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©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

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Accounting Information Systems9th Edition

Marshall B. Romney

Paul John Steinbart

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

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Relational Databases

Chapter 4

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Learning Objectives

1. Explain the difference between database and file-based legacy systems.

2. Describe what a relational database is and how it organizes data.

3. Explain the difference between logical and physical views of a database.

4. Create a set of well-structured tables to properly store data in a relational database.

©2003 Prentice Hall Business Publishing, Accounting Information Systems, 9/e, Romney/Steinbart

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Introduction

Ashton Fleming, the accountant for S&S, believes that the best way to provide Susan Gonzalez and Scott Parry with easy access to the information they need to run their business is to build S&S’s new AIS as a database system.

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Introduction Ashton decides to prepare a brief

report for them addressing the following questions:

What is a database system? What is a relational database system? How do you design a relational

database?

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Introduction This chapter explains what a

database is and how it differs from a file-oriented system.

It also describes the structure of a relational database system.

The chapter concludes by discussing the basic steps involved in designing a database.

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Learning Objective 1

Explain the difference between database and file-based legacy systems.

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Types of Files

Two basic types of files are used to store data.

1 The master file, which is conceptually similar to a ledger in a manual system.

2 The transaction file, which is conceptually similar to a journal in a manual system.

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File Approach

For many years, companies created new files and programs each time an information need arose.

This proliferation of master files created problems:

1 Often the same data was stored in two or more separate files.

2 The specific data values stored in the different files were not always consistent.

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File-Oriented Approach

Shipping Program

SalesProgram

File 1Fact A Fact B Fact C

File 2Fact B Fact D Fact E

BillingProgram

File 3Fact A Fact G Fact E

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Databases The database approach views data as an

organizational resource that should be used by, and managed for, the entire organization, not just the originating department or function.

Its focus is data integration and data sharing. Integration is achieved by combining master

files into larger pools of data that can be accessed by many application programs.

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Databases

Database management system (DBMS) is the program that manages and controls access to the database.

Database system is the combination of the database, the DBMS, and the application program that uses the database.

Database administrator (DBA) is the person responsible for the database.

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Database Approach

Billing Program

ShippingProgram

Databasemanagement

system

Sales Program

Fact A

Fact B

Fact C

Fact D

Fact E

Database

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Learning Objective 2

Describe what a relational database is and how it organizes data.

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Relational Databases

A data model is an abstract representation of the contents of a database.

The relational data model represents everything in the database as being stored in the form of tables.

Technically, these tables are called relations.

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Relational Databases

Each row in a relation, called a tuple, contains data about a specific occurrence of the type of entity represented by that table.

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Learning Objective 3

Explain the difference between logical and physical views of a database.

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Logical and PhysicalViews of Data

A major advantage of database systems over file-oriented systems is that the database systems separate the logical and physical view of data.

What is the logical view?It is how the user or programmer

conceptually organizes and understands the data.

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Logical and PhysicalViews of Data

What is the physical view?It refers to how and where the data

are physically arranged and stored on disk, tape, CD-ROM, or other media.

The DBMS controls the database so that users can access, query, or update it without reference to how or where the data are physically stored.

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Logical and PhysicalViews of Data

Logical View User A Logical View User B

Past Due AccountsName Balance DaysJackson 2145 48Houston 1595 65

October Sales by Region

OperatingsystemDBMS

Database

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Logical and PhysicalViews of Data

Program-data independence is the separation of the logical and physical views of data.

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Schemas

A schema describes the logical structure of a database.

There are three levels of schemas:1 Conceptual-level schema2 External-level schema3 Internal-level schema

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Schemas

The conceptual-level schema is an organization-wide view of the entire database.

The external-level schema consists of a set of individual user views of portions of the database, also referred to as a subschema.

The internal-level schema provides a low-level view of the database.

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Schemas

r rJackson 210Houston 100

xxxxxxxxxxxxxx

Mapping external level views to conceptual level schema

Subschema A Subschema B Subschema C

Inventory Sales Customer

Cash receipt

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Schemas

Mapping conceptual level facts to internal level descriptions

Inventory Sales Customer

Cash receipt

Inventory Record Item number – integer (5), non-null, index = itemx Description – character (15)

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The Data Dictionary

The data dictionary contains information about the structure of the database.

For each data element stored in the database, such as the customer number, there is a corresponding record in the data dictionary describing it.

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The Data Dictionary

The data dictionary is often one of the first applications of a newly implemented database system.

What are some inputs to the data dictionary?– records of any new or deleted data

elements– changes in names, descriptions, or

uses of existing data elements

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The Data Dictionary What are some outputs of the data

dictionary?– reports useful to programmers,

database designers, and users of the information system

What are some sample reports?– lists of programs in which a data item is

used– lists of all synonyms for the data

elements in a particular file

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DBMS Languages

Every DBMS must provide a means of performing the three basic functions:1 Creating the database2 Changing the database3 Querying the database

The sets of commands used to perform these functions are referred to as the data definition, data manipulation, and data query languages.

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DDL Language

The data definition language (DDL) is used to...– build the data dictionary.– initialize or create the database.– describe the logical views for each

individual user or programmer.– specify any limitations or constraints

on security imposed on database record or fields.

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DML Language

The data manipulation language (DML) is used for data maintenance.

What does it include?– updating portions of the database– inserting portions of the database– deleting portions of the database

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DQL Language

The data query language (DQL) is used to interrogate the database.

The DQL retrieves, sorts, orders, and presents subsets of the database in response to user queries.

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Learning Objective 4

Create a set of well-structured tables to properly store data in a relational database.

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Basic Requirements of the Relational Data Model

1. Each column in a row must be single valued.

2. Primary keys cannot be null.

3. Foreign keys, if not null, must have values that correspond to the value of a primary key in an other relation.

4. All non-key attributes in a table should describe a characteristic about the object identified by the primary key.

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Anomalies That May Occur in Non-Normalized Relational Tables

Update Anomaly: When changes (updates) to data values are not correctly recorded.Instead of having to update once,

each record in the single table has to be updated individually in order to avoid inconsistencies in the database.

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Anomalies That May Occur in Non-Normalized Relational Tables

Insert Anomaly: There is no way to store information about one entity in the database without it being associated with another entityIn the text, we would not be able to

store information on new customers without their being associated with transactions first!

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Anomalies That May Occur in Non-Normalized Relational Tables

Delete Anomaly: Unintended results arising from deleting a row of data pertaining to one entity and resulting in the deletion of data regarding another entity as well.In the text, if a particular Inventory item were

discontinued and hence removed from the database table, we would lose information on the customer associated with that inventory item as well.

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Approaches to Database Design Normalization

Starts with the assumption that all data is initially stored in a large non-normalized table.

This table is then decomposed using a set of normalization rules to create a set of tables in the Third Normal Form.

Semantic Data Modeling The database designer uses his/her

knowledge about the business structure to create a set of relational tables.

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Database Systems and theFuture of Accounting

Database systems have the potential to significantly alter the nature of external reporting.

Perhaps the most significant effect of database systems will be in the way that accounting information is used in decision making.

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End of Chapter 4