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Chapter 4
Entity Relationship (ER) Modeling
Database Systems:
Design, Implementation, and Management,
Seventh Edition, Rob and Coronel
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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In this chapter, you will learn:
• The main characteristics of entity relationship
components
• How relationships between entities are defined and
refined and how those relationships are incorporated
into the database design process
• How ERD components affect database design and
implementation
• That real-world database design often requires the
reconciliation of conflicting goals
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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The Entity Relationship (ER) Model
• ER model forms the basis of an ER diagram
• ERD represents conceptual database as
viewed by end user
• ERDs depict database’s main components:
– Entities
– Attributes
– Relationships
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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Entities
• Refers to entity set and not to single entity
occurrence
• Corresponds to table and not to row in relational
environment
• In both Chen and Crow’s Foot models, entity is
represented by rectangle containing entity’s
name
• Entity name, a noun, is usually written in capital
letters
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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Attributes
• Characteristics of entities
• In Chen model, attributes are represented by
ovals and are connected to entity rectangle with
a line
• Each oval contains the name of attribute it
represents
• In Crow’s Foot model, attributes are written in
attribute box below entity rectangle
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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Attributes (continued)
Database Systems: Design, Implementation, & Management, 7th Edition, Rob & Coronel
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Domains
• Attributes have domain
– Domain is attribute’s set of possible values
• Attributes may share a domain
Database Systems: Design, Implementation, & Manage