People who create computer software practice the art or craft or discipline that is software engineering. But what is software engineering "practice"? in a generic sense, practice is a collection of concepts, principles, methods, and tools that a software engineer calls upon a daily basis. Practice allows managers to manage software projects and software engineers to build computer programs. Practice populates a software process model with the necessary technical and management how-to's to get the job done. Practice transforms a haphazard unfocused approach into something that is more organized, more effective, and more likely to achieve success.
Core principles
The dictionary defines the word principle as "an important under law or presumption required in a system of thought" through this book we discuss principles at many different levels of abstraction. Some focus on software engineering as a whole, others consider a specific generic framework activity (eg, customer communication), and still others focus on software engineering actions (eg, architectural design) or technical tasks (eg, write a usage scenario). Regardless of their level of focus, principals help us establish a mind set for solid software engineering practice. They are important for that reason.
First principle: the reason it all exists
A software system exists for one reason: to provide value to its users. All decisions should have been made with this in mind. Before specifying a system requirement, before nothing a piece of system functionality, before determining the hardware platforms or development processes, ask yourself questions such as: does this add real value to the system? If the answer is no, do not do it. All other principals support this one.