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CPSC 471 Study Guide - Midterm Guide: Foreign Key, Data Integrity, Unique Key

Computer Science
Course Code
CPSC 471
Nelson Wong
Study Guide

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CPSC 471
Midterm Study

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Data Model: set of concepts -with constraints- to describe the structure of database
o Categories:
Conceptual/Entity based (high level and semantic)
Way many users perceive data
Physical (low level, internal)
Details of how data is stored in the computer
Representational (implementation)
User views with some computer storage details
Schemas and States
o Database Schema: Description of the structure and constraints of the database
Schema Diagram: Diagrammatic display
Schema Construct: Components of the schema
o Database State: Contents of the database at a moment
Initial DB State: When it’s loaded
Valid State: Satisfies the structure and constraints
o Distinction
DB Schema changes very infrequently, but the DB State changes every time DB is updated
Schema: Intension; State: Extension
Three-Schema Architecture
o External S:
Describes various user views
Uses conceptual level model
o Conceptual
Structure and constraints
Conceptual or implementation model
o Internal Schema
Physical storage structure and access paths
Physical data model
Data Independence
o Logical: Can change the conceptual schema without changing the external one and its applications
o Physical: Can change the internal schema without changing the conceptual schema
o DBMS Languages
Data Definition Language
Specifies the conceptual schema, and define internal and external schemas
Data Manipulation Language
Specifies database retrievals and updates and its commands (data sublanguage) can be
embedded in a general-purpose programming language
High-level/Declarative Language
Specifies what to do (what data to retrieve) and not how to do
Low Level/Procedural Language
Specifies how to do and how what to do
o DBMS Interfaces
General Interfaces (can be combined)
Menu-based (browsing on web), form based (naïve users), graphic-based (point, drag-drop),
natural-language (requests written in English)
Other interfaces
Speech as I/O, web browser, parametric using function keys, DBA (create acc, grant auth.)
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