ITS232 Introduction To Database Management Systems

1. ITS232Introduction To Database Management Systems SitiNurbaya Ismail Faculty of Computer Science & Mathematics, UniversitiTeknologi MARA (UiTM), Kedah | sitinurbaya@kedah.uitm.edu.my | http://www.sitinur151.wordpress.com | | A2-3039 | ext:2561 | 012-7760562 | CHAPTER 4 Entity Relationship (E-R) Modeling (ERD)

2. Chapter 4: Entity Relationship (E-R) Modeling 4.0 Entity Relationship (E-R) Modeling 4.1 The Entity Relationship (ER) Model 4.2 Developing An E-R Diagram 4.3 Database Design Challenges

3. Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept A model is description or analogy used to visualize something that cannot be directly observed.

4. Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept • Relatively simple representations of complex real world data structures • A data model represents: • data structures and their characteristics • relation and constraints • Can be physical or abstract: • car, student = physical • subject, register = abstract • Used by database designer as: • communications tools to communicate and understanding between a client and the database designer, which the database to be develop.

5. Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept The importance of data modeling: • Data • constitute the most basic information units employed by a system • Application • is created to manage data and to transform data to information • View • different people views the same data differently based on their understanding • Model • helps different user to have the holistic view of the same data

6. Chapter 4: Entity Relationship (E-R) ModelingBasic Modeling Concept • Three Level ANSI-SPARC Architecture User 2 User 1 User n -user’s view External Model … View 1 View 2 View n 1. External level -designer’s view -h/w independent -s/w independent ERD Conceptual Model Conceptual Schema 2. Conceptual level -DBMS’s view -h/w independent -s/w dependent Internal Schema Internal Model 3. Internal level Database -h/w dependent -s/w dependent Physical Model Physical data organization

7. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model Based on the set theory and the relational theory, it is used as tools to: • translate different views of data among managers, users and programmers to fit into a common work • define data processing and constraints to help meet the different views • help implement the database • considered as a stage in a database design preceding/before the relational database modeling • gives data structures representation of: • what information to be stored • the relationships between informational elements and constraint on the data structure • relationship

8. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model • ER model forms the basis of an ER diagram (ERD) • ERD represents conceptual database as viewed by end user • ERDs depict/shows database’s main components: • Entities • Attributes • Relationships

9. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Entity Entity • Represents an object from the real world • Collection of similar entities that made up entity sets • Refers to entity set and not to single entity occurrence • Corresponds to table and not to row in relational environment • In both Chen and Crow’s Foot models, entity is represented by rectangle containing entity’s name • Entity name, a noun, is usually written in capital letters

10. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Attribute Attribute • Characteristics of entities • Property that explains about entity • Correspondents to fields of a table • Primary key are underline with a straight line • Foreign key are underline with dotted line or an * • Chen Model • attributes are represented by ovals and are connected to entity rectangle with a line • each oval contains the name of attribute it represents • Crow’s Foot Model • attributes are written in attribute box below entity rectangle

11. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model The Attributes of the STUDENT entity: Chen & Crow’s Foot

12. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Relationship Relationship • Associates between entities/connection between two or more entities • Logical interaction among the entities in a relational database • Operate in both directions • Chen Model • Crow’s Foot Model

13. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram Development of ER model is an Iterative Process that involved: • Step1: General narrative of organizational operations developed • Step2: Basic E-R Model graphically depicted and reviewed • Step3: Modifications made to incorporate newly discovered ER components • Repeat process: Until designers and users agree on complete E-R Diagram

14. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Model Components

15. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Entity • Corresponds to table and not to row in relational environment • Represented by rectangle containing entity’s name • Entity name, a noun, is usually written in capital letters • Examlpe: Entity STUDENTwith attributes

16. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Weak Entity • Recursive Entity • Composite Entity • Entity Supertype and Subtype

17. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Weak Entity • Existence-dependent • Entity B depends on Entity A to exist. If A does not exist then B cannot exist too • Primary key partially or totally derived from parent entity in relationship • Database designer determines whether an entity is weak based on business rules

18. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity

19. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity

20. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity employeeMANAGER employeeSPOUSE employeeNAME employeeNAME employeeNO employeeNO 1 1 EMPLOYEE EMPLOYEE 1 1 married manage Variations of Entity: • Recursive Entity • Entity set that have relationship with the same entity set • Example: EMPLOYEE entity

21. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity grade courseNAME studentNAME enroll M N courseID studentID COURSE STUDENT COURSE STUDENT STUDENT_COURSE / ENROLL Variations of Entity: • Composite Entity • Originally a relationship between 2 entities that involved in M:N relationship • Composite entity takes its primary key from both entities that it bridges • Example: enroll

22. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Entity Supertype & Subtype • Parent-Child relationship • Supertypecontains the shared attributes an entity type that include distinct subclasses that required to be presented in data model parent • Subtype contains the unique attributes an entity type that has a distinct role and also a member of supertype child

23. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Entity Supertype & Subtype • Example: Superype (EMPLOYEE) Subtype (Engineer & Full-Time)

24. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity G Gs Variations of Entity: • Entity Supertype & Subtype • Have two types of relationship:

25. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Disjoint G Gs Overlap Variations of Entity: • Entity Supertype & Subtype • Example: Disjoint & Overlap

26. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Entity Supertype & Subtype • Example: Disjoint

27. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Entity Variations of Entity: • Entity Supertype & Subtype • Example: Disjoint & Overlap

