Chapter 2

Database Environment

Agenda

• Three-Level ANSI-SPARC Architecture

• Database Languages

• Data Models

• Functions of DBMS

• Components of DBMS

• Data Dictionary & Information Resource Dictionary System

Three-Level ANSI-SPARC Architecture

• External– User's view

• Conceptual– Organization view– Constraints, security, & integrity

• Internal– Physical presentation– Storage, security, & encryption

Database Schemas

• Database schema (intension) & database instance (extension)

• External schemas (subschema)

• Conceptual schema

• Internal schema

Mapping

• External/conceptual mapping

• Conceptual/internal mapping

• Example

Data Independence

• Logical data independence

• Physical data independence

Database Languages

• Data Definition Language (DDL)– Structured Query Language (SQL)

• Data Manipulation Language (DML)– Procedural DML

– Non-procedural DML• Structured Query Language (SQL)

• Query-by-Example (QBE)

• Fourth-Generation Language– Form, report, graphics, & application generators

Data Models

• Definition– Integrated concept for describing data,

relationship and constraints

• Types– Object-based data models– Record-based data models– Physical data models (internal structure,

ordering, & paths)

Object-Based Data Models

• Entity-relationship– Entity, attribute, relationship– Usage

• Object-oriented– Object, class, subclass, inheritance, state

(attributes), behavior (methods or actions), encapsulation, message, polymorphism

– Usage

Record-Based Data Models

• Relational data model

• Network model

• Hierarchical Model

Relational Data Model

• Terminology– Relations

– Attributes

– Tuples

• Record relationship– One-to-many relationship

• Usage– Ad hoc reporting

• Example

Network Model

• CODASYL DBTG

• Integrated Date Store (IDS)

• Terminology– Data item & group item– Record type (owner, member)– Set type: optional, mandatory, permanent– Schema & sub-schema

Network Model

• Set– Owner & member– Singular or system– Pointer chains (single-linked, doubly linked,

member-to-owner)

• Record relationship– Many-to-many relationship

• Usage– Large volume transaction processing

Network Model

• Schema DDL– Schema description– Area description– Record Description– Set description

• Data Manipulation Language (DML)– Host language– Sub-schema DDL

Hierarchical Model• IBM

• Information Management Systems

• Terminology– Tree, general tree, & subtree

– Nodes, root node, child nodes

– Segment type

• Record relationship– One-to-many relationship

– Excellent referential integrity

– Inflexible

– No many-to-many relationship

Hierarchical Model

• Hierarchical record structure (pointer or address)– Level of tree (significant - insignificant)– Pre-order traversal or top down– Post-order traversal or bottom up– Twin pointers, forward links, backward links,

logical pointers

• Usage– Large volume transaction processing

Functions of a DBMS• Data storage, retrieval and update

• A user-accessible catalog

• Transaction support

• Concurrency control

• Recovery

• Authorization

• Integrity

• Data independence

• Data communication

• Other Utilities

Components of a DBMS

• Query processor

• Database manager

• File manager

• DML preprocessor

• DDL compiler

• Catalog manager

Components of Database Manager

• Authorization control

• Command processor

• Integrity checker

• Query optimizer

• Transaction manager

• Scheduler

• Recovery manager

• Buffer manager

SYSTEM CATALOGS

• Definition– Data dictionary– Information about database

• Types– Active– Passive– Integrated– Standalone

Information Resource Dictionary System (IRDS)

• IRDS standards by ISO• A set of rules to store and access

information in the data dictionary• Objectives: data extensibility, data integrity,

& data access control• Service interface works with: panel,

command language, export/import files, & application programs

Points to Remember

• Three-Level ANSI-SPARC Architecture

• Database Languages

• Data Models

• Functions of DBMS

• Components of DBMS

• Data Dictionary & Information Resource Dictionary System

Assignment

• Review chapter 1-2, appendix c

• Read chapter 3 & 4 (skip relational calculus 4.2)