Database Reference
In-Depth Information
Storage
of Data
Relational Model
RELATIONS
Tuples
Attributes
Primary Keys
Foreign Keys
Usage
of Data
Figure 13-1
Aspects of data model implementation.
Figure 13-1 illustrates these two major aspects of implementing a data model
as a database system. Note the model components on the left side of the figure
and see how implementation of the data model provides for data storage and data
usage.
Role of Languages
How is the implementation of a data model as a database system accomplished?
Accomplishing the implementation includes storage of data and usage of data. You
need a method, a medium, a language component for providing for each of the
aspects of implementation. You must have a language component to support data
storage; you need a component to enable the usage of data. In addition to these two
primary requirements, there must be language components for some other aspects
as well.
Let us review each of these aspects of model implementation and note the
desired features of the language components. Note how each component serves a
distinct purpose and understand how all these language components together make
the implementation of the data model happen.
Defining Data Structure
To store data, you need to define the data structure
to the database management system. Data definition for the relational data
model includes defining the logical model components as well as physical model
components. The data definition language (DDL) module supports the storage of
data in the database system.
Figure 13-2 shows the features of the DDL component and illustrates how this
component enables data storage.
Data Retrieval
Once the data structure is defined and the data are stored in the
database, we need a language component to enable usage of the data. Data access
is part of the overall ability to manipulate the data in the database. This part of the
data manipulation language (DML) component enables retrieval of data from the
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