Database
Management
Systems
Lecture - 3
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Database Architecture, Data Independence - Database Management - Lecture Slides, Slides of Introduction to Database Management Systems
Database Architecture, Data Independence, DBMS functionalities, Three levels, Objective, Physical representation, Refers to permanent structure are the main points of this lecture.
Typology: Slides
2011/2012
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Database
Management
Systems
Lecture - 3
Lecture Overview
Database Architecture
Data Independence
Three Level
Architecture
A basis for understanding DBMS functionalities
Three levels at which data can be described
Objective
Separate users view from the physical representation
Why? Different views of same data Consolidated representation Both ways easy change
The Architecture
Depicted by three schemas or three models
Refers to permanent structure or intention of database
Level 1 External View
The way users think about data
External View
Users may have different views of the same data e.g. date, time etc.
External View
Virtual/calculated data: that is not actually stored in the database but is created when needed e.g. age, statistical data etc. Docsity.com
External View
User’s external view is created after considering data access, reports, and the transactions needs.
External View
External schema evolves as user needs are modified over time
Level 2 Logical or Conceptual View
A complete description of the information content of the database
Conceptual Schema
The entire information structure of the database, as seen by the DBA The community view of data
Conceptual Schema
Contains record types representing entities, data item types with their attributes, relationships and constraints on data.
Conceptual Schema
Contains Semantic information about the data meaning, security and integrity information