Database Systems:
Design, Implementation, and
Management
Ninth Edition
Chapter 4
Entity Relationship (ER) Modeling
Database Systems, 9th Edition 2
Objectives
• In this chapter, students will learn:
– The main characteristics of entity re...
Database Systems, 9th Edition 3
The Entity Relationship Model (ERM)
• ER model forms the basis of an ER diagram
• ERD repr...
Database Systems, 9th Edition 4
Entities
• Refers to entity set and not to single entity
occurrence
• Corresponds to table...
Database Systems, 9th Edition 5
Attributes
• Characteristics of entities
• Chen notation: attributes represented by ovals
...
Database Systems, 9th Edition 6
Database Systems, 9th Edition 7
Attributes (cont’d.)
• Required attribute: must have a value
• Optional attribute: may be ...
Database Systems, 9th Edition 8
Database Systems, 9th Edition 9
Attributes (cont’d.)
• Composite attribute can be subdivided
• Simple attribute cannot be ...
Database Systems, 9th Edition 10
Database Systems, 9th Edition 11
Attributes (cont’d.)
• M:N relationships and multivalued attributes should
not be impleme...
Database Systems, 9th Edition 12
Database Systems, 9th Edition 13
Relationships
• Association between entities
• Participants are entities that participate...
Database Systems, 9th Edition 14
Connectivity and Cardinality
• Connectivity
– Describes the relationship classification
•...
Database Systems, 9th Edition 15
Database Systems, 9th Edition 16
Existence Dependence
• Existence dependence
– Entity exists in database only when it is
a...
Database Systems, 9th Edition 17
Relationship Strength
• Weak (non-identifying) relationships
– Exists if PK of related en...
Database Systems, 9th Edition 18
Database Systems, 9th Edition 19
Database Systems, 9th Edition 20
Weak Entities
• Weak entity meets two conditions
– Existence-dependent
– Primary key part...
Database Systems, 9th Edition 21
Database Systems, 9th Edition 22
Database Systems, 9th Edition 23
Relationship Participation
• Optional participation
– One entity occurrence does not requ...
Database Systems, 9th Edition 24
Database Systems, 9th Edition 25
Database Systems, 9th Edition 26
Relationship Degree
• Indicates number of entities or participants
associated with a rela...
Database Systems, 9th Edition 27
Database Systems, 9th Edition 28
Database Systems, 9th Edition 29
Recursive Relationships
• Relationship can exist between occurrences of
the same entity s...
Database Systems, 9th Edition 30
Database Systems, 9th Edition 31
Database Systems, 9th Edition 32
Associative (Composite) Entities
• Also known as bridge entities
• Used to implement M:N ...
Database Systems, 9th Edition 33
Database Systems, 9th Edition 34
Database Systems, 9th Edition 35
Developing an ER Diagram
• Database design is an iterative process
– Create detailed narr...
Database Systems, 9th Edition 36
Database Systems, 9th Edition 37
Database Systems, 9th Edition 38
Database Systems, 9th Edition 39
Database Systems, 9th Edition 40
Database Systems, 9th Edition 41
Database Systems, 9th Edition 42
Database Systems, 9th Edition 43
Database Systems, 9th Edition 44
Database Systems, 9th Edition 45
Database Systems, 9th Edition 46
Database Systems, 9th Edition 47
Database Design Challenges:
Conflicting Goals
• Database designers must make design
compr...
Database Systems, 9th Edition 48
Database Systems, 9th Edition 49
Summary
• Entity relationship (ER) model
– Uses ERD to represent conceptual database as
v...
Database Systems, 9th Edition 50
Summary (cont’d.)
• Connectivities and cardinalities are based on
business rules
• M:N re...
