Week 2 Flashcards
What is the Three-level Architecture?
View 1 View 2 View 3 1*
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Conceptual Level 2*
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Internal Schema 3*
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Database
1* The way users percieve the data
2* Provide both mapping and desired independance
3* The way DMBS and the operating system perceive the data
What is the External level of Three-Level Architecture?
View Level
Describes part of the data that is relevant to users
What is the Conceptual Level in Three-Level Architecture?
Describes WHAT data are stored in the database and relationships among the data
What is the Internal Level in Three-Point Architecture?
Describes HOW data actually stored and how files and indexes are organised and used
What is Data Abstraction?
Hide storage details and present users with conceptual view of database
What is Data Independance?
Capacity that upper levels are unaffacted by changes to lower level
What is Database Schema?
Description of the structure of Database
What is Database State?
Content of DB at moment in time
What is Initial Database State?
Content of the Database when it is created
What is a Data Model?
Set of concepts to describe:
- Data and relationships among data
- Data constraints
What is a Cone ceptual Data Model?
Indentifies high level data structure
Independant of DBMS, application programs and physical considerations
What are the 3 types of Logical Data Models?
- Hierarchical
- Network
- Relationall
What is a HierarchicalData Model?
Data is organised in tree-like structure
a node only has one parent
What is a Network Data Model?
Data organised into graph
One node can have more than 1 parent at a time
What is a Relational Data Model?
Way of structuring data in database that emphasizes relationships between data entities
