Concepts and Architecture Flashcards
(48 cards)
Client module
Runs on mobile device, PC or workstation
Handles user interaction
Server module
Handles data storage, access, search, etc.
Data abstraction
Suppression of details of organization and storage
Data model
Collection of concepts that describe the structure of the database
Representational data models
Hybrid of high level and low level models detailing how a database works
Entity
real world object or concept described in the database
Attribute
Property of interest that describes an entity
Relationship
Association of entities
Access path
search structure that makes searching efficient
Index
access path that allows direct access to the data
Database schema
description of a database specified during database design
Schema diagram
displayed database schema
Schema construct
Individual object in the schema
Database state or snapshot
Data in database at a particular moment in time
Current set of instances
Data in database at a particular moment in time
Database states
Empty state - no data
Initial state - first populated with data
Valid state - state that satisfies the structure and constraints of the schema
Current state - what data the database currently has
Meta-data
Description of schema constructs and constraints
Intension
Database schema
Extension
Database state
Schema evolution
Changes to the schema
Three Schema Architecture
Internal level - has internal schema (describes the physical storage structure of the database)
Conceptual level - conceptual schema (describes the structure of the database for a community of users)
External level - external schemes or user views (describes part of the database that a particular group is interested in)
Mappings
Transforming requests into results
Data independence
Capacity to change the schema at one level of a database without changing it anywhere else
Logical data independence
Changing conceptual schema without changing external schemes or applications
