Database Reference
In-Depth Information
an entity is represented by a table, which is a logical structure containing a set of related entity
instances. A column in a table is corresponding to an attribute in an entity. A row in a table is an
entity instance in a data model. Another set of names corresponding to entity, attribute, and entity
instance are called ile, ield, and record, often used in ile system processing and programming
languages by programmers.
A converting process from a data model to a relational database converts the data model com-
ponents to the database objects and implements the relationships among the database objects.
Figure 3.1 shows a table that consists of rows and columns.
As seen in Figure 3.1, each cell in the table contains a data value. For each column, the data
values have the same data type. he data type of the column LocationID is integer. he data type
of the column Name is character. he data type for the column CostRate is money, and the data
type for the column Availability is decimal. For the column ModiiedDate, the data type is date-
time. he deinition of the table is shown in Figure 3.2.
It is easy to confuse the word
relation
with the word
relationship
in an E-R model. he word
relation
is closely related to
table
. For a
table
to be a
relation
, each cell in the table must contain
a single value, there should be no duplicated rows, and all the cells in a column must contain the
Figure 3.1
Example of table.
Figure 3.2
Table deinition.
