1. Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 4 Data Modeling Using the Entity- Relationship (ER) Model Hour1 Presented & Modified by Mahmoud Rafeek Alfarra Lecturer in CST Kan younis

2. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Chapter 4 Outline  Using High-Level Conceptual Data Models for Database Design  A Sample Database Application  Entity Types, Entity Sets, Attributes, and Keys  Relationship Types, Relationship Sets, Roles, and Structural Constraints  Weak Entity Types

3. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Chapter 4 Outline (cont’d.)  Refining the ER Design for the COMPANY Database  ER Diagrams, Naming Conventions, and Design Issues  Example of Other Notation: UML Class Diagrams  Relationship Types of Degree Higher than Two

4. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Entity-Relationship (ER) Model  Entity-Relationship (ER) model  Popular high-level conceptual data model  ER diagrams  Diagrammatic notation associated with the ER model  Unified Modeling Language (UML)

5. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Using High-Level Conceptual Data Models for Database Design  Requirements collection and analysis  Database designers interview prospective database users to understand and document data requirements  Result: data requirements  Functional requirements of the application

6. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Entity Types, Entity Sets, Attributes  ER model describes data as:  Entities  Relationships  Attributes

7. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Entities and Attributes  Entity  Thing in real world with independent existence  Attributes  Particular properties that describe entity  Types of attributes: Composite versus simple (atomic) attributes Single-valued versus multivalued attributes Stored versus derived attributes NULL values Complex attributes

8. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 ER Diagrams, Naming Conventions, and Design Issues

9. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Types of attributes  A composite attribute An attribute broken into component parts

10. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Types of attributes  Simple key attribute The key is underlined

11. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Types of attributes  Composite key attribute The key is composed of two subparts

12. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Types of attributes multivalued derived  Entity with a multivalued attribute (Skill) and derived attribute (Years_Employed) Derived from date employed and current date Multivalued: an employee can have more than one skill

13. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Types of attributes  An attribute that is both multivalued and composite This is an example of time-stamping

14. Copyright © 2011 Ramez Elmasri and Shamkant Navathe Entities and Attributes

15. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 و ذكـِّر عَنْ أَبِي الدَّرْدَاءِ رضي الله عنه، قَالَ : " إِنَّمَا الْعِلْمُ بِالتَّعَلُّمِ ، وَإِنَّمَا الْحِلْمُ بِالتَّحَلُّمِ ، وَمَنْ يَتَوَخَّ الْخَيْرَ يُعْطَهُ ، وَمَنْ يَتَوَقَّ الشَّرَّ يُوقَهُ ". موقوف

16. Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 4 Data Modeling Using the Entity- Relationship (ER) Model Hour2 Presented & Modified by Mahmoud Rafeek Alfarra Lecturer in CST Kan younis

17. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Entity Types, Entity Sets and Value Sets  Entity type  Collection (or set) of entities that have the same attributes (often corresponds to a table)

18. Copyright © 2011 Ramez Elmasri and Shamkant Navathe Initial Conceptual Design of the COMPANY Database

19. Copyright © 2011 Ramez Elmasri and Shamkant Navathe Initial Conceptual Design of the COMPANY Database

20. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Relationship Types, Relationship Sets, Roles, and Structural Constraints  Relationship  When an attribute of one entity type refers to another entity type  Represent references as relationships not attributes

21. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Relationship Types, Sets, and Instances  The relationship type is modeled as the diamond and lines between entity type.  The instance is between specific entity instances.

22. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Relationship Degree  Degree of a relationship type  Number of participating entity types  Unary, Binary, ternary  Relationships as attributes  Think of a binary relationship type in terms of attributes

23. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Relationship Degree One entity related to another of the same entity type Entities of two different types related to each other Entities of three different types related to each other

24. Copyright © 2011 Ramez Elmasri and Shamkant Navathe Ternary

25. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011

26. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 و ذكـِّر عن أبي عبد الرحمن معاذ بِن جبل رضي الله عنهما : عن رسول الله صلى الله عليه وسلم قال : ( اتق الله حيثما كنت، وأتبع السيئة الحسنة تمحها ، وخالق الناس بخلق حسن ). حديث حسن.

27. Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 4 Data Modeling Using the Entity- Relationship (ER) Model Hour3 Presented & Modified by Mahmoud Rafeek Alfarra Lecturer in CST Kan younis

28. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships One-to-One  One-to-One  Each entity in the relationship will have exactly one related entity  One-to-Many  An entity on one side of the relationship can have many related entities, but an entity on the other side will have a maximum of one related entity  Many-to-Many  Entities on both sides of the relationship can have many related entities on the other side

29. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships  Cardinality Constraints - the number of instances of one entity that can or must be associated with each instance of another entity.  Minimum Cardinality  If zero, then optional.  If one or more, then mandatory.  Maximum Cardinality  The maximum number.

30. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships

31. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships

32. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships Note: a relationship can have attributes of its own

33. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships Basic relationship with only maximum cardinalities showing

34. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships Mandatory minimum cardinalities

35. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships

36. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships Here, the date completed attribute pertains specifically to the employee’s completion of a course…it is an attribute of the relationship A binary relationship with an attribute

37. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships A unary relationship with an attribute. This has a many- to-many relationship

38. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Cardinality of Relationships Entities can be related to one another in more than one way

39. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Weak Entity Types  Do not have key attributes of their own  Identified by being related to specific entities from another entity type  Identifying relationship  Relates a weak entity type to its owner  Always has a total participation constraint

40. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Refining the ER Design for the COMPANY Database  Change attributes that represent relationships into relationship types  Determine cardinality ratio and participation constraint of each relationship type

41. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 A Sample Database Application  COMPANY  Employees, departments, and projects  Company is organized into departments  Department controls a number of projects  Employee: store each employee’s name, Social Security number, address, salary, gender, and birth date  Keep track of the dependents of each employee

42. Copyright © 2011 Ramez Elmasri and Shamkant Navathe

44. modified by Mahmoud Rafeek Alfarra, April 2011 Example of Other Notation: UML Class Diagrams  UML methodology  Used extensively in software design  Many types of diagrams for various software design purposes  UML class diagrams  Entity in ER corresponds to an object in UML Case Study Next Sunday 17 April

45. Copyright © 2011 Ramez Elmasri and Shamkant Navathe

46. modified by Mahmoud Rafeek Alfarra, April 2011 Example of Other Notation: UML Class Diagrams  Class includes three sections:  Top section gives the class name  Middle section includes the attributes;  Last section includes operations that can be applied to individual objects

47. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Example of Other Notation: UML Class Diagrams  Associations: relationship types  Relationship instances: links  Binary association  Represented as a line connecting participating classes  May optionally have a name  Link attribute  Placed in a box connected to the association’s line by a dashed line

48. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Example of Other Notation: UML Class Diagrams  Multiplicities: min..max, asterisk (*) indicates no maximum limit on participation  Types of relationships: association and aggregation  Distinguish between unidirectional and bidirectional associations  Model weak entities using qualified association

49. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 Summary  Basic ER model concepts of entities and their attributes  Different types of attributes  Structural constraints on relationships  ER diagrams represent E-R schemas  UML class diagrams relate to ER modeling concepts

50. Copyright © 2011 Ramez Elmasri and Shamkant Navathe modified by Mahmoud Rafeek Alfarra, April 2011 و ذكـِّر قال الله تعالى: ( وَلَقَدْ وَصَّيْنَا الَّذِينَ أُوتُوا الْكِتَابَ مِنْ قَبْلِكُمْ وَإِيَّاكُمْ أَنِ اتَّقُوا اللَّهَ ) ( النساء : من الآية 131)