ch04 relational db & REA datamodel Cost allocation for supporting departments and accounting for Joint product and Byproduct .ppt

© 2008 Prentice Hall Business Publishing Accounting Information Systems, 11/e Romney/Steinbart 1 of 96
C HAPTER 4
Relational Databases

INTRODUCTION
• Relational databases underlie most modern integrated
AISs.
– They are the most popular type of database used
for transaction processing.
– In this chapter, we’ll define the concept of a
database.

File Vs. Databases
• Database systems were developed to address the problems
associated with the proliferation of master files.
– For years, each time a new information need arose,
companies created new files and programs.
– The result: a significant increase in the number of
master files.

FILE VS. DATABASES
• This proliferation of master files created
problems:
– Often the same information was stored in
multiple master files.
– Made it more difficult to effectively integrate
data and obtain an organization-wide view of
the data.
– Also, the same information may not have been
consistent between files.
• If a student changed his phone number, it
may have been updated in one master file
but not another.
Master File 1
Fact A
Fact B
Fact C
Master File 2
Fact A
Fact D
Fact F
Master File 1
Fact A
Fact B
Fact F
Enrollment
Program
Financial Aid
Program
Grades
Program

FILE VS. DATABASES
• A database is a set of inter-
related, centrally coordinated
files.
Database
Fact A Fact B
Fact C Fact D
Fact E Fact F
Enrollment
Program
Financial Aid
Program
Grades
Program
Database
Management
System

FILE VS. DATABASES
• The database approach treats data
as an organizational resource that
should be used by and managed
for the entire organization, not
just a particular department.
• A database management system
(DBMS) serves as the interface
between the database and the
various application programs.
Database
Fact A Fact B
Fact C Fact D
Fact E Fact F
Enrollment
Program
Financial Aid
Program
Grades
Program
Database
Management
System

FILE VS. DATABASES
• The combination of the sdatabase,
the DBMS, and the application
program that access the database
is referred to as the database
system.
Database
Fact A Fact B
Fact C Fact D
Fact E Fact F
Enrollment
Program
Financial Aid
Program
Grades
Program
Database
Management
System

FILE VS. DATABASES
• The person responsible for the database is
the Database Administrator.
• As technology improves, many large
companies are developing very large
databases called Data Warehouses.
Database
Fact A Fact B
Fact C Fact D
Fact E Fact F
Enrollment
Program
Financial Aid
Program
Grades
Program
Database
Management
System

Importance And Advantages Of Database Systems
• As accountants, you are likely to audit or work for companies that use
database technology to store, process, and report accounting
transactions.
– Many accountants work directly with databases and will enter,
process, and query databases.
– Some will develop and evaluate internal controls necessary to
ensure database integrity.
– Others will be involved in the design and management of
databases.

IMPORTANCE AND ADVANTAGES OF
DATABASE SYSTEMS
• Database technology provides the following benefits to
organizations:
– Data integration
• Achieved by combining master files into larger
pools of data accessible by many programs.

IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS
organizations:
– Data sharing
• It’s easier to share data that’s integrated—the FBI is planning an 8
year, $400 million database project to make data more available to
agency users.

organizations:
– Data sharing
– Reporting flexibility
• Reports can be revised easily and generated as needed.
• The database can easily be browsed to research
problems or obtain detailed information.

organizations:
– Data sharing
– Minimal data redundancy and inconsistencies
• Because data items are usually stored only once.

organizations:
– Data sharing
– Data independence
• Data items are independent of the programs that use them.
• Consequently, a data item can be changed without changing the program
and vice versa.
• Makes programming easier and simplifies data management.

IMPORTANCE AND ADVANTAGES OF
DATABASE SYSTEMS
• Database technology provides the
following benefits to organizations:
– Data sharing
– Central management of data
• Data management is more efficient
because the database administrator is
responsible for coordinating, controlling,
and managing data.

• Database technology provides the following benefits
to organizations:
– Data sharing
– Central management of data
– Cross-functional analysis
• Relationships can be explicitly defined and used in
the preparation of management reports.
• Example: relationship between selling costs and
promotional campaign's.