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Fundamentals of Database ppt ch04

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  1. 1. Database Systems: Design, Implementation, and Management Ninth Edition Chapter 4 Entity Relationship (ER) Modeling
  2. 2. Database Systems, 9th Edition 2 Objectives • In this chapter, students will learn: – The main characteristics of entity relationship components – How relationships between entities are defined, refined, and 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
  3. 3. Database Systems, 9th Edition 3 The Entity Relationship Model (ERM) • 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
  4. 4. Database Systems, 9th Edition 4 Entities • Refers to entity set and not to single entity occurrence • Corresponds to table and not to row in relational environment • In Chen and Crow’s Foot models, entity is represented by rectangle with entity’s name • Entity name, a noun, written in capital letters
  5. 5. Database Systems, 9th Edition 5 Attributes • Characteristics of entities • Chen notation: attributes represented by ovals connected to entity rectangle with a line – Each oval contains the name of attribute it represents • Crow’s Foot notation: attributes written in attribute box below entity rectangle
  6. 6. Database Systems, 9th Edition 6
  7. 7. Database Systems, 9th Edition 7 Attributes (cont’d.) • Required attribute: must have a value • Optional attribute: may be left empty • Domain: set of possible values for an attribute – Attributes may share a domain • Identifiers: one or more attributes that uniquely identify each entity instance • Composite identifier: primary key composed of more than one attribute
  8. 8. Database Systems, 9th Edition 8
  9. 9. Database Systems, 9th Edition 9 Attributes (cont’d.) • Composite attribute can be subdivided • Simple attribute cannot be subdivided • Single-value attribute can have only a single value • Multivalued attributes can have many values
  10. 10. Database Systems, 9th Edition 10
  11. 11. Database Systems, 9th Edition 11 Attributes (cont’d.) • M:N relationships and multivalued attributes should not be implemented – Create several new attributes for each of the original multivalued attributes’ components – Create new entity composed of original multivalued attributes’ components • Derived attribute: value may be calculated from other attributes – Need not be physically stored within database
  12. 12. Database Systems, 9th Edition 12
  13. 13. Database Systems, 9th Edition 13 Relationships • Association between entities • Participants are entities that participate in a relationship • Relationships between entities always operate in both directions • Relationship can be classified as 1:M • Relationship classification is difficult to establish if only one side of the relationship is known
  14. 14. Database Systems, 9th Edition 14 Connectivity and Cardinality • Connectivity – Describes the relationship classification • Cardinality – Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity • Established by very concise statements known as business rules
  15. 15. Database Systems, 9th Edition 15
  16. 16. Database Systems, 9th Edition 16 Existence Dependence • Existence dependence – Entity exists in database only when it is associated with another related entity occurrence • Existence independence – Entity can exist apart from one or more related entities – Sometimes such an entity is referred to as a strong or regular entity
  17. 17. Database Systems, 9th Edition 17 Relationship Strength • Weak (non-identifying) relationships – Exists if PK of related entity does not contain PK component of parent entity • Strong (identifying) relationships – Exists when PK of related entity contains PK component of parent entity
  18. 18. Database Systems, 9th Edition 18
  19. 19. Database Systems, 9th Edition 19
  20. 20. Database Systems, 9th Edition 20 Weak Entities • Weak entity meets two conditions – Existence-dependent – Primary key partially or totally derived from parent entity in relationship • Database designer determines whether an entity is weak based on business rules
  21. 21. Database Systems, 9th Edition 21
  22. 22. Database Systems, 9th Edition 22
  23. 23. Database Systems, 9th Edition 23 Relationship Participation • Optional participation – One entity occurrence does not require corresponding entity occurrence in particular relationship • Mandatory participation – One entity occurrence requires corresponding entity occurrence in particular relationship
  24. 24. Database Systems, 9th Edition 24
  25. 25. Database Systems, 9th Edition 25
  26. 26. Database Systems, 9th Edition 26 Relationship Degree • Indicates number of entities or participants associated with a relationship • Unary relationship – Association is maintained within single entity • Binary relationship – Two entities are associated • Ternary relationship – Three entities are associated
  27. 27. Database Systems, 9th Edition 27
  28. 28. Database Systems, 9th Edition 28
  29. 29. Database Systems, 9th Edition 29 Recursive Relationships • Relationship can exist between occurrences of the same entity set – Naturally found within unary relationship
  30. 30. Database Systems, 9th Edition 30
  31. 31. Database Systems, 9th Edition 31
  32. 32. Database Systems, 9th Edition 32 Associative (Composite) Entities • Also known as bridge entities • Used to implement M:N relationships • Composed of primary keys of each of the entities to be connected • May also contain additional attributes that play no role in connective process
  33. 33. Database Systems, 9th Edition 33
  34. 34. Database Systems, 9th Edition 34
  35. 35. Database Systems, 9th Edition 35 Developing an ER Diagram • Database design is an iterative process – Create detailed narrative of organization’s description of operations – Identify business rules based on description of operations – Identify main entities and relationships from business rules – Develop initial ERD – Identify attributes and primary keys that adequately describe entities – Revise and review ERD
  36. 36. Database Systems, 9th Edition 36
  37. 37. Database Systems, 9th Edition 37
  38. 38. Database Systems, 9th Edition 38
  39. 39. Database Systems, 9th Edition 39
  40. 40. Database Systems, 9th Edition 40
  41. 41. Database Systems, 9th Edition 41
  42. 42. Database Systems, 9th Edition 42
  43. 43. Database Systems, 9th Edition 43
  44. 44. Database Systems, 9th Edition 44
  45. 45. Database Systems, 9th Edition 45
  46. 46. Database Systems, 9th Edition 46
  47. 47. Database Systems, 9th Edition 47 Database Design Challenges: Conflicting Goals • Database designers must make design compromises – Conflicting goals: design standards, processing speed, information requirements • Important to meet logical requirements and design conventions • Design is of little value unless it delivers all specified query and reporting requirements • Some design and implementation problems do not yield “clean” solutions
  48. 48. Database Systems, 9th Edition 48
  49. 49. Database Systems, 9th Edition 49 Summary • Entity relationship (ER) model – Uses ERD to represent conceptual database as viewed by end user – ERM’s main components: • Entities • Relationships • Attributes – Includes connectivity and cardinality notations
  50. 50. Database Systems, 9th Edition 50 Summary (cont’d.) • Connectivities and cardinalities are based on business rules • M:N relationship is valid at conceptual level – Must be mapped to a set of 1:M relationships • ERDs may be based on many different ERMs • UML class diagrams are used to represent the static data structures in a data model • Database designers are often forced to make design compromises
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