1. CONCEPTUAL DESIGN One of the model for conceptual schema is
ER(entity relational) model. Note : weak entity does not mean total
participation or having identifying relationship but identifying
relationship implies total participation. ENHANCED ER NOTATIONS/
ENTENDED ER NOTATIONS: An association between the subclass entity B
with another entity A is called as inheritance. In other words, an
entity class B is said to be a subclass of other class A if it
share the is a relationship with A. example, A car is aVehicle.
Here a vehicle is a more general class. A car is a vehicle but
vehicle cannot necessarily car, vehicle may be a bus, scooter or
cycle etc. An entity of class B is said to be specialization of
entities of class A. conversely, entities of A is said to be
generalizations of class B entities. So we called car as
specialization of vehicle because it is specific entity and vehicle
represents the general class of these specific entities, so we
called them generalizations of theses specialized class. A
specialized class may have more attributes than the general class
but the general class represent those attributes which are common
among the specialized classes. 2. PROPERTIES OF GENERALIZATION AND
SPECIALIZATION: 1.a subclass undergo type inheritance of the super
class. That is, each member of the subclass has the same attributes
as the super class entities and participates in the same
relationship types. 2. if a general class participates in
relationship types then the specialized class should also
participates in the same relationship types. That is if a vehicle
is said to go from point M to point N, then car or truck or cycle
should also go from point M to point N. Example : 3. Specialization
: the process of creating subclasses from the given entity type is
called specialization. Suppose in the UOD( universe of discourse)
we found found that there is a vehicle class and in the vehicle
class , we found that there are cars, trucks, scooter and cycle and
I found are theses are vehicle. So we create them as subclass of
vehicle class. Generalization : the reverse of taking two or more
entity types and clubbing them under a common super class is called
as generalization. Suppose in the UOD , we have cars, trucks,
scooters and cycles, all of these have some common attributes. So
we make them as a specialized class of more general class vehicle
which have attributes common among specialized class . It is not a
straight forward process. It depends on the application context.
PROPERTIES OF SPECIALIZED CLASS: whatever the attributes the
general class have , that attributes should also be inherited by
the specialized class. 4. Formation of the generalized class. Here
the D denotes that the subclasses are disjoint. 5. Predicate
defined class: in this the specialized class is formed on the basis
of value of attribute called predicate attribute which is here it
is called job type. Admin Academic 6. Here O denotes that the sub
class that are not disjoint are said to be overlap. Disjoint or
overlap may be partial or total. Admin Academic 7. UNION TYPES OR
CATEGORIES: an account holder an be an individual or family or
institution. Not every individual or family or institution is an
account holder. In such a case, an account holder is said to be a
partial union. Usually a constraint is specified that determines
which entity has to participates in the union. 8. Aggregation : we
called it as knowledge management. In this aggregation aggregates
the schema to a higher level of abstraction. Aggregation brings
about the contain ship. Here the aggregating entity called offers
which contains the atleast an instances of relationship between the
instructor, semester and course. The difference between the
abstraction in the inheritance and abstraction in the aggregation
is that in aggregation, the relationship show the containment
whereas in the inheritance the relationship shows the is a.
