Database Reference
In-Depth Information
Storage
of Data
Relational Model
RELATIONS
Tuples
Attributes
Primary Keys
Foreign Keys
Data
Dictionary
DDL
Data
Files
Add/
Change/
Delete
Data
Usage
of Data
Figure 13-4
DML component: data maintenance.
Storage
of Data
Relational Model
RELATIONS
Tuples
Attributes
Primary Keys
Foreign Keys
Data
Dictionary
DDL
Data
Files
Retrieve/
Add/
Change/
Delete
Data
YES
NO
Usage
of Data
Figure 13-5
DCL component.
the database to authorized users not only for data retrieval, but also for adding,
changing, or deleting data.
Figure 13-5 shows the features of the DCL component and how this component
supports authorized data manipulation.
Languages for the Relational Model
As mentioned above, SQL has established itself as the preferred language for the
relational model. Before we discuss SQL in detail in the next section, it is worth-
while to briefly introduce a few other commercial languages that support the
relational data model. This introduction will give you some insight into the purpose
and features of the language components that support the various aspects of data
model implementation.
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