Punjab College Of Technical EducationPresentation On:- College Website
E-R Model E-R Model: Entities. Attributes. Relationship. Steps to form E-R Model: Identify Entities. Find Relationship. Draw rough E-R. Fill the cardinality. Define Primary key. Draw key based ERD. Identity Attributes. Map Attributes. Draw full attribute of ERD. Check Result.
• Store Information in Systematic Manner• Reduce the Problem of End-user• Easy to Store an Retrieval• Track the Information
Users• Different users can access data• Depending on their degree of expertise users are classified in the following groups – Naïve Users (ATM user) – Online Users – Application Programmers – Sophisticated Users – DBA
Entity Relationship Model• Entity – It is anything real or abstract about which we want to store the data .• Relationship – It specifies the association that exists between one or more entities.• Attribute – It is the characteristic which is common to all or most instances of particular entity.
Dependencies What is Dependencies? Types of Dependencies Partial key Dependencies. Primary key Dependencies. Transitive key Dependencies. Functional key Dependencies.
Specialization StudentGrad Student Post Grad Student
Normalization• It is a process during which redundant relation schemas are decomposed by breaking up their attributes in to smaller relation schemas that possess desirable properties.1. First N/F2. Second N/F3. Third N/F4. BNC N/F
Normalization Form BC N/F Third N/F Second N/F Eliminate First N/F Eliminate Functional Transitive key dependency Removing dependency Partial keyEliminate dependencyRepeatingGroups
Attributes• Characteristics of entities• Domain is set of possible values• Primary keys underlined
Relationships • Association between entities • Connected entities are called participants • Operate in both directions • Connectivity describes relationship classification – 1:1, 1:M, M:N • Cardinality – Expresses number of entity occurrences associated with one occurrence of related entity12
Comparison of E-R Modeling Symbols Figure 3.3613
Keys• Candidate Key – A minimal set of attributes that uniquely identifies a tuple• Primary Key – The candidate key chosen as the identifying key of the relation• Alternate Key – Candidate keys which are not primary keys
• Foreign Key – An attribute (or set of attributes) in table R1 which also occurs as the primary key of relation R2. – R2 is called the referenced relation. – Foreign keys are also called connection keys or reference attributes.