That means that some piece of software is used to create, modify, save, and query the database. It's as if Microsoft Word were called a textual processing modification system , or the way they call shampoo a scientifically formulated hair therapy system . On the other hand, in the interests of accessibility, the reality is that many readers may already have their database in Access format and wish to at least practice generating Perl-based queries within the Windows environment.
Access is also an easy path to familiarity with relational databases.
It is SQL which defines the syntax and grammar, a sort of mini-programming language, with which you construct queries of the database. This article isn't an appropriate place for a full-fledged course in SQL programming, but you will need to know how to construct SQL statements. Ultimately, you'll be passing these statements from your Perl script to the database. A good web-based tutorial for SQL is James Hoffman's Introduction to Structured Query Language which will take you beyond the simple introduction to SQL presented here. Because this is a relational database, we can also construct slightly more complex SQL statements which relate data across both tables, billing and invoice s.