Characteristics of Database Tables:
A relational database consists of a collection of tables.
Each table has
- a heading or definition part and
- a body or content part.
The heading part consists of the table name and the column names. For example, a student table may have columns for
social security number, name, street address, city, state, zip, class, major and GPA. The body shows the rows of the table. Each row in a student table
represents a student enrolled at a university.
Once you have created entities representing the business objects you want to represent in your database,
you need to create tables to store the data in the database. Tables are made up of rows and columns.
Each column corresponds to an attribute of the entity to which the table refers.
Every row represents an instance of the entity described by the database table.
Specific data relating to each attribute is stored in the rows corresponding to each column.
The following interactive graphic shows a table that contains information about personal computers and points out the components of the table.
Mouse over each of the red circles to read about each of the attributes.
In order for a relational database to function properly, table rows and columns must follow a number of rules
grounded in the mathematical discipline of set theory
The next few lessons review those rules (in non-mathematical language whenever possible), but for now it
is enough to know that the rules exist and that they are practical.
Because relational databases are based on set theory, you may encounter the formal terms for database tables and
their components in the literature of set theory. Here are the terms you are most likely to see:
Database Tables are referred to as relations.
The columns of a table are referred to as attributes or fields .
Rows are referred to as tuples (pronounced tup-pulls ) or records.
record: A particular instance of the subject of a table.
The term relational database comes from the mathematical term relation (the definition of a two-dimensional table),
not the fact that tables can have relationships between them.
There are two basic types of tables in a relational database:
base table: A table stored in a database.
System base tables are the underlying tables that actually store the metadata for a specific database.
virtual table: A table stored in the memory of a computer. Virtual tables themselves are not stored
in the database; rather, the definition of the view is stored and given a name.
Users call up that name, and the view is created (from base tables) on the fly.
When a user closes the view, the virtual table is deleted from memory, only to be recreated the next time its name is invoked.
Before moving to the next lesson, click the Quiz link below to check your understanding of relational
constructs and the characteristics of tables.
Relational Table Characteristics - Quiz