Introduction to Databases

Understand key concepts in database systems.

Overview

Databases are used to manage large collections of data:

• Entities: physical objects, people, events
• Attributes: characteristics of entities
• Data: collect data for attributes
• Record: The set of values for one entity

Three-schema Architecture

• Internal: physical storaage structure
• Conceptual: Entities, attributes, constraints
• External: End-user views

graph:

    ExternalView1-->ConceptualSchema
    ExternalView2-->ConceptualSchema
    ConceptualSchema-->InternalSchema
    InternalSchema-->DB1
    InternalSchema-->DB2
    InternalSchema-->DB3

DBMS

A Database Management System (DBMS) supports the creation and maintenance of a database.

• A database system consists of a database and software.
• Database software consists of the DBMS and applications.

DBMS Roles

• DBA: Database administrators
• Database designers
• End users

DBMS Languages

If a DMBS does not separate the levels, DDL may be the only language used.

• SDL: Storage Definition Language (specifies the internal schema)
• DDL: Data Definition Language (may specify both conceptual and external schemas)
• VDL: View Definition Language (specifies external schema)
• DML: Data Manipulation Language

Data Models

A data model describes the structure of a database:

• Intension: The schema describes the database
• Instance: The actual data stored at a point in time
• Extension: The state of the database

Schemas change rarely while state changes constantly with every commit.

Components

Data models have three levels of component:

• Structural Component: Basic building blocks
• Integrity Component: Constraints
• Operational Component: Insert, update, delete operations

QED

© Adam Heinz

4 November 2024