Database Systems
• Logical and physical views of data
– In file-oriented systems, programmers must know the physical
location and layout of records used by a program.
• They must reference the location, length, and format of every
field they utilize.
• When data is used from several files, this process becomes
more complex.

Database Systems
• Database systems overcome this problem by separating the
storage and use of data elements.
– Two separate views of the data are provided:
• Logical view
 How the user or programmer conceptually organizes
and understands the data.

Database Systems
• Database systems overcome this problem by
separating the storage and use of data elements.
• Logical view
• Physical view
 How and where the data are physically arranged and
stored.

DATABASE SYSTEMS
• Database systems overcome this problem by separating the storage and use
of data elements.
• Logical view
• Physical view
– Separating these views facilitates application development, because
programmers can focus on coding the logic and not be concerned
with storage details.

Database
Logical View—User A Logical View—User B
DBMS
Operating
System
The DBMS translates users’ logical
views into instructions as to which
data should be retrieved from the
database.
Enrollment by Class
Scholarship Distribution
Fr.
5%
Soph.
24%
Jr.
38%
Sr.
33%

Database
Enrollment by Class
Logical View—User A Logical View—User B
DBMS
Operating
System
The operating system translates
DBMS requests into instructions to
physically retrieve data from
various disks.
Scholarship Distribution
Fr.
5%
Soph.
24%
Jr.
38%
Sr.
33%

Database Systems
• The DBMS handles the link between the physical and
logical views of the data.
– Allows the user to access, query, and update data
without reference to how or where it is physically stored.
– The user only needs to define the logical data
requirements.

Database Systems
• Schemas
– A schema describes the logical structure of a database.
– There are three levels of schema.
• Conceptual level
• The organization-wide view of the entire database i.e. the big
picture.
• Lists all data elements and the relationships between them.

Subschema--User A Subschema--User B Subschema--User C
Student Record Class Record
Student No. --character [9] Class Name --character [9]
Student Name --character [26] Dept No. --integer [4], non-null, index=itemx
SAT Score --integer [2], non-null, index=itemx Course No. --integer [4], non-null, index=itemx
Enroll
Cash
Receipt
Classes Student
Mapping external-level views to conceptual-level schema
Mapping conceptual-level items to internal-level descriptions
Smith . . . A
Jones . . . B
Arnold . . .D

DATABASE SYSTEMS
• Schemas
• External level
• A set of individual user views of portions of the database, i.e., how each user
sees the portion of the system with which he interacts.
• These individual views are referred to as subschema.

Enroll
Cash
Receipt
Classes Student
Smith . . . A
Jones . . . B
Arnold . . .D

DATABASE SYSTEMS
• Schemas
• External level
• Internal level
• A low-level view of the database.
• It describes how the data are actually
stored and accessed including:
– Record layouts
– Definitions
– Addresses
– Indexes

Enroll
Cash
Receipt
Classes Student
Smith . . . A
Jones . . . B
Arnold . . .D

Database Systems
• Accountants are frequently involved in developing
conceptual- and external-level schema.
• An employee’s access to data should be limited to
the subschema of data that is relevant to the
performance of his job.

Database Systems
• The data dictionary
– A key component of a DBMS is the data dictionary.
• Contains information about the structure of the
database.
• For each data element, there is a corresponding
record in the data dictionary describing that element.

Database Systems
• Information provided for each element includes:
– A description or explanation of the element.
– The records in which it is contained.
– Its source.
– The length and type of the field in which it is stored.
– The programs in which it is used.
– The outputs in which it is contained.
– The authorized users of the element.
– Other names for the element.

DATABASE SYSTEMS
 Accountants should participate in the
development of the data dictionary because they
have a good understanding of the data elements
in a business organization, as well as where
those elements originate and how they are used.

