dbms conceptual modeling, Lecture notes of Database Management Systems (DBMS)

Download dbms conceptual modeling and more Lecture notes Database Management Systems (DBMS) in PDF only on Docsity! Conceptual Modelling using ER model- Day 1 CS105:DATABASE MANAGEMENT SYSTEMS ISURA NIRMAL |ISURA.N@NSBM.LK| SCHOOL OF COMPUTING Entity Relationship Model Entity Relationship(ER) Model is a conceptual data model which can be used in designing a database. The three main constructs of the ER model are, ◦ Entities ◦ Attributes ◦ Relationships ER Model is an Illustration. So we need a Modelling Notation ◦ Standard Symbols to use ◦ Chen Notation Types of Entities Strong (Regular) Entity ◦ An entity that exists independently of other entity types Weak Entity ◦ An entity types whose existence depends on some other entity ◦ This is depended on the scenario (interaction with other entities) ◦ I.e :- A call cannot exist without phone (phone number) Represented by using a rectangle What is “Attribute” Entities are represented by means of their properties called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes. Represented using an Eclipse Every ellipse represents one attribute and is directly connected to its entity Types of Attributes Simple attribute/Single-value attribute An attribute that cannot be broken down into smaller components Composite attribute An attribute that can be broken down into component parts Derived attribute An attribute whose values can be calculated from related attribute values Some Examples oe Some = ‘s Examples & Now your turn (H/W) We want to represent information about products in a database. Each product has a description, a price and a supplier. Suppliers have addresses, phone numbers, and names. Each address is made up of a street address, a city, and a postcode.