a) Discuss the different tiers/layers that make up a typical enterprise system design. Include a diagram as part of your discussion. 

b) Based on the answer given to Question 3(a), briefly discuss one reason why such a division is necessary for enterprise systems.

c) Compare and contrast the Singleton and Registry patterns as object-oriented design approaches. Include in your discussion the problems these patterns solve and whether they solve the same type of problems. Provide an example that demonstrates any similarities or differences that exist between the two patterns.

d) Compare and contrast composition and inheritance as object-oriented design approaches. Include an example that demonstrates any strengths or weaknesses of the two approaches and how using either composition or inheritance solves the design problems.