Principles

Design Pattern Principles: SOLID

*S: SINGLE RESPONSIBILITY PRINCIPLE - SRP
	A class should have only a single responsibility (i.e. only one potential change in the 
	software's specification should be able to affect the specification of the class).

	The single responsibility principle states that every class should have responsibility
	over a single part of the functionality provided by the software, and that responsibility
	should be entirely encapsulated by the class. All its services should be narrowly aligned
	with that responsibility.

*O: OPEN/CLOSED PRINCIPLE - OCPs
	“software entities … should be open for extension, but closed for modification.”

*L:	LISKOV SUBSTITUTION PRINCIPLE - LSP
	“objects in a program should be replaceable with instances of their subtypes without altering
	 the correctness of that program.”

	Liskov's notion of a behavioral subtype defines a notion of substitutability for mutable
	objects; that is, if S is a subtype of T, then objects of type T in a program may be
	replaced with objects of type S without altering any of the desirable properties of that
	program.

*I: INTERFACE SEGREGATION PRINCIPLE - ISP
	“many client-specific interfaces are better than one general-purpose interface.”

	The interface-segregation principle (ISP) states that no client should be forced
	to depend on methods it does not use.[1] ISP splits interfaces which are very
	large into smaller and more specific ones so that clients will only have to know
	about the methods that are of interest to them.

*D: DEPENDENCY INVERSION PRINCIPLE - DIP
	One should “Depend upon Abstractions. Do not depend upon concretions.”

	A. High-level modules should not depend on low-level modules. Both should depend on 
	   abstractions.
	B. Abstractions should not depend on details. Details should depend on abstractions.

[http://en.wikipedia.org/wiki/SOLID]