Natty Gur

Actually there are two aspects that we tend to follow when downsizing legacy system. The first aspect is business logic and the second is system design.

This is a simple test that I use to get basic insight whether system is built on solid OO approach, and adaptive to further changes. Using those questions while interviewing system owner gives me indication about OO level of the system and system adaptively level.

How many times you use third party library that implement any given task such as state machine, logging, Concurrency Utilities, etc’? Eventually you manage to find the right package for your needs and integrate it into your system. Every thing looks great until you find out that the chosen package needs to be replaced for some reason. The problem now is that you need to change your system code in order to use the new package because the new package based on other API and interfaces to interact with.

There are two main architectural pattern regarding application structure. The most common one is Layer patter. Layer suggests that you will organize your code in layers which characterize certain system aspect and responsible to carry out that system character. System is building from those layers one on another while the upper layer responsible to receive incoming request (Usually User Interface - UI layer) and return results. The request is processed by calling other system layers to perform their layer specialty as part of the process. Every layer should call only layers near the calling layer, no direct calls over layers should be made. In the end of the process the upper layer return results back to the caller. The most classic separation is to 3 layers a. Presentation – responsible for receiving client request and displaying process data. B. Domain logic also known as Business logic – holds system logic. C. Data access – Retrieving and update system data.

Here's my point of view : there are two main steps while designing a system. The first one is architecture and the second one id designing.