an introduction to database management systems r. nakatsu

An Introduction to Database Management Systems

R. Nakatsu

Why do we need a database?

Data is easier to manage Too much data in individual files Too many separate files

Need multiple views of data Improved data sharing (concurrent updating) Improved data security Databases can better enforce data quality Leads to better data integration

File-Processing Systems

Problems with File-Processing Systems

Data are separated and isolated Data are often duplicated Incompatible data files Program-Data Dependence

Databases are Centralized

What is a database?

A database is an integrated collection of logically related data elements. A database consolidates records previously stored in separate files.

A database can be viewed as the topmost element of a data hierarchy: database (a set of related files) file (a collection of related records) record (a group of logically related fields) field (an attribute) character (single alphabet, number, or other symbol)

Database Systems, 9th Edition

Table Row Column

File Record Field

Relation Tuple** Attribute

Related Terminology: Three ways to refer to the same thing

**Rarely used terminology

Database Components

Page 26© 2000 Prentice Hall

Types of Data

1. User data

2. Metadata

3. Indexes

4. Application Metadata

1. User Data

A table of data is called a relation Columns are fields or attributes Rows are specific instances Relations must be structured properly

2. Metadata or Data Dictionary“a description of the structure of the database”

System tables store metadata, including: table names field names primary key fields data types field size data constraints (e.g., input masks, and validation rules) relationships between tables

3. Indexes

Improve performance Improve accessibility (Overhead data)

Physical vs. Logical Storage

Physical Storage is how the computer actually stores the data

Logical Storage is how the human end-user views or perceives the data

Indexes create a logical view on your data.

4. Application Metadata

Stores the structure and format of: forms reports queries other application components

Hierarchy of Data Elements

Database Management System (DBMS)

A DBMS (database management system) is a set of computer programs that is used to create, maintain, and provide controlled access to user databases

DBMS: Main Functions Data definition

Define what data is stored, the type of data, how the data is related.

You can also specify how the data can be formatted and validated

Data manipulation You can select which data you want, filter it, sort it, join

it with other data, summarize it. Application Development

Graphical tools to develop menus, forms, and reports Data control

Allows you to specify security, transaction management, backup and recovery

Databases for Competitive Advantage: WalmartContinuous Replenishment System:

Point of sale terminals record the bar code whenever a customer purchases a product.

A database stores inventory data

Suppliers can access Walmart’s sales and inventory data online using the Web.

Strategic Information Systems

Computer systems that help the organization gain a competitive advantage. Systems can be created to:

Explore, identify, and occupy new market niches.

Understand the customer value chain better.

Learn faster and more deeply than competitors.

RECAP

Why do we need a database? File processing systems vs. databases What is a database? The DBMS The four types of data Databases for Competitive Advantage