Online Transaction Processing

A relational database is constructed using a component called a table. A table is a two-dimensional structure that contains data arranged in rows (tuples) and columns (domains). A table contains a data set (set).

Rows contain fields, the values of which, describe an organization, person, activity, location or thing. Rows also contain a field, referred to as the primary key, that uniquely identifies each row in the table and is used by the database management system to store and retrieve a particular row or group of rows in or from the table. The primary key is a proper key when it is a unique number.

There are two sets of terms used in the analysis and design of databases. One set describes the logical business elements during the analysis phase and one set describes the physical database elements during the design phase.

An entity is discovered during analysis and becomes a table during design.

An attribute is discovered during analysis and becomes a field during design.

An identifier is proposed during analysis and becomes a key during design.

The reason for two sets of language is that the language of analysis may be used to specify databases in architectures that don't have tables or fields. Also, if we start calling things tables, keys, and fields during the analysis phase, we are subconsciously making design decisions prematurely. This is particularly true of keys, since database design is primarily about the designation and placement of keys. If keys are mentioned during analysis, they are always referred to as "candidate keys". They don't become keys until design.