Chemistry Reference
In-Depth Information
chapter 6
Data Storage, Searching,
and Manipulation
6.1 Introduction
A schema is a collection of tables and functions in a database. There is
no single schema that will satisfy the needs of every chemical database
user. It might be possible to use an existing schema, perhaps one from this
topic, and modify it to suit the needs of a particular project. It might be
necessary to examine the needs of the project and develop an entirely new
schema. The purpose of this chapter is to give examples of useful schemas
and to provide enough background to allow the design of new schemas.
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 data-
base and the applications that use it.
6.2 General Schema Design Decisions
When designing a schema to hold chemical information, it is crucial to
first consider how the data will be used. One approach is to interview
potential users of the database to determine what questions need to be
answered on a regular basis. For example, users of a chemical compound
tracking system will typically need to know the following:
•
Where is compound X now?
•
Which compounds does chemist Z have checked out?
•
Has compound Q already been registered?
•
How many samples of compound Y have been prepared?
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