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Understanding Entity-Relationship Modeling (E-R) in Database Management Systems

Chapter 4 of the course on Database Management Systems introduces Entity-Relationship (E-R) Modeling, providing essential insights into how data structures are represented in relational database design. This chapter discusses the importance of E-R Diagrams (ERDs) in visualizing complex data relationships and assists designers in developing effective database solutions. Key concepts like entities, attributes, and relationships are explored, along with methodologies for creating and refining E-R models. Understanding these foundational concepts is critical for effective database design and communication among stakeholders.

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Understanding Entity-Relationship Modeling (E-R) in Database Management Systems

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  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 • 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 the relational database modeling • gives data structures representation of: • what information have 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 database’s main components: • Entities • Attributes • Relationships

  9. Chapter 4: Entity Relationship (E-R) Modeling4.1 The Entity Relationship (E-R) Model: Entity Entity • 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 • 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 • 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 yield 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. 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

  34. studentID STUDENT Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Attributes address phoneNO name age Derived Attributes gender 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, cgpa

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

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

  37. 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

  38. 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 c. Ternary Relationship • Three entities are associated

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

  40. 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

  41. 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 number of entity occurrences associated with one occurrence of the related entity • Function of organizational policy  business rules

  42. 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

  43. 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

  44. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Cardinality of the relationship • Example 3:

  45. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Cardinality of the relationship • Relationship Strength  Existence Dependence • Existencedependence • Entity exists in database only when it is associated with another related entity occurrence • Existenceindependence • Entity can exist apart from one or more related entities • Sometimes such an entity is referred to as a strong or regular entity

  46. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Relationship is described by: • Cardinality of the relationship • From Existence Dependence, exist two relationship strength: • Weak Relationship • Entity not existence-independent on other entity • PK of related entity doesn’t contain PK component of parent entity • Non-Identifying Relationship • Strong Relationship • Existence dependence • PK of related entity contains PK component of parent entity • Identifying Relationship

  47. Chapter 4: Entity Relationship (E-R) Modeling4.2 Developing An E-R Diagram: Chen Model: Relationship Database Systems, 9h Edition

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

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