Other Languages

Other Languages
Although the relational calculus is hard to understand and use, it was recognized that its
non-procedural property is exceedingly desirable, and this resulted in a search for other
easy-to-use non-procedural techniques. This led to another two categories of relational
languages: transform-oriented and graphical.
Transform-oriented languages are a class of non-procedural languages that use relations
to transform input data into required outputs. These languages provide easy-to-use
structures for expressing what is desired in terms of what is known. SQUARE (Boyce
et al., 1975), SEQUEL (Chamberlin et al., 1976), and SEQUEL’s offspring, SQL, are all
transform-oriented languages. We discuss SQL in Chapters 5 and 6.
Graphical languages provide the user with a picture or illustration of the structure of
the relation. The user fills in an example of what is wanted and the system returns the
required data in that format. QBE (Query-By-Example) is an example of a graphical language
(Zloof, 1977). We demonstrate the capabilities of QBE in Chapter 7.
Another category is fourth-generation languages (4GLs), which allow a complete
customized application to be created using a limited set of commands in a user-friendly,
often menu-driven environment (see Section 2.2). Some systems accept a form of natural
language, a restricted version of natural English, sometimes called a fifth-generation
language (5GL), although this development is still at an early stage.