extended modelling in dbms using different.pptx

Organization of this Chapter:
• Introduction
• Superclasses and Subclasses
• Specialization and Generalization
• Constraints on specialization/generalization
• Aggregation and Composition
• Sample example
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Enhanced ER Model
• The Enhanced ER model, EER model, includes all the
modeling concepts of ER model along with some additional
concepts like super class and sub class, specialization,
generalization, aggregation, and composition.
• Super class and Sub class:
– Super class is an entity type that has a relationship with one
or more subtypes. On the other hand, Sub class is a group
of entities with unique attributes.
– Sub class inherits properties and attributes from its super
class. Sub class and Super class relationship leads the
concept of Inheritance.
– The relationship between sub class and super class is
denoted with d symbol, where d means disjointness.
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Specialization and Generalization
• Specialization
– The process of designating sub groupings within
an entity set is called Specialization.
– An entity set may be specialized by more than one
distinguishing features.
– ER-design, specialization is depicted by an
Inverted Triangle component labeled “IS A” (is a).
– Specialization can be repeatedly used to refine a
ER design.
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Generalization
• Generalization is the process of combining similar entities into a
more generalized entity.
• It allows for the abstraction of common properties and relationships
shared by multiple entities into a single higher-level entity. This
process moves from specific to general.
• Purpose: Simplifies the data model by grouping common features
into a generalized (parent) entity, avoiding redundancy.
• Hierarchy: Generalization forms a bottom-up hierarchy, where
several lower-level entities are abstracted into a higher-level
generalized entity.
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EER Model (contd..)
• Generalization:
– Generalization is a simple inversion of specialization. It is
the process of extracting common properties from a set of
entity types and creating a generalized entity type from it.
– It is a bottom-up approach in which two or more entitiy
types can be generalized to a higher level entity type, if
they have some attributes in common.
– Specialization adopts top-down approach, while
Generalization adopts bottom-up approach.
– A crucial property of the higher-level and lower-level
entities created by specialization and generalization is
attribute inheritance.
– A lower-level entity set (or subclass) also inherits
participation in the relationship sets in which its higher-
level entity (or superclass) participates
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• Construct an ER diagram for the following:
• “A university maintains record of students
and the programmes in which they have
enrolled. It stores the student name, id ,
phone no, address of student and
programme code ,programme name and
duration. A student is either full time or part
time student(only one of the types). A
student can register for multiple
prgrammmes and vice versa.”
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Steps to draw ER diagram
• An Entity-Relationship (ER) diagram is used to
visually represent the structure of a database. It
shows entities, relationships, and the attributes
that describe them. Here’s a step-by-step guide
to draw an ER diagram:
• Identify Entities
• Entities are objects or concepts about which
data is stored. These could be things like
"Customer," "Order," or "Product."
• Entities are typically represented by rectangles.
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• Identify Relationships
• A relationship is a connection between two or
more entities. For example, a "Customer" can
"Place" an "Order."
• Relationships are shown using diamonds or
lines connecting entities.
• Example:
• "Customer" places "Order" (relationship: places)

• Determine the Cardinality of Relationships
• Cardinality defines how entities relate to each other (e.g.,
one-to-one, one-to-many, many-to-many).
• Use notations like "1" or "M" to specify cardinality. For
example, one customer can place many orders (1 to M
relationship).
• Example:
• 1 Customer places M Orders

• Add Attributes
• Attributes provide more details about each entity (e.g.,
"Customer Name," "Order Date").
• Attributes are represented by ovals connected to their
respective entity rectangles.
• Example:
• Attributes of "Customer": CustomerID, CustomerName,
Email
• Attributes of "Order": OrderID, OrderDate, TotalAmount

• Identify Primary Keys
• Each entity should have a primary key, a unique identifier
for each record in that entity
• Define Foreign Keys (if any)
• Foreign keys establish links between related entities. For
example, "Order" might have a foreign key "CustomerID"
that links it back to the "Customer" entity.
• Example:
• The "Order" entity could have a "CustomerID" attribute,
which is a foreign key from the "Customer" entity.

• Normalize the Diagram (Optional)
• Review your diagram to ensure that there
is no redundancy or unnecessary
relationships.
• Normalize the design to avoid data
duplication.

Constraints in Generalization:
• Loss of Specificity: By generalizing, you may lose
some specific characteristics of individual entities in the
higher-level abstraction
• Design Complexity: While generalization reduces
redundancy, it may increase the complexity of
relationships and hierarchy in the database schema.
• .

Constraints on Generalization/Specialization
• Membership Constraint
– Condition defined/Attribute defined
• All the lower level entity is identified on the basis of same type of
attribute this type of generalization is said to be attribute defined.
– Here the lower level entity is generalized on the basis
of accnt type.
Accnt no Accnt name Branch Accnt type
005 a1 Ambala Saving a
008 a2 chandigarh Current a
009 a3 mohali Saving a

– User-defined
• User-defined lower-level entity sets are not constrained by a
membership condition; rather, the database user assigns entities to a
given entity set.
• EX: A celebrity can be personalised into actor and politician.
• Disjoint constraints
– Disjoint:
• The disjoint constraint only applies when a superclass has more
than one subclass. If the subclasses are disjoint, then an entity
occurrence can be a member of only one of the subclasses .e.g.
postgrads or undergrads; one cannot be both.
• To represent a disjoint superclass/subclass relationship, Or is used.

contd..
• Overlapping: This applies when an entity occurrence may be a
member of more than one subclass, e.g. student and staff; some
people are both. And is used to represent the overlapping
specialization/generalization relationship in the ER diagram.

contd..
• Completeness constraints
– Total: Each superclass (higher-level entity) must belong to
subclasses (lower-level entity sets), e.g. a student must be
postgrad or undergrad. To represent completeness in the
specialization/generalization relationship, the keyword
Mandatory is used.

contd..
• Partial: Some superclasses may not belong to subclasses
(lower-level entity sets), e.g. some people at UCT are neither
student nor staff. The keyword Optional is used to represent a
partial specialization/generalization relationship.

Aggregation and Composition
• Aggregation:
– Aggregation represents a has-a relationship between entity types,
where one represents the whole and the other the part.
– An example of aggregation is the Car and Engine entities. A car is
made up of an engine. The car is the whole and the engine is the part.
– Aggregation does not represent strong ownership. This means, a part
can exist on its own without the whole. There is no stronger ownership
between a car and the engine. An engine of a car can be moved to
another car.
– A line with a diamond at the end is used to represent aggregation.The
whole must be put at the end of the diamond.

contd..
• Composition
– Composition is a form of aggregation that represents an
association between entities, where there is a strong
ownership between the whole and the part.
– For example,: a tree and a branch have a composition
relationship. A branch is 'part' of a 'whole' tree - we cannot
cut the branch and add it to another tree.
– A line with a filled diamond at the end is used to represent
composition where the diamond side is towards the part
side.

An Example

extended modelling in dbms using different.pptx

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