Data Model & Classification of Data Models
https://www.computersprofessor.com/2016/04/data-model-and-classification-of-data-models.html
DEFINITION:
A data model is an abstraction of reality. The reality may be a
business system or an engineering system.
DATA MODEL:
Data model is an abstraction of data about entities of a system
.The structure of the data base system is the concept of data model .Thus, it
is a collection of conceptual tools for describing data, data relationships, data
semantics & constraints. Therefore, a data model is relatively simple
representation within the database environment.
For the conceptual data model, We define an entity relationship
model which is known as ER-Diagram. It
is a special form of network data model in which we use certain symbols to indicate the name of the
associations between the meaningful pairs of relations in the conceptual model.
The importance of ER-DIAGRAM is that, they help the database designer to have a better insight of the model. This will in turn, help the database designer to implement the conceptual data model into any one of the following data models.
1. HIERARCHIAL DATA MODEL (HDM)
2. NETWORK DATA MODEL (NDM)
3. RELATIONAL DATA MODEL (RDM)
We use ellipses to indicate the fields of
a relational table and use a rectangular box to specify the table and its relationship
around the relation.
The associations
between the fields of a file can be categorized into,
A)
one-to-one association(1:1<->)
B)
one-to-one association(1:M<->)
C)
Many- to Many association(M:M<->)
D)
Many-to –one association(M:1<->)
E) one-to-one conditional association(<-0->)
CLASSIFICATIONS OF DATA MODELS:
The data models are classified into 4 types
1) External View or Users view
2)
Conceptual Data Model
3) Internal
Data Model
4)
Physical Data Model
The arrangement of all the files for an
entire organization is called schema.
The schema defines a schematic representation or over all view of all the files
in a database. A portion of the schema of a database is called sub- schema.
In database environment, the data models
are discussed on the basis of their degree of abstraction.
1. EXTERNAL VIEW OR USER VIEW
The
different sub-schemas of the data base is called as user view or external view.
For example, a production, planning, stores department, quality control, maintenance
schedule etc, are sub schemas of a production system. Similarly funds flow
analysis, breakeven analysis, costing, payroll, materials account etc are the
sub-systems of a Finance System.
2. CONCEPTUAL
DATA MODEL
It
is a overall or consolidated view of all the user views. It gives a
comprehensive view of the entire data base. The conceptual data model that
represents global view of the data. This model is the basis for identification
& description of main data avoiding details. The most widely used
conceptual data model in database environment is, ER-model. In conceptual data
model, the details either in hardware or software will have no effect on the
data base design at the conceptual level.
3. INTERNAL
DATA MODEL
After
planning the conceptual data model, it is mapped or implemented into any one of
the data models such as HDM, NDM or RDM. Then, it is called as Internal Data Model.
The internal data model requires the
database designer to match the conceptual data model characteristics & the
other constraints to the above 3 data models. Thus, the internal data model
depends on the existence of a specific database software.
4. PHYSICAL
DATA MODEL
The
physical data model operates at the lowest level of abstraction, describing the
way the data stored or saved on the
storage media such as hard disc, magnetic tapes etc.
The physical data model is derived from
the internal data model after incorporating certain methods and defining all
storage specifications.