This document discusses issues to consider when designing an entity-relationship (ER) diagram. It covers: 1. Whether to represent objects as entity sets or relationship sets. 2. Whether relationships should be binary or n-ary. N-ary relationships can be represented as multiple binary relationships connected through a new entity set. 3. Where to place attributes of relationships, which may depend on the cardinality ratio of the relationship. For example, attributes of a one-to-many relationship can be placed on the "many" side.

1. Dr. Amiya Ranjan Panda
Assistant Professor [II]
School of Computer Engineering,
Kalinga Institute of Industrial Technology (KIIT),
Deemed to be University,Odisha
ER Diagram Design Issues
KALINGA INSTITUTE OF INDUSTRIAL
TECHNOLOGY
School Of Computer
Engineering
4 Credit Lecture Note 07

2. Chapter Contents
q ER Diagram design Issues
q ER Diagram design Methodologies
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3. ER diagram design issues need to be discussed for better ER- design.
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ER Diagram Design Issues
1. Use of Entity set vs. Attributes:

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ER Diagram Design Issues…
2. Use of Entity sets vs. Relationship sets
Sometimes, an entity set can be better expressed in relationship set. Thus, it is
not always clear whether an object is best expressed by an entity set or a
relationship set.

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ER Diagram Design Issues…
3. Binary vs. n-ary relationship sets
Relationships in databases are often binary. Some relationships that appear to
be non-binary could actually be better represented by several binary
relationships.
Ø It is always possible to replace a non-binary relationship set by a number
of distinct binary relationship sets. For example, consider a ternary
relationship R associated with three entity sets A, B and C. We can replace
the relationship set R by an entity set E and create three relationship sets as:
ü RA, relating E and A
üRB , relating E and B
üRC , relating E and C
Ø If the relationship set R had any attributes, these are assigned to entity set
E. A special identifying attribute is created for E.

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ER Diagram Design Issues…
4. Placement of Relationship Attributes
The cardinality ratio of a relationship can affect the placement of relationship
attributes:
ü One-to-Many: Attributes of 1:M relationship set can be repositioned to only
the entity set on the many side of the relationship.
ü One-to-One: The relationship attribute can be associated with either one of the
participating entities.
ü Many-to-Many: Here, the relationship attributes can not be represented to the
entity sets; rather they will be represented by the entity set to be created for the
relationship set.

7. Ø The guidelines that should be followed while designing an ER diagram are
discussed below:
ü Recognize entity sets
ü Recognize relationship sets and participating entity sets
ü Recognize attributes of entity sets and attributes of relationship sets
ü Define binary relationship types and existence dependencies
ü Define general cardinality, constraints, keys, and discriminators
ü Design diagram
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ER Diagram Design Methodologies

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