8/6/2023 Badakhshan University Faculty of Computer Science 1 Islamic Republic of Afghanistan Ministry of Higher Education Badakhshan University Computer Science Faculty Database Fundamentals 8/6/2023 Badakhshan University Faculty of Computer Science 2 Lecture #6 Entity Relationship (E-R) Model) (Continue) 8/6/2023 Badakhshan University Faculty of Computer Science 3 Elements of ER Model……. Entity relationship ( E-R ) Model involve different types of elements such us: 1 . Entity 2. Attribute 3. Relationship 8/6/2023 Badakhshan University Faculty of Computer Science 4 3. Relationship : A relationship is an association representing an interaction among the instance of one or more entity types that is interest to the organization The relationship may be between different entities or between an entity itself. A relationship is established on the basis of interaction among these entities. For example : a relationship exist between employ and department because the employ works on department 8/6/2023 Badakhshan University Faculty of Computer Science 5 Attribute on Relationship Some times there are some attributes that is represented in the time of relationship. These attributes have its own meaning in ER diagram. That attribute which are represented in the time of relationship are not associated or related to another entity, because these attributes are the properties of relationship For example : we have two entity TEACHER and COURSE 8/6/2023 Badakhshan University Faculty of Computer Science 6 Example Attributes of Relationship COMPLETE 8/6/2023 Badakhshan University Faculty of Computer Science 7 Associative Entity : Associative entity is a type of entity that associates the instance of one or more entity types Associative entity contain the attributes that are related to the relationship, these attributes are not related to another entity which are presented in the relationship Associative entities are represented as rectangle with rounded corners. In ER diagram the associative entity has independent meaning to end user 8/6/2023 Badakhshan University Faculty of Computer Science 8 Degree of Relationship : Each relationship consist of many entities. The degree of relationship is the number of entity types that participate in the relationship is called degree of relationship. There are three most common relationship degree in E-R model 1. Unary Relationship 2. Binary Relationship 3.Ternary Relationship 8/6/2023 Badakhshan University Faculty of Computer Science 9 1.Unary Relationship : Unary Relationship is a type of relationship that is established between the instance of a single entity type or it is established between the instance of same entity type. PERSON manage Teach Lives with 8/6/2023 Badakhshan University Faculty of Computer Science 10 2. Binary Relationship : Binary Relationship is a type of relationship that is established between the instance of two entity type It is the most common type of relationship in data modeling There are different types of binary relationship 1. One –to- one Relationship 2. One-to-many Relationship 3. Many-to-many Relationship 8/6/2023 Badakhshan University Faculty of Computer Science 11 1.One-to-one Relationship : This is a type of relationship is used when, for each instance in first entity type there is only one instance in the second entity type. And for each instance in the second entity type, there is only one instance in the first entity type . 1 MANAGER 1 manage BRANCH The above relationship means that one manager manage one branch. Similarly, one branch is manage by one manager. 8/6/2023 Badakhshan University Faculty of Computer Science 12 Example of One to One Relationship 8/6/2023 Badakhshan University Faculty of Computer Science 13 Example of One-to-One Relationship : 1 Has COUNTRY Has 1 PRESIDENT The above relationship means that one country has one president. Similarly, one president of only one country 1 CHAIRMAN 1 Run UNIVERSITY The above relationship means that one chairman run only one university. Similarly, one university is run by one chairman 8/6/2023 Badakhshan University Faculty of Computer Science 14 Example of One-to-One Relationship : MAYOR 1 MANAGER 1 Has PROVINCE 1 1 8/6/2023 GOVERNER 1 1 CITY BRANCH Manage Has MAYOR Badakhshan University Faculty of Computer Science 15 2. One-to-Many Relationship : This is a type of relationship is used when, for each instance in first entity type there can be many instance in the second entity type. And for each instance in the second entity type there is only one instance in the first entity type. 1 M Has The above relationship means that one province can have many district, but one district is only belong to one province. 8/6/2023 Badakhshan University Faculty of Computer Science 16 One-to-Many Example 8/6/2023 Badakhshan University Faculty of Computer Science 17 Many-to-One Example 8/6/2023 Badakhshan University Faculty of Computer Science 18 Example of One-to-Many Relationship 1 M Has the above relation means that one faculty can have many departments, but one department is only belong to one faculty. 1 M Work the above relationship means that in one department can work many employ, but one employ can only work on one department 8/6/2023 Badakhshan University Faculty of Computer Science 19 Example of One-to-Many Relationship COUNTRY Has PROVINCE Faculty Has DEPARTMENT HASBAND Has WIFE 8/6/2023 Badakhshan University Faculty of Computer Science 20 3. Many-to-Many Relationship : Many-to-Many Relationship is a type of relationship used when, for each instance in first entity type, there can be many instance in the second entity type And for each instance in second entity type, there can be many instance in the first entity type Study The above relationship means, that one student may study more course, and one course may be studied by more students 8/6/2023 Badakhshan University Faculty of Computer Science 21 Many-to-Many Example 8/6/2023 Badakhshan University Faculty of Computer Science 22 2. Many-to-Many Relationship : Has The above relationship means that one employ learn many skills and one skill can be learned by many employees. Read The above relationship means that one reader may read many books and one book may be read by one reader 8/6/2023 Badakhshan University Faculty of Computer Science 23 Any Questions & Suggestions Email: mqm.dacaar@gmail.com Phone: +0789152242 8/6/2023 Badakhshan University Faculty of Computer Science 24
