Database Systems: Design, Implementation, and Management Tenth Edition
description
Transcript of Database Systems: Design, Implementation, and Management Tenth Edition
![Page 1: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/1.jpg)
Database Systems: Design, Implementation, and
ManagementTenth Edition
Chapter 4Entity Relationship (ER) Modeling
![Page 2: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/2.jpg)
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
Database Systems, 10th Edition 2
![Page 3: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/3.jpg)
Database Systems, 10th Edition 3
![Page 4: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/4.jpg)
Derived Attributes
• Derived attribute: value may be calculated from other attributes– Need not be physically stored within database
Database Systems, 10th Edition 4
![Page 5: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/5.jpg)
Database Systems, 10th Edition 5
![Page 6: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/6.jpg)
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
Database Systems, 10th Edition 6
![Page 7: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/7.jpg)
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
Database Systems, 10th Edition 7
![Page 8: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/8.jpg)
Database Systems, 10th Edition 8
![Page 9: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/9.jpg)
Database Systems, 10th Edition 9
![Page 10: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/10.jpg)
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
Database Systems, 10th Edition 10
![Page 11: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/11.jpg)
Database Systems, 10th Edition 11
![Page 12: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/12.jpg)
Database Systems, 10th Edition 12
![Page 13: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/13.jpg)
Recursive Relationships
• Relationship can exist between occurrences of the same entity set
Database Systems, 10th Edition 13
![Page 14: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/14.jpg)
Recursive Relationships• Relationship can exist between occurrences of
the same entity set
Database Systems, 10th Edition 14
![Page 15: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/15.jpg)
Recursive Relationships
Database Systems, 10th Edition 15
![Page 16: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/16.jpg)
Database Systems, 10th Edition 16
![Page 17: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/17.jpg)
1:1 Recursive Relationship Implementation• EMPLOYEE_V1 table can yield anomalies if Anne Jones
divorces Anton Shapiro– Two records must be updated, if only one is updated then we
have inconsistent data
– Nulls for those employees not married to other employees
• MARRIED_V1 eliminates nulls for employees not married to other employees but duplicate values are still possible (345,347) and (347,345)
• Third method requires collection of marriage date. Unless sending out congratulations each year, the information is unnecessary
• Theoretically possible to have more than two people in a marriage
Database Systems, 10th Edition 17
![Page 18: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/18.jpg)
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
Database Systems, 10th Edition 18
![Page 19: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/19.jpg)
Database Systems, 10th Edition 19
![Page 20: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/20.jpg)
Database Systems, 10th Edition 20
![Page 21: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/21.jpg)
Database Systems, 10th Edition 21
![Page 22: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/22.jpg)
Database Systems, 10th Edition 22
![Page 23: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/23.jpg)
Database Systems, 10th Edition 23
![Page 24: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/24.jpg)
Database Systems, 10th Edition 24
![Page 25: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/25.jpg)
Database Systems, 10th Edition 25
![Page 26: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/26.jpg)
Database Systems, 10th Edition 26
![Page 27: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/27.jpg)
Database Systems, 10th Edition 27
![Page 28: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/28.jpg)
Database Systems, 10th Edition 28
![Page 29: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/29.jpg)
Design Challenges• Must conform to design standards
– Minimize redundancies and avoid nulls when possible
• Processing Speed– High processing speeds are a top priority in today’s online world
– Combine two tables into one which may be less elegant but faster data retrieval
– Include derived attributes instead of computing them as needed
• Information Requirements– Complex information requirements might require additional
entities and attributes within the design
– May be worth sacrificing “clean” design and speed to ensure maximum information generation
Database Systems, 10th Edition 29
![Page 30: Database Systems: Design, Implementation, and Management Tenth Edition](https://reader036.fdocuments.in/reader036/viewer/2022081603/56814667550346895db38995/html5/thumbnails/30.jpg)
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
Database Systems, 10th Edition 30