$1.2 A REVIEW OF EXTERNAL FACTORS 11 Efficiency is only one of the factors of quality;we should not(like some in the profession)let it rule our engineering lives.But it is a factor,and must be taken into consideration,whether in the construction of a software system or in the design of a programming language.If you dismiss performance,performance will dismiss you. Portability Definition:portability Portability is the ease of transferring software products to various hardware and software environments. Portability addresses variations not just of the physical hardware but more generally of the hardware-software machine,the one that we really program,which includes the operating system,the window system if applicable,and other fundamental tools.In the rest of this book the word "platform"will be used to denote a type of hardware-software machine;an example of platform is "Intel X86 with Windows NT"(known as "Wintel") Many of the existing platform incompatibilities are unjustified,and to a naive observer the only explanation sometimes seems to be a conspiracy to victimize humanity in general and programmers in particular.Whatever its causes,however,this diversity makes portability a major concern for both developers and users of software. Ease of use Definition:ease of use Ease of use is the ease with which people of various backgrounds and qualifications can learn to use software products and apply them to solve problems.It also covers the ease of installation,operation and monitoring. The definition insists on the various levels ofexpertise ofpotential users.This requirement poses one of the major challenges to software designers preoccupied with ease ofuse:how to provide detailed guidance and explanations to novice users,without bothering expert users who just want to get right down to business. As with many of the other qualities discussed in this chapter,one of the keys to ease of use is structural simplicity.A well-designed system,built according to a clear,well thought-out structure,will tend to be easier to learn and use than a messy one.The condition is not sufficient,of course (what is simple and clear to the designer may be difficult and obscure to users,especially if explained in designer's rather than user's terms),but it helps considerably. This is one of the areas where the object-oriented method is particularly productive; many O-O techniques,which appear at first to address design and implementation,also yield powerful new interface ideas that help the end users.Later chapters will introduce several examples.§1.2 A REVIEW OF EXTERNAL FACTORS 11 Efficiency is only one of the factors of quality; we should not (like some in the profession) let it rule our engineering lives. But it is a factor, and must be taken into consideration, whether in the construction of a software system or in the design of a programming language. If you dismiss performance, performance will dismiss you. Portability Portability addresses variations not just of the physical hardware but more generally of the hardware-software machine, the one that we really program, which includes the operating system, the window system if applicable, and other fundamental tools. In the rest of this book the word “platform” will be used to denote a type of hardware-software machine; an example of platform is “Intel X86 with Windows NT” (known as “Wintel”). Many of the existing platform incompatibilities are unjustified, and to a naïve observer the only explanation sometimes seems to be a conspiracy to victimize humanity in general and programmers in particular. Whatever its causes, however, this diversity makes portability a major concern for both developers and users of software. Ease of use The definition insists on the various levels of expertise of potential users. This requirement poses one of the major challenges to software designers preoccupied with ease of use: how to provide detailed guidance and explanations to novice users, without bothering expert users who just want to get right down to business. As with many of the other qualities discussed in this chapter, one of the keys to ease of use is structural simplicity. A well-designed system, built according to a clear, well thought-out structure, will tend to be easier to learn and use than a messy one. The condition is not sufficient, of course (what is simple and clear to the designer may be difficult and obscure to users, especially if explained in designer’s rather than user’s terms), but it helps considerably. This is one of the areas where the object-oriented method is particularly productive; many O-O techniques, which appear at first to address design and implementation, also yield powerful new interface ideas that help the end users. Later chapters will introduce several examples. Definition: portability Portability is the ease of transferring software products to various hardware and software environments. Definition: ease of use Ease of use is the ease with which people of various backgrounds and qualifications can learn to use software products and apply them to solve problems. It also covers the ease of installation, operation and monitoring