Chapter 13-1

Chapter 13-2

Chapter 13Data Modeling

Introduction

An Overview of Databases

Steps in Creating a Database Using Rea

Creating Database Tables and Records

Chapter 13-3

Introduction

Modern AISs use computers

to systematically record data, in convenient and useful formats

to provide easy access to required information.

Chapter 13-4

An Overview of Databases

A database is a collection of data that is stored in related files.

Databases are important because they:contain valuable information,

are very large in volume,

store data in all its complexity

have to maintain privacy

contain irreplaceable data

have to be complete, comprehensive, and accurate

are priceless to Internet users

Chapter 13-5

Question

Which of these does not characterize a typical database?

a. large number of records

b. irreplaceable data

c. high need for accuracy

d. simple systems

An Overview of Databases

Chapter 13-6

To be useful, the data in an organization’s databases must be stored and organized efficiently.

The three important concepts are Data hierarchy Record structures Record keys

Storing Data in Databases

Chapter 13-7

Data Hierarchy

Storing accounting data in computer files involves organizing the data into a data hierarchy.

The lowest level of information in a file is a binary digit or bit.

Eight bits create a byte that represents a character.

A data field combines several characters or bytes.

A record combines related data fields.

A set of records forms a file.

A database is a collection of files thatcontain all the information for an application.

Chapter 13-8

Question

Which of these is not part of the ‘‘data hierarchy’’ (within the context of databases)?

a. Record

b. bit

c. character

d. data type

Data Hierarchy

Chapter 13-9

Record Structures and Record Keys

The specific data fields in each record of a computer file are part of the record structure.

Record Keys are identifiers for records:

Primary keys are unique to each record

Secondary keys are non-unique identifiers for records and used for searching files for specific information

Foreign keys enable database records toreference one or more records in other files

Chapter 13-10

Additional Database Concerns

Administration

Documentation

Data integrity

Processing Accuracy and Completeness

Concurrency

Backup and Security

Chapter 13-11

Administration and Documentation

A database administrator supervises the design, development, and installation of alarge database system, and

is responsible for its maintenance, security and revision

Documentation involves descriptions of

database structures,

contents,

security features,

E-R diagrams, and

password policies

A data dictionary is a data file about data.

Chapter 13-12

Data integrity ProcessingAccuracy and Completeness

Data integrity controls are

designed by the database developers and

are customized for the application at hand.

To achieve transaction controls database systems

maintain an auditable log of transactions

Chapter 13-13

can recover by verifying that a problem has happened, reversing whatever entries were made, and starting anew. In

have the ability to audit any particular transaction to ensure processing accuracy and completeness.

Data integrity ProcessingAccuracy and Completeness

Chapter 13-14

ConcurrencyBackup and Security

Concurrency controls are necessary toprevent multiple-user access to the same file

execute transactions sequentially

Information in many accounting databases

must be protected is stored by backup procedures for retrieval is protected from unauthorized access by use of

passwords encryption techniques

Chapter 13-15

Question

Within the context of databases, the term ‘‘concurrency’’refers to the possibility that

a. a customer of one store might also be a customer of another store.

b. two database users might want to access the samerecord at the same time.

c. a credit entry for a customer requires a debitentry for a matching account.

d. none of these

ConcurrencyBackup and Security

Chapter 13-16

Steps in CreatingDatabases with REA

An events-based accounting system (EBA) records activities that actually happen.

The REA is a tool for designing databases.

An AIS captures data about an organization’s resources, events and agents (REA). Resources are an organization’s assets. Events are identifiable activities associated with

a business processes. Agents are the people associated with business activities.

Chapter 13-17

Question

In the REA model, the ‘‘A’’ stands for:

a. agents

b. additions

c. accounts

d. associations

Steps in CreatingDatabases with REA

Chapter 13-18

The REA model requires the following steps:identify business and economic events,

identify entities,

identify relationships among entities,

create Entity-Relationship diagrams,

identify the attributes of data entities, and

create database tables and records tovalidate the database.

Steps in CreatingDatabases with REA

Chapter 13-19

Identify Events and Entities

Business processes involve two types of events:economic events that impact an organization’s financial statements

business events, that impact an organization in a value-added way

Database entities includebusiness and economic eventsinformation about the agents were involved in them

the resources that events use or generate.

Chapter 13-20

Identify RelationshipsAmong Entities

An entity-relationship (ER) diagram graphically depicts a database’s contents.

An entity relationship may be direct relationship or

indirect relationship

ER diagrams depict entities being modeled and

the relationships (cardinalities) among them.

Chapter 13-21

The E-R model uses diamond symbols to represent relationships.

include symbols (“1” or “*”) that provide informationon cardinality.

The cardinality of a relationship describes the number of occurrences of one entity that may be associated with a single occurrence of the other entity.

Entity-Relationship Modeling

Chapter 13-22

Cardinality Relationships

Cardinality can be One-to-one (1:1)

One-to-many (1:*),

many-to-one (*:1), or

Many-to-many (*:*)

Cardinalities provide useful information about the nature of the company being modeled and

the business policies that it follows.

Chapter 13-23

Question

Which of these is not a cardinality between two database entities?

a. one-to-one

b. none-to-none

c. one-to-many

d. many-to-many

Cardinality Relationships

Chapter 13-24

Organizing Database Records

The structure of a databaseis a particular method used to organize records

aims to develop this efficiently so that data can be accessed quickly and easily.

The three types of structures are: hierarchical,

network and

relational.

Chapter 13-25

Hierarchical Structures

Accounting data are often organized in a hierarchy.

A hierarchical structure has successive levelsof data in an inverted treelike pattern, known as tree structures.

higher level records are parent records and lower level records are child records two records on same level are sibling records.

Chapter 13-26

Network Structures

Databases can use a network structure to link

related records together and

capture many-to-many relationships.

The linking is accomplished with pointer fields.

The pointers maintain the data relationships.

Chapter 13-27

Relational Structures

Relational databases are more flexible.

Users can define relationships

when the database is created or

at later points in time.

Chapter 13-28

Creating DatabaseTables and Records

An Introduction to Microsoft Access

Creating Database Tables

Creating Records

Creating Database Relationships

Guidelines for Creating Database Tablesand Records

Chapter 13-29

Microsoft Access andDatabase Tables

Microsoft Accessis a popular relational database used by many businesses and individualsused for small database applications

Creating database tables requires three items: Field Name, names assigned to the data fields

Data Type, to be specified for each data field

Description optional field that defines record structures

Chapter 13-30

Creating Records and Database Relationships

Creating recordsindividual records for the data fields

Database relationshipslink tables together enable users to create multitable reports

To create database relationshipslaunch the relationships window, select tables, andlink the tables.

Chapter 13-31

Guidelines for CreatingDatabase Tables and

RecordsSome guidelines for creating database tablesand records:

Design first; create tables and records last.

Name tables systematically and use conventional tbl prefixes.

Use mnemonic names for data fields.

Assign correct data types to data fields.

Data fields that link tables must be the same data type.

Limit the size of text data fields to reasonable lengths.

Use input masks.

Chapter 13-32

Copyright

Copyright 2005 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without theexpress written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchasermay make backup copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.

Chapter 13-33

Chapter 13