A database can be defined as a collection of related data (Elmasri and Navathe, 2010). Databases are often subcategorized as SQL databases or NoSQL databases. In SQL databases, data is recorded in tables and consists of rows and columns. The related data may be distributed across several tables in a trade-off between efficient storage and convenience. The database management system (DBMS) is a piece of software that enables the database to serve several functions. For one thing, it allows for the retrieval of data using the SQL language (for SQL databases). Another function is to update the data when needed, also using SQL. Additional functions of a DBMS include protecting and securing the data.

Database management is a complex field of its own. In this book, we will place an emphasis on using SQL to retrieve and update clinical data that is usually distributed across multiple related tables. For additional comprehensive resources on databases, see the References section at the end of this chapter.