Relational Databases - Lecture 2 - Entity-relationship diagram
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Conceptual model and entity-relationship diagram (Chen's notation)
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Relational Databases - Lecture 2 - Entity-relationship diagram
- 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 notation proposed 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 a relation • 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 within a 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
- 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
- 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 • Unique non-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 • Unique identifier 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 • Unique identifier 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 Building contains 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 contains Apartmentcontains • 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 exist in the database • Must be split with a weak entity Student ClassAttends StudentID ClassID
- 24. 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 Student Class Completion StudentID ClassID containsachieves containscontains Semester Grade