Software Engineering for Students A Programming Approach

176 Chapter 14 ■ The basics
and actions. The data description and manipulation facilities of a programming language
should therefore allow the programmer to represent “real-world” objects easily
and faithfully. In recent years, increasing attention has been given to the problem of
providing improved data abstraction facilities for programmers. We discuss this in
Chapter 15 on programming language features for OOP.
As we shall see, most mainstream programming languages have a small core and all
the functionality of the language is provided by libraries. This chapter addresses this
core. Facilities for programming in the large are reviewed in Chapter 16. Other features
of languages – exceptions and assertions – are dealt with in Chapter 17.
14.2 ● Classifying programming languages and features
It is important to realize that programming languages are very difficult animals to
evaluate and compare. For example, although it is often claimed that language X is a
general purpose language, in practice languages tend to be used within particular
communities. Thus, Cobol has been the preferred language of the information systems
community, Fortran, the language of the scientist and engineer, C, the language
of the systems programmer and Ada, the language for developing real-time or embedded
computer systems. Cobol is not equipped for applications requiring complex
numerical computation, just as the data description facilities in Fortran are poor and
ill suited to information systems applications.
Programming languages are classified in many ways. For example, “high-level” or
“low-level”. A high-level language, such as Cobol, Visual Basic or C#, is said to be
problem-oriented and to reduce software production and maintenance costs. A low-level
language, such as assembler, is said to be machine-oriented, facilitating the programmer’s
complete control over the efficiency of their programs. Between high- and lowlevel
languages, another category, the systems implementation language or high-level
assembler, has emerged. Languages such as C attempt to bind into a single language the
expressive power of a high-level language and the ultimate control which only a language
that provides access at the register and primitive machine instruction level can provide.
Languages may also be classified using other concepts, such as whether they are weakly
or strongly typed. This is discussed below.
14.3 ● Design principles
Simplicity, clarity and orthogonality
One school of thought argues that the only way to ensure that programmers will consistently
produce reliable programs is to make the programming language simple. For
programmers to become truly proficient in a language, the language must be small and
simple enough that it can be understood in its entirety. The programmer can then use
the language with confidence, probably without recourse to a language manual.