ABSTRACT
In Chapter 2, the usefulness of relational tables was introduced. Sample data from the U.S. Environmental Protection Agency was used to show the advantage of storing each type of data in a separate table. The data in each table remain related to the proper chemical compound through the use of a unique chemical id, which functions as a unique key relating multiple tables. This technique will be used extensively in this and following chapters. The separation of data into multiple tables also facilitates cases where a compound may have multiple data values, also known as one-to-many relationships. This chapter will show examples of how many-to-many relationships are handled. It will also show more examples of how the choice of data types affects the operation of the database and the applications that use it.
