Transcript Accounting Information Systems 9th Edition

Accounting
Information
Systems
9th Edition
Marshall B. Romney
Paul John Steinbart
©2003 Prentice Hall Business Publishing,
Accounting Information Systems, 9/e, Romney/Steinbart
4-1
Relational
Databases
Chapter 4
©2003 Prentice Hall Business Publishing,
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4-2
Learning Objectives
1.
2.
3.
4.
Explain the difference between database
and file-based legacy systems.
Describe what a relational database is and
how it organizes data.
Explain the difference between logical and
physical views of a database.
Create a set of well-structured tables to
properly store data in a relational
database.
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Introduction

Ashton Fleming, the accountant for
S&S, believes that the best way to
provide Susan Gonzalez and Scott
Perry 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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Databases


1
2
For many years, companies created new
files and programs each time an information
need arose.
This proliferation of master files created
problems:
Often the same data was stored in two or
more separate files.
The specific data values stored in the
different files were not always consistent.
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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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Types of Files

1
2
Two basic types of files are used to
store data.
The master file, which is conceptually
similar to a ledger in a manual
system.
The transaction file, which is
conceptually similar to a journal in a
manual system.
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Fundamental Data Storage
Concepts and Definitions
Accounts Receivable File
Attributes
Customer Customer
Credit
number name Address limit Balance
301
ABC Co. Box 5 1,000 400
555
XYZ Co. Box 9 6,000 2,000
2 Entities
2 Records
Individual fields
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Data
values
4-11
File-Oriented Approach
File # 1
Item A
Item B
Item C
Application
program #1
File # 2
Item B
Item D
Item E
Application
program #2
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Database Approach
Application
program #1
Database
Item A
Item B
Item C
Item D
Item E
Database
management
system
Application
program #2
Application
program #3
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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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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 Physical
Views 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 Physical
Views 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 Physical
Views of Data
Logical View User A
Logical View User B
Past Due Accounts
Name Balance Days
Jones 2100 50
Perez 1000 60
Sales by Region
database
DBMS
Operating
system
Logical and Physical
Views of Data
What is program-data independence?
 It is the separation of the logical and
physical views of data.

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Schemas
What are schemas?
 A schema describes the logical
structure of a database.
 There are three levels of schemas:

1
2
3
Conceptual-level schema
External-level schema
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
Subschema A
Jones 210
Perez 100
Subschema
B
r
Subschema
C
r
xxxxxxx
xxxxxxx
Mapping external level views to conceptual level schema
Inventory
Sales
Cash receipt
Customer
Schemas
Inventory
Sales
Customer
Cash receipt
Mapping conceptual level items to internal level
descriptions
Inventory Record
Item number – integer (5), non-null, index = itemx
Description – character (15)
The Data Dictionary

What is a data dictionary?


It 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
2
3

Creating the database
Changing the database
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
2
3
Primary keys must be unique.
Every foreign key must either be null
or have a value corresponding to the
value of a primary key in another
relation.
Each column in a table must describe
a characteristic of the object identified
by the primary key.
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Basic Requirements of the
Relational Data Model
4
5
6
Each column in a row must be singlevalued.
The value in every row of a specific
column must be of the same data
type.
Neither column order nor row order is
significant.
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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 entity

In the text, we would not be able to
store information on new customers
without they 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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Database Design Objectives
Completeness
 Relevance
 Accessibility
 Up-to-dateness flexibility
 Efficiency
 Cost-effectiveness
 Integrity
 Security

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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 the
Future 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
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