The Relational Model and Normalization - Database Processing: Fundamentals, Design, and Implementation - page 121

Figure 3-3
Important relational Model
terms

Important Relational Terms

Relation

Functional dependency

Determinant

Candidate key

Composite key

Primary key

Surrogate key

Foreign key

Referential integrity constraint

Normal form

Multivalued dependency

By The WAy In Figure 3-4 and in this discussion, we use the term entity to mean
some identifiable thing. A customer, a salesperson, an order, a part, and
a lease are all examples of what we mean by an entity. When we introduce the entity-
relationship model in Chapter 5, we will make the definition of entity more precise. For
now, just think of an entity as some identifiable thing that users want to track.

Characteristics of Relations
A relation has a specific definition, as shown in Figure 3-4, and for a table to be a relation, the
criteria of this definition must be met. First, the rows of the table must store data about an entity
and the columns of the table must store data about the characteristics of those entities. Next, the
names of the columns are unique; no two columns in the same relation may have the same name.

Figure 3-4
Characteristics of relations

Characteristics of Relations

Rows contain data about an entity.

Columns contain data about attributes of the entities.

All entries in a column are of the same kind.

Each column has a unique name.

Cells of the table hold a single value.

The order of the columns is unimportant.

The order of the rows is unimportant.

No two rows may be identical.