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TAIE-08 SYSTEM ANALYSIS & DESIGN Topic 6 Structuring System Requirements: Conceptual Data Modeling Johny Hizkia Siringo Ringo BIT (Multimedia Tech.), MIMS (Soft. Dev.)
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CONCEPTUAL DATA MODEL • A conceptual data model is a representation of organizational data. • The purpose of a conceptual data model is to show as many rules about the meaning and interrelationships among data as possible, independent of any database management system or other implementation considerations. • Entity-relationship (E-R) data models are commonly used diagrams that show how data are organized in an information system.
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Entities – An entity is a person, place, object, event, or concept in the user environment about which the organization wishes to maintain data. – An entity has its own identity, which distinguishes it from every other entity. Some examples of entities follow:
Person: EMPLOYEE, STUDENT, PATIENT Place: STATE, REGION, COUNTRY, BRANCH Object: MACHINE, BUILDING, AUTOMOBILE, PRODUCT Event: SALE, REGISTRATION, RENEWAL Concept: ACCOUNT, COURSE, WORK CENTER
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ERD SYMBOLS
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Attributes – An attribute is a property or characteristic of an entity that is of interest to the organization (relationships may also have attributes, as we see in the section on relationships). – Following are some typical entity types and associated attributes: STUDENT: Student_ID, Student_Name, Address, Phone_Number, Major AUTOMOBILE: Vehicle_ID, Color, Weight, Horsepower EMPLOYEE: Employee_ID, Employee_Name, Address, Skill
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Candidate Keys and Identifiers – A candidate key is an attribute (or combination of attributes) that uniquely identifies each instance of an entity type. – An identifier is a candidate key that has been selected to be used as the unique characteristic for an entity type. or
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Relationships – A relationship is an association between the instances of one or more entity types that are of interest to the organization.
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Degree of a Relationship – Unary Relationship also called a recursive relationship, a unary relationship is a relationship between the instances of one entity type.
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING – Binary relationship is a relationship between instances of two entity types and is the most common type of relationship encountered in data modeling.
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING – Ternary relationship is a simultaneous relationship among instances of three entity types.
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INTRODUCTION TO ENTITY-RELATIONSHIP MODELING • Cardinalities in Relationships – The number of instances of entity B that can (or must) be associated with each instance of entity A.
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EXAMPLES
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EXAMPLES
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EXERCISE
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