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Relational Databases - Lecture 2 - Entity-relationship diagram
The document describes the key concepts of an entity-relationship diagram (ERD), which is a conceptual model used to design databases. It defines entities (objects), attributes (characteristics of entities), and relationships (associations between entities). The document provides examples of common entities like students and universities, and relationships like students attending universities. It also covers attribute types, cardinalities, and notations for drawing ERDs.
Relational Databases - Lecture 2 - Entity-relationship diagram
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- 2. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 ED diagram Chen's notationproposed in 1976 Entity Relationship Entity Entity Attribute Relationship Attribute Attribute Attribute Attribute Attribute Attribute Attribute Attribute Attribute
- 3. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Entity Student University Employee Department Would become arelation • Categories of similar measurements • Could be a physical object or a concept
- 4. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Attributes • Measurements withina category Student Name Surname Nationality StudentID Name StudentID Surname Nationality Student
- 5. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Attributes • Atomic vs.Composite Student Name StudentID Surname Nationality ( Address ) City Zip Country ( Street ) Name Number
- 6. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Attributes • Single vs.Multi-valued Student Name StudentID Surname Nationality { Degree } University Year Title
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- 12. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Cardinality • One-to-one • One-to-many •Many-to-one • Many-to-many Person Carowns 1 1 Person Carowns 1 N Student Universit y attends N 1 Student Classattends N N
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- 17. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Primary key • Uniquenon-null identifier attribute for a tuple Student Name Surname Nationality StudentID 27643 9345 6523 1984 Name StudentID Surname Nationality Student
- 18. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Composite key ClassRoom DescsNumber ( ClassroomID) RoomNumber Building RoomNumber Building DescsNumber 101 T 101 N 102 A 102 B
- 19. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Foreign key • Uniqueidentifier that enforces a link between the data in two tables Student Name StudentID Surname Nationality University Name Address Country Attends
- 20. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Foreign key • Uniqueidentifier that enforces a link between the data in two tables Student UniversityAttends StudentID Name Surname Nationality University.Name
- 21. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Weak entity Color BuildingID NumFloors Height Number Floor Size Buildingcontains Apartmentcontains • Primary key contains foreign key
- 22. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Weak entity Building containsApartmentcontains • Primary key contains foreign key Building.BuildingID Number Size Floor
- 23. 1 0 1 0 0 1 0 1 0 1 0 0 1 0 1 0 0 1 0 0 1 0 ✐ ✐ ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ ✐ ✑ ✐ ✑ ✑ 1 1 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 1 0 1 1 ✑ ✐ ✑ ✐ ✐ ✑ ✑ ✐ ✐ ✑ ✐ 1 1 1 0 0 1 0 1 0 0 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 0 0 1 ✑ ✑ 1 ✑ ✑ 1 0 1 Many-to-many • Cannot existin the database • Must be split with a weak entity Student ClassAttends StudentID ClassID
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