ER-L1L2

ER-L1L2 - Conceptual Design using the ER model Module 2...

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Conceptual Design using the ER model Module 2   Lectures 1 and 2
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A simplified database design process UoD Requirements Collection and Analysis Database Requirements Functional Requirements
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A simplified database design process Database Requirements Functional Requirements Conceptual Design Functional Analysis Conceptual Schema High-level Transaction Specs DBMS INDEPENDENT
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A simplified database design process Physical Design Application program Design Conceptual Schema High-level Transaction Specs DBMS DEPENDENT Transaction Implementation Internal Schema Application software
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Conceptual Schema Outcome of the high-level conceptual design Concise description of data requirements of the users Includes description of entity types, relationships and constraints No implementation details Ease of understanding. Used to communicate with non-technical users
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Example COMPANY Database Departments: Name, Dept_id, Manager, … Projects: Name, Proj_id, Location (managed by departments) Employee: Name, PAN, Address, Salary, Gender, DOB,… Dependents: Name, Address, Gender, DOB, Relationship with employee
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Entities and Attributes Department Dept Name Dept_Id Manager An entity represents an object of the real world that has  an independent existence.  An entity has attributes – properties that describe it.  
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Attribute types Simple vs Composite A composite attribute is made of one or more simple or composite attributes. Ex. Name is made of First Name, Middle Name and Last Name Single-valued vs Multi-valued A single valued attribute is described by one value (Example, age of a person). A multi-valued attribute is described by many values (Example, the colour attribute of a multi-coloured bird)
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Attribute types Stored vs Derived An attribute whose value can be inferred from the value of other attributes is called a derived attribute (Example, age can be derived from date of birth and current date). If this is not the case, then it is a stored attribute. Null Values Attributes that do not have any applicable values are said to have null values. Different from 0, unknown and missing values
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Entity Types and Entity Sets An Entity Type defines a collection of different entities having the same type. For example, “Department” defined earlier is an entity type defining several department having the same attribute structure Any specific collection of entities of a particular type is called an Entity Set. An Entity Type describes the schema or intension for an Entity Set.
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Representations Entity Types Attributes Multi-valued Attributes Derived Attributes
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Key Attributes Department Dept Name Dept_Id Manager The Dept_id attribute is unique for each department   belonging to this entity set.  The Dept_id can hence  uniquely identify  departments.
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Key Attributes An attribute or a set of attributes that uniquely identify entities in an entity set are called
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ER-L1L2 - Conceptual Design using the ER model Module 2...

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