methods. These methods are those to be used or called from other components...
• Transactional methods: These are standalone programs or procedures or client/server programs and have their own user interface (GUI). These are parts of the application that will mainly use one or more of the subtransactional methods to perform a certain task...