Introduction Although many varieties of sophisticated software are available for database construction, they impose very little restriction on their implemented form. Indeed, it would fly in the face of database philosophy to impose the form of implementation, for this would not encourage features like responsiveness to new requests (Bailey, Creel, Grossman, Gutti, and Sivakumar, 55-57). Thus each operational database is unique, even if the software used in constructing it is an industry standard. A piece of advice one gets from software manuals is to develop two mental pictures of one’s unique database. The first picture is of the contents of the database and the way it is organized; and the second picture is of what can be done with
Problem depiction The data are simply a set of tables. These tables may be manipulated by an algebra or a logical calculus. However, on the grounds of simplicity, a language which is as similar to English as possible is to be preferred. The best known of such languages is SQL(Structured Query Language) first developed by IBM for internal purposes, but now used much more widely. The full ‘vocabulary’ is rich and extensive, but here it is necessary to do no more than illustrate the use of a very limited part of it. The basic building block of the SQL language is the ‘select’ command. For example, if numerical and categorical data on firms in 1985 are gathered in the type 1 record of the database relating to the AQ 1985, and denoted as level 1, a select statement might take the form: select firm sic employ trainno from 1 where employ le 2 (Grossman, Creel, Mazzucco, and Williams, 115-120) One is interested here in firms at the very lower end of the size distribution, for which employment is less than or equal to (i.e. ‘le’) 2 persons. For such firms, one wants to know whether they take on trainees, and if so, how many. Further, one wants to know which industrial classification (SIC code) each of these SBEs lies within. This sort of information might be relevant to an analysis of training functions in an enterprise culture. It is possible to report, having implemented the above