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Entity Relationship (ER) Modeling The ER Model Developing and ER Diagram Extended ER Model Entity Integrity : Selecting Primary Key Chapter 4.

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Presentation on theme: "Entity Relationship (ER) Modeling The ER Model Developing and ER Diagram Extended ER Model Entity Integrity : Selecting Primary Key Chapter 4."— Presentation transcript:

1 Entity Relationship (ER) Modeling The ER Model Developing and ER Diagram Extended ER Model Entity Integrity : Selecting Primary Key Chapter 4

2 In this chapter, you will learn: Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 2 The main characteristics of entity relationship components How relationships between entities are defined and refined and how those relationships are incorporated into the database design process How ERD components affect database design and implementation That real-world database design often requires the reconciliation of conflicting goals

3 The Entity Relationship (ER) Model Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 3 ER model forms the basis of an ER diagram ERD represents conceptual database as viewed by end user ERDs depict databases main components: Entities Attributes Relationships

4 Entities Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 4 Refers to entity set and not to single entity occurrence Corresponds to table and not to row in relational environment In both Chen and Crows Foot models, entity is represented by rectangle containing entitys name Entity name, a noun, is usually written in capital letters

5 Attributes Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 5 Characteristics of entities In 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 In Crows Foot model, attributes are written in attribute box below entity rectangle

6 Attributes (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 6

7 Domains Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 7 Attributes have domain Domain is attributes set of possible values Attributes may share a domain a set of permitted values - ex) domain of customer--name : set of all text strings of a certain length Domains are the set of allowable data values for a Column. For example, the FiveDigitZipCode Column on the customer entity can be in the integer domain. As such, the database would not allow you to place values like 123.45 (floating point) or ABC (character) into that Column.

8 Identifiers (Primary Keys) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 8 Underlined in the ERD Key attributes are also underlined in frequently used table structure shorthand

9 Primary Key Guidelines Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 9 Attribute or combination of attributes that uniquely identifies entity instances in an entity set Main function is to uniquely identify an entity instance or row within a table Guarantee entity integrity, not to describe the entity

10 Primary Key Guidelines (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 10

11 Composite Primary Keys Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 11 Primary keys ideally composed of only single attribute Possible to use a composite key Primary key composed of more than one attribute

12 Composite Primary Keys (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 12

13 When to Use Composite Primary Keys Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 13 Useful as identifiers of composite entities, where each primary key combination is allowed only once in M:N relationship Automatically provides benefit of ensuring that there cannot be duplicate values

14 When to Use Composite Primary Keys (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 14

15 When to Use Composite Primary Keys (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 15 Useful as identifiers of weak entities, where weak entity has strong identifying relationship with parent entity Normally used to represent: A real-world object that is existent dependent on another real-world object A real-world object that is represented in data model as two separate entities in strong identifying relationship

16 Composite and Simple Attributes Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 16 Composite attribute can be subdivided Simple attribute cannot be subdivided

17 Single-Valued Attributes Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 17 Single-value attribute can have only a single value

18 Multivalued Attributes Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 18 Multivalued attributes can have many values

19 Multivalued Attributes (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 19

20 Resolving Multivalued Attribute Problems Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 20 Although conceptual model can handle M:N relationships and multivalued attributes, you should not implement them in relational DBMS Within original entity, create several new attributes, one for each of the original multivalued attributes components Can lead to major structural problems in table Create new entity composed of original multivalued attributes components

21 Resolving Multivalued Attribute Problems (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 21

22 Resolving Multivalued Attribute Problems (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 22

23 Resolving Multivalued Attribute Problems (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 23

24 Derived Attributes Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 24 Attribute whose value may be calculated (derived) from other attributes Need not be physically stored within database Can be derived by using an algorithm

25 Derived Attributes (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 25

26 Derived Attributes (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 26

27 Relationships Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 27 Association between entities Participants are entities that participate in a relationship Relationships between entities always operate in both directions Relationship can be classified as 1:M Relationship classification is difficult to establish if know only one side of the relationship

28 Connectivity and Cardinality Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 28 Connectivity Used to describe the relationship classification Cardinality Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity Established by very concise statements known as business rules

