Concepts of Data and Databases

A database intends to have a collection of data stored together to serve multiple applications as possible. Hence a database is often conceived of as a repository of information needed for running certain functions in a corporation or organization. Such a database would permit not only the retrieval of data but also the continuous modification of data needed for control of operations. It may be possible to search the database to obtain answers to queries or information for planning purposes.

What’s a database?

A database can be thought of as a kind of electronic filing cabinet; it contains digitized information (“data”), which is kept in persistent storage of some kind, typically on magnetic disks. Users can insert new information into the database, and delete, change, or retrieve existing information in the database, by issuing requests or commands to the software that manages the database—which is to say, the database management system (DBMS for short). Note: Throughout this book, I take the term user to mean either an application programmer or an interactive user or both, as the context demands.

Now, in practice, those user requests to the DBMS can be formulated in a variety of different ways (e.g., by pointing and clicking with a mouse). For our purposes, however, it’s more convenient to assume they’re expressed in the form of simple text strings in some formal language. Given a human resources database, for example, we might write:

EMP WHERE JOB = 'Programmer'

And this expression represents (let’s agree) a retrieval request—more usually known as a query—for employee information for employees whose job title is ‘Programmer’.