1. CS34311 The Entity- Relationship Model Part II.

2. CS34312 Database Design Stages Application Requirements Conceptual Design Logical Design Physical Design Conceptual Schema Logical Schema Physical Schema

3. CS34313 Relationship types in ER Model 3-ary “supplies” relationship: Supplier supplies Products to Consumers

4. CS34314 Recursive Relationship Types and Roles Recursive relationship type : Part-Subpart Roles: There are Parts that play the role of superPart There are Parts that play the role of subPart

5. CS34315 ER Model so far Structures Entity Types Relationship Types Binary, ternary, n-ary Recursive Attributes For entity types and relationship types Simple, composite, multivalued Roles

6. CS34316 ER Model: Key Constraints How : Underline the key attribute/attributes Key for Student is sNumber Key for Movie is Note: We can represent key for entity type consisting of more than 1 attribute (e.g.: Movie) We cannot represent multiple keys for an entity type (e.g: key for Student can be either sNumber or sName)

7. CS34317 ER Model: Cardinality Constraints How : Expressed using (min, max) Student can take >= 2 and <= 3 Courses Course can have >= 0 and <= * (infinity) Students min and max are non-negative integers max > min

8. CS34318 Cardinality Constraints 1:1 relationship type: A Dept has exactly one Manager, A Person can manage at most one Dept Person pNumber pName Dept dNumber dName Manages

9. CS34319 Cardinality Constraints 1:1 relationship type: A Dept has exactly one Manager, A Person can manage at most one Dept

10. CS343110 Cardinality Constraints 1:1 relationship type: A Dept has exactly one Manager, A Person can manage at most one Dept

11. CS343111 Cardinality Constraints 1:many relationship type: A Person works for exactly one Dept, A Dept can have any number of Persons Person pNumber pName Dept dNumber dName Works For

12. CS343112 Cardinality Constraints 1:many relationship type: A Person works for exactly one Dept, A Dept can have any number of Persons

13. CS343113 Cardinality Constraints 1:1 relationship type: A Dept has exactly one Manager, A Person can manage at most one Dept 1:many (1:n) relationship type: A Person works for exactly one Dept, A Dept can have any number of Persons Person pNumber pName Dept dNumber dName Manages (0, 1)(1, 1) Person pNumber pName Dept dNumber dName Works For (1, 1)(0, *)

14. CS343114 Cardinality Constraints 1:1 relationship type: A Dept has exactly one Manager, A Person can manage at most one Dept 1:many (1:n) relationship type: A Person works for exactly one Dept, A Dept can have any number of Persons

15. CS343115 Cardinality Constraints many:many (m:n) relationship type: A Person works for one or more Depts, A Dept can have any number of Persons Person pNumber pName Dept dNumber dName Works For

16. CS343116 Cardinality Constraints many:many (m:n) relationship type: A Person works for one or more Depts, A Dept can have any number of Persons

17. CS343117 Cardinality Constraints for n-ary relationships A Supplier supplies at least one Product to some Consumer Supplier sName sLoc Consumer cName cLoc Supply price Product pName pNumber qty

18. CS343118 Cardinality Constraints for n-ary relationships A Supplier supplies at least one Product to some Consumer

19. CS343119 Cardinality Constraints for n-ary relationships What about the following constraints : (1) A Consumer gets a Product from only one Supplier (2) Each Supplier supplies exactly 2 Products

20. CS343120 Cardinality Constraints for Recursive Relationships A Part can be subpart of one superPart A Part can have many subParts Contains Part pName pNumber subPartsuperPart quantity

21. CS343121 Cardinality Constraints for Recursive Relationships A Part can be subpart of one superPart A Part can have many subParts

22. CS343122 Cardinality Constraints for Recursive Relationships A Part can be subpart of one superPart A Part can have many subParts A Part can be subpart of many superParts A Part can have many subParts

23. CS343123 Cardinality Constraints for Recursive Relationships A Part can be subpart of one superPart A Part can have many subParts A Part can be subpart of many superParts A Part can have many subParts

24. CS343124 ER Model Constraints Summary Key Constraints Cardinality Constraints Expressed using (min, max) Binary relationship types are called 1:1, 1:many, many:many

25. CS343125 Summary of ER Structures Entity Types Relationship types – binary, ternary, n-ary. recursive Attributes For entity types or relationship types Simple, composite or multi-valued Constraints – key, cardinality Roles of entity types in a relationship type ISA relationship types Weak Entity Types – identifying relationship type, identifying entity type