Intro to Database Systems Flashcards
Data
known facts with implicit meaning
Database
a highly organized, interrelated, and structured set of data
DBMS
Database Management System: Defines a database in terms of its data types, structures, and constraints
Example: University DB
Data: students, instructors, and courses
Applications: add course, register students, assign grades, compute gpa
Example: University DB relationships
STUDENTs take COURSEs
INSTRUCTORs teach SECTIONs
STUDENTs major in DEPARTMENTs
Main Characteristics of DBs
Self-describing, program-data independence, data abstraction, multiple view support, multi-user processing
C1: Self-Describing
DBMS contains description of db
C2: Program-data independence
insulation bw programs and data, data structures can change without modifying the whole DBMS
C3: Data abstraction
data model can be used to display conceptual view of db
C4: Multiple view support
Users can have different views of the db
C5: Multi-user processing
Allows for concurrent retreival and updates from many users
Database users
end-users, database designers, database administrators
End-users
mainly views data, can update content
Database designers
define the content, structure, constraints, and funtions of db
Database administrators
authorizes access, monitors and controlls its use
Data model
set of concepts to describe the structure of a db
Conceptual model
high-level; provides concepts of how users perceive data
Logical model
detailed description of data entities and relationships, no physical details
Physical model
low-level; describes how data is stored
Database schema
description of db
Database state
the actual data stored in a db at a particular time (aka instance)
Three-schema architecture
Internal: physical storage
Conceptual: structure and constraints of db
External: different user views of db
Logical data independence
ability to change conceptual schema without changing external schema
Physical data independence
ability to change internal schema without changing conceptual schema
