Mauri Ltd has just acquired a new stock management system and the source codes (PhP5) also have been delivered. The coding style is fully object-oriented. The company has been using the system for two weeks and is not satisfied with it. For each user accessing the system, a new connection is made. The User Interface (UI) is not standard. Each update to the database is treated by a separate program. Search facilities have been included but different programs have been written to provide such facilities. You have been asked to refactor the system using Design Patterns.

(a) Identify five design patterns that can be used. Describe how each pattern can be used in the above context. Your answer should consist of a detailed description of the pattern including the structure (diagram) and a justification for its use. Note: Sample codes may be used to explain your answer.

(b) "Familiarity sometimes keeps us from seeing the obvious." In what way can patterns help avoid this?

(c) What are three reasons that cause requirements to change?

(d) What could Christopher Alexander discover by looking at structures that solve similar problems?