29 Connectivity and Cardinality (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 29

30 Existence Dependence Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 30 Existence dependence Exist in database only when it is associated with another related entity occurrence Existence independence Entity can exist apart from one or more related entities Sometimes refers to such an entity as strong or regular entity

31 Relationship Strength Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 31 Weak (non-identifying) relationships Exists if PK of related entity does not contain PK component of parent entity Strong (Identifying) Relationships Exists when PK of related entity contains PK component of parent entity

32 Weak (Non-Identifying) Relationships Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 32

33 Weak (Non-Identifying) Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 33

34 Strong (Identifying) Relationships Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 34

35 Weak Entities Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 35 Weak entity meets two conditions Existence-dependent Cannot exist without entity with which it has a relationship Has primary key that is partially or totally derived from parent entity in relationship Database designer usually determines whether an entity can be described as weak based on business rules

36 Weak Entities (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 36

37 Weak Entities (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 37

38 Relationship Participation Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 38 Optional participation One entity occurrence does not require corresponding entity occurrence in particular relationship Mandatory participation One entity occurrence requires corresponding entity occurrence in particular relationship

39 Relationship Participation (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 39

40 Relationship Participation (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 40

41 Relationship Participation (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 41

42 Relationship Participation (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 42

43 Relationship Degree Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 43 Indicates number of entities or participants associated with a relationship Unary relationship Association is maintained within single entity Binary relationship Two entities are associated Ternary relationship Three entities are associated

44 Relationship Degree (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 44

45 Relationship Degree (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 45

46 Recursive Relationships Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 46 Relationship can exist between occurrences of the same entity set Naturally found within unary relationship

47 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 47

48 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 48

49 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 49

50 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 50

51 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 51

52 Recursive Relationships (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 52

53 Composite Entities Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 53 Also known as bridge entities Composed of primary keys of each of the entities to be connected May also contain additional attributes that play no role in connective process

54 Composite Entities (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 54

55 Composite Entities (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 55

56 Composite Entities (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 56

57 Developing an ER Diagram Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 57 Database design is iterative rather than linear or sequential process Iterative process Based on repetition of processes and procedures

58 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 58 Building an ERD usually involves the following activities: Create detailed narrative of organizations description of operations Identify business rules based on description of operations Identify main entities and relationships from business rules Develop initial ERD Identify attributes and primary keys that adequately describe entities Revise and review ERD

59 Developinag an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 59 Tiny College Tiny College is divided into several schools Each school is composed of several departments Each department may offer courses Each department may have many professors assigned to it Each professor may teach up to four classes; each class is section of course Student may enroll in several classes, but (s)he takes each class only once during any given enrollment period

60 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 60 Tiny College (continued) Each department has several students Each student has only a single major and is associated with a single department Each student has an advisor in his or her department Each advisor counsels several students The relationship between class is taught in a room and the room in the building

61 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 61

62 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 62

63 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 63

64 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 64

65 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 65

66 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 66

67 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 67

68 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 68

69 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 69

70 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 70

71 Developing an ER Diagram (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 71

72 Data Modeling Checklist Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 72

73 Summary Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 73 Entity relationship (ER) model Uses ERD to represent conceptual database as viewed by end user ERMs main components: Entities Relationships Attributes Includes connectivity and cardinality notations

74 Summary (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 74 Connectivities and cardinalities are based on business rules In ERM, M:N relationship is valid at conceptual level ERDs may be based on many different ERMs Database designers are often forced to make design compromises

75 Summary Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 75 Extended entity relationship (EER) model adds semantics to ER model via entity supertypes, subtypes, and clusters Specialization hierarchy depicts arrangement and relationships between entity supertypes and entity subtypes Inheritance allows an entity subtype to inherit attributes and relationships of supertype

76 Summary (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 76 Composite keys are useful to represent M:N relationships and weak (strong-identifying) entities

77 Summary (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 77 Surrogate primary keys are useful when there is no natural key that makes a suitable primary key In a 1:1 relationship, place the PK of mandatory entity as foreign key in optional entity Time-variant data refers to data whose values change over time and whose requirements mandate that you keep a history of data changes

78 Summary (continued) Chapter 3 | Entity Relationship (ER) Modeling Prepared by : Maizatul Akma bt Napiah 78 Data modeling checklist provides way for designer to check that the ERD meets set of minimum requirements


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