The relational model’s main venders evolved
the model further and crated the extended relational data model (ERDM). The
ERDM adds may of the object oriental model’s features within the inherently
simpler relational database structure. The
ERDM gave birth to a new generation of relational database supporting object
oriented features such as object extensible data types based on classes, and
inheritance. That’s why a DBMS based on the extended relational data model
(ERDM) is often described as a object relational data base management system
(O/RDBMS) it is important to note that not all data model are created equal.
Some data models are better suited than others for some tasks. For example
Conceptual models are better suited for high-level data modeling while
implementation models are better for managing stored data for implementation
purpose.
THE FUTURE OF DATA MODELS
The object/relational
data base management system (O/RDBMS) is the dominant database for business applications.
It’s success could be attributed to the model’s conceptual simplicity,
easy-to-use query language, high transaction performance, high availability,
security, scalability and expandability.
TWO EXAMPLES OF EVOLUTION
(i) Hybrid
DBMS: These types of database preserve the performance characteristics of the
relational model and the semantically rich programmatic support of the object
oriented model.
(2) SQL data services (SDS) on it’s Azure
services platform, are becoming a critical component of relational database
vendors internet service strategies.
THE EXTERNAL MODEL
The external model is the end user’s view of the data
environment. The term end users refers to people who use the application
programs to manipulate the data and generate information. companies are
generally divided into several business units, such as sales, finance and
marketing. Therefore, end uses working within those business units view their
data subsets as separate from or external to other units within the
organization. Also note that although the application views are isolated from
each other each view shares a common entity with the other view.
THE
CONCEPTUAL MODEL
A conceptual model is used, graphically represented by
an ERD to integrate all external views into a single view. And it can
represents a global view of the entire database as viewed by the entire
organization. It is also known as a conceptual schema, it is the basis for the
identification and high-level description of the main data object.
the most widely used conceptual model is the ER model.
ADVANTAGES
OF CONCEPTUAL MODEL
1.
It provides a
relatively easily understood birds-eye view of the data environment.
2.
It is independent
of both software and hardware.
SOFTWARE INDEPENDENCE: Means that the model does not depend on the DBMS
software used to implement the model.
HARDWARE INDEPENDENCE: Means that the model does not depend on the hardware
used in implementation of the model.
MANAGING THE DATABASE SYSTEM: A shift in focus. The role of the human component
changes from an emphasis on programming to a focus on the broader aspects of
managing the organization’s data resources and on the administration of the
complex database software itself.
THE PHYSICAL MODEL
The
physical model operates at the lowest level of abstraction, describing the way
data are saved on storage media such as disk or tapes. The precision required
in the physical model’s definition demands that database designers who work at
this level have a detailed knowledge of the hardware and software used to
implement the database design. The physical model is dependent on the DBMS,
methods of accessing files, and types of hardware storage devices supported by
the operating system. If you change the physical model without affecting the
internal model, you have physical independence.
CONCLUSION
DBMS functions:
A
DBMS performs several important functions that guarantee the integrity and
consistency of the data in the database. And the most of those functions are
transparent to end users and most can be achieved only through the use of a
DBMS. These include data dictionary management, data storage management,
security management, multi-user access control, backup and recovery management,
data integrity management, database access languages and application
programming interfaces and database communication interfaces.
EACH OF THESE FUNCTIONS IS
EXPLAINED
1.
Data dictionary
management: The DBMS stores definitions of the data elements and their
relationship in a data dictionary. Any changes made in a database structure are
automatically recorded in the data dictionary,
Data storage management: The DBMS creates and manages
the complex structures required for data st