Conceptual Explanation

A standard database consists of one or more tables. Tables hold records. Records are made up of fields, also called attributes. If you visualize a table in terms of rows and columns, the records are the rows and the columns are the fields. To use nontechnical language, each record defines one thing, with each field in the record holding a different attribute of that thing. Each table holds records of a single type, and each record has the same set of attributes. In databases incorporating more than one table, an attribute of records in one table might consist of pointers to records in another table. The technical, all-encompassing term for thing or type is entity. An entity can correspond to a physical object or an abstraction with meaning within the organization. The technical term for the situation in which attributes in records in one table refer to records in another table is relationship.

Entity Relationship (ER) diagrams are ways to plan and to document databases. The boxes hold information on the fields making up the records in each table. The lines connecting the boxes represent relationships between tables. Marks and numbers on the connecting lines indicate what is called the cardinalities of the relationship. These are the minimum and the maximum number of records in the table at one end for each record in the table at the other end. In most cases, the counts are 0, 1, or many.

Normalization is a process by which a systems designer examines and, possibly, modifies a design. You will read later about the requirements for a database design to be in first, second, and third normal form.