Database Reference
In-Depth Information
Although all DBMSs have similar functions and features, they are not all the
same. There are subtle but significant differences. DBMSs may be broadly classified
based on the following criteria:
•
Meant for single user or multiple users
•
Physically linked (hierarchical, network) or logically linked (relational)
•
Whether based on inverted file structure with interfile connections
•
Whether restricted to specific data models (hierarchical, network, relational,
object-relational)
•
Intended for centralized or distributed databases
•
Based on the type of data distribution (homogeneous, heterogeneous, or
federated)
•
General purpose or special purpose
Languages and Interfaces
Let us now elaborate on the means by which database practitioners and users inter-
act with the database. They require interface mechanisms to access the database.
The database administrators need languages to manage the database; users need
languages to access the database. Figure 2-6 indicates the interface mechanisms for
interacting with the database.
Let us examine the different types of languages and interfaces and study their
functions. Each type serves a distinct function.
Data Definition Language (DDL)
Database administrators use DDL to define
the data structures and store the definitions in the data dictionary also known as
the data catalog. DDL provides language syntax for defining the conceptual and
external schemas. Specifically, DDL includes features to define the following:
DBMS: LANGUAGES / INTERFACES
Data Definition Language
Data Manipulation Language
Enterprise
Data Control Language
Database
Query Interface
Report Writer
Application Developer
Figure 2-6
Languages and interfaces.
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