28. name course STUDENT studentID Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes email address Attributes • Represented by ovals that are connected to entity with a line • Oval contains of attribute (field) it represents • PK are underlined with straight line • FK are underlined with doted line or * • Example: Entity STUDENTwith attributes name, course, studentID, address, email

29. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes Attributes types: • Simple Attributes • Composite Attributes • Multivalued Attributes • Derived Attributes

30. studentID STUDENT Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes addressPOSTCODE addressNO addressTOWN address phoneNO Simple Attributes age name gender Attributes types: • Simple Attributes • An attribute composed of single component with an independent existence • Cannot be subdivided into smaller components • Example: gender, martial statues

31. studentID STUDENT Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes addressPOSTCODE addressNO addressTOWN address Composite Attributes phoneNO age name gender Attributes types: • Composite Attributes • An attribute composed of multiple components, each with an independent existence • Can be further subdivide to additional attributes • Example: name first, middle, last address street, city, state, zip

32. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes Attributes types: • Multivalued Attributes • attribute that holds multiple values for each occurrence of an entity type • Should not be implemented multivalued attributes in relational database • Can simplifies multivalued attributes by: • Create several attributes • Create new entity of the original multivalued attributes components • Example: phone number handset,office,home qualification diploma,degree,master

33. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes Contact hobbies Attributes types: • Multivalued Attributes

34. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes Contact hobbies Attributes types: • Multivalued Attributes

35. STUDENT STUDENT studentID Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes address handsetNO age studentID homephoneNO handsetNO gender address homephoneNO age has CONTACT gender studentID* Attributes types: • Multivalued Attributes • Can simplifies multivalued attributes by: • Create several attributes • Create new entity of the original multivalued attributes components

36. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes Attributes types: • Derived Attributes • An attributes that represents a value that is derived from the value of related attribute or set of attributes, not necessarily in the same entity type. • Need not be physically stored within database • Example: age

37. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes

38. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship • Associations /connection between entities • Logical interaction among the entities in a relational database • Operates in both directions • Naming Relationships: • Relationship name is a verb phrase • Avoid vague names • Defining Relationships: • Definition explains what action is being taken and why it is important • Give examples to clarify the action • Optional participation should be explained • Explain reasons for any explicit maximum cardinality • Explain any restrictions on participation in the relationship • Explain extent of the history that is kept in the relationship • Explain whether an entity instance involved in a relationship instance can transfer participation to another relationship instance

39. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Degree of the relationship • Connectivity of the relationship • Cardinality of the relationship • Participation

40. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Degree of the relationship • Indicates number of associated entities within the relationship • There are three types: • Unary Relationship • Association is maintained within single entity • Binary Relationship • Two entities are associated (1:1, 1:M, M:N) c. Ternary Relationship • Three entities are associated

41. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship

42. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship PK FK A PK FK Unary Relationship Type R, we identify the relation A represents the entity type involves in this relationship. Include in this relation one more time as foreign key the primary of itself. The two keys (primary key and foreign key) are the same but they represents two entities of different roles relate to this relationship.

43. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship • 1-1 Binary Relationship Type R, identify relation A and B that correspond to the entity types participating in R. The relationship itself can be mapped using one of the following approaches: • Using foreign key: This is the most popular approach. Choose one of the participating relation, say A (usually one with total participation) ; include in A as the foreign key the primary key of B. If R has attributes then put them in the relation A as well. • Merged relation: If both participations of two related entity type are total then we can merge two entity types and the relationship into a relation. • Defining relationship relation: Define a relation R to represent the relationship. All attributes of relationship is included in R. In addition, put the primary keys of two relations A , B into R. The primary keys of R is combination of primary keys of A and B. A B A B R

44. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship A B 1-N Binary Relationship Type: For each 1-N Binary Relationship Type R, identify two relations A and B correspond to two entity types participating in R. A represents the entity type at 1-side and B represents the entity type at N-side. Include the primary key of A as the foreign key in B. This foreign key represent the relationship type R.

45. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship A B S M-N Binary Relationship Type: For each M-N Binary Relationship Type R, identify two relation A, B represent two entity type participating in R. Create a new relation S to represent R. Include in S as foreign keys the primary keys of A and B and all the simple attributes of R. The combination of primary keys of A and B will make the primary key of S.

46. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Ternary Relationship Type: For each n-ary ( > 2 ) Relationships create a new relation to represent the relationship. The primary key of the new relation is the combination of the primary keys of the participating entities that hold the N (many) side. In most cases of an n-ary relationship all the participating entities hold a many side

47. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship 1 1 1 M under have RECTOR PROGRAM STUDENT UiTMBRANCH M N 1 register COURSE STUDENT Relationship is described by: • Connectivity of the relationship • Logical interaction among entities in a relational database • There are three types: • 1:1 • 1:M • M:N

48. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Cardinality of the relationship • Express the specific (minimum and maximum) number of entity occurrences associated with one occurrence of the related entity • Function of organizational policy  business rules

49. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship (1,9) (0,35) register COURSE STUDENT N M Relationship is described by: • Cardinality of the relationship • Example 1: One student can register 1 to 9 courses One course maximum can have 35 student

50. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship (0,3) (1,1) teach COURSE LECTURER M 1 Relationship is described by: • Cardinality of the relationship • Example 2: One lecturer can teaches maximum 3 courses One course can be thought by 1 lecturer only