Relationship • A relationship describes how entities interact. For example, the entity “Carpenter” may be related to the entity “table” by the relationship “builds” or “makes”. Relationships are represented by diamond shapes and are labeled using verbs 51
Cardinality • Cardinality expresses the specific number of entity occurrences associated with one occurrence of the related entity. 52
53 https://youtu.be/Tg_8UYoKoQ8 Entity Relationships Diagram A step-by-step
How to Draw ER Diagrams 1.Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly. 2.Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship. 3.Add attributes for entities. Give meaningful attribute names so they can be understood easily. 4.Add cardinality of all relationship between entities with label of 1, M or N for one-to-one, one-to-many, manyto-one or many-to-many relationship. 54
Class Activity • Create ERD for School Information System which contain: 1. Any Entities with at least two of its attributes from each of them 2. Relationship to connect all the entity with suitable labelling and cardinality 3. Example entities: Student, teacher etc. 55
Group Activity 1 • Create ERD for Library System which contain: 1. Three (3) entities with at least three (3) attributes form each of them 2. Relationship to connect all the entity with suitable labelling and cardinality MIND TEST: 56
Group Activity 2 • Create ERD for Human Resource System which contain: 1. Three (3) entities with at least three(3) attributes form each of them 2. Relationship to connect all the entity with suitable labelling and cardinality 57
Group Activity 3 • Create ERD for Airline Ticketing System which contain: 1. Three (3) entities with at least three (3) attributes form each of them 2. Relationship to connect all the entity with suitable labelling and cardinality 58
Pair Exercise 1. A company has a number of employees. Each employee may be assigned to one or more projects. A project must have at least one department assigned. Please include two (2) examples of attributes for any entities identified. 2.A university has a large number of courses in its catalogue. Each course may have one or more subjects. The subject contain several assignments. Please include two (2) examples of attributes for any entities identified. 3. A college course may have one or more scheduled classroom, or may not have a scheduled classroom. The classroom is assigned at least to one lecturer. Please include two (2) examples of attributes for any entities identified. 4.A hospital patient has a patient history. Each patient has one or more history. The history record may be assigned to at least one medicine. Please include two (2) examples of attributes for any entities identified. 5. A video store may stock more than one copy of a given movie. It is also true that the store may not have a single copy of a particular movie. A movie contain at least one chapter. Please include two (2) examples of attributes for any entities identified. 6.An employee must manage exactly one department. A department may or may not have one employee manage it. The employee must be assigned at least one task. Please include two (2) examples of attributes for any entities identified. 59
ERD QUIZ https://bit.ly/3GErVAL 60
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END OF CHAPTER 64
65 Akhlak Terbilang, Pendidikan Cemerlang