DATABASE SYSTEMS
• DBMS Languages
–Every DBMS must provide a means of
performing the three basic functions of:
• Creating a database
• Changing a database
• Querying a database

DATABASE SYSTEMS
• Creating a database:
– The set of commands used to create the
database is known as data definition
language (DDL). 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 records or fields

DATABASE SYSTEMS
• Changing a database
– The set of commands used to change the
database is known as data manipulation
language (DML). DML is used for
maintaining the data including:
• Updating data
• Inserting data
• Deleting portions of the database

DATABASE SYSTEMS
• Querying a database:
– The set of commands used to query the database is
known as data query language (DQL). DQL is used
to interrogate the database, including:
• Retrieving records
• Sorting records
• Ordering records
• Presenting subsets of the database
– The DQL usually contains easy-to-use, powerful
commands that enable users to satisfy their own
information needs.

DATABASE SYSTEMS
• Report Writer
– Many DBMS packages also include a report writer, a
language that simplifies the creation of reports.
– Users typically specify:
• What elements they want printed
• How the report should be formatted
– The report writer then:
• Searches the database
• Extracts specified data
• Prints them out according to specified format

RELATIONAL DATABASES
• A DBMS is characterized by the type of
logical data model on which it is based.
– A data model is an abstract representation of
the contents of a database.
– Most new DBMSs are called relational
databases because they use the relational
model developed by E. F. Codd in 1970.

• The relational data model represents
everything in the database as being stored
in the forms of tables (aka, relations).

Student ID
Last
Name
First
Name
Phone
No.
333-33-3333 Simpson Alice 333-3333
111-11-1111 Sanders Ned 444-4444
123-45-6789 Moore Artie 555-5555
STUDENTS
Course ID Course Section Day Time
1234 ACCT-3603 1 MWF 8:30
1235 ACCT-3603 2 TR 9:30
1236 MGMT-2103 1 MW 8:30
COURSES
Relation
SCID Student ID Course
333333333-1234 333-33-3333 1234
333333333-1236 333-33-3333 1236
111111111-1235 111-11-1111 1235
111111111-1236 111-11-1111 1235
STUDENT x COURSE

• This model only describes how the data
appear in the conceptual- and external-
level schemas.
• The data are physically stored according
to the description in the internal-level
schema.

Student ID
Last
Name
First
Name
Phone
No.
333-33-3333 Simpson Alice 333-3333
111-11-1111 Sanders Ned 444-4444
123-45-6789 Moore Artie 555-5555
STUDENTS
1234 ACCT-3603 1 MWF 8:30
1235 ACCT-3603 2 TR 9:30
1236 MGMT-2103 1 MW 8:30
COURSES
A primary key is the
attribute or combination
of attributes that
uniquely identifies a
specific row in a table.
STUDENT x COURSE
SCID
333333333-1234
333333333-1236
111111111-1235
111111111-1236

STUDENT x COURSE
SCID
333333333-1234
333333333-1236
111111111-1235
111111111-1236
Student ID
Last
Name
First
Name
Phone
No.
333-33-3333 Simpson Alice 333-3333
111-11-1111 Sanders Ned 444-4444
123-45-6789 Moore Artie 555-5555
STUDENTS
1234 ACCT-3603 1 MWF 8:30
1235 ACCT-3603 2 TR 9:30
1236 MGMT-2103 1 MW 8:30
COURSES
In some tables, two or more attributes
may be joined to form the primary key.

ADVISORS
Advisor No. Last Name First Name Office No.
1418 Howard Glen 420
1419 Melton Amy 316
1503 Zhang Xi 202
1506 Radowski J.D. 203
STUDENTS
Student ID Last Name
First Nam
e Phone No.
Advisor N
o.
333-33-3333 Simpson Alice 333-3333 1418
111-11-1111 Sanders Ned 444-4444 1418
123-45-6789 Moore Artie 555-5555 1503
A foreign key is an attribute in one table that is a primary key in
another table.
Foreign keys are used to link tables together.

ADVISORS
1419 Melton Amy 316
1503 Zhang Xi 202
Other non-key attributes in each table store important
information about the entity.
STUDENTS
First Nam
e Phone No.
Advisor N
o.
333-33-3333 Simpson Alice 333-3333 1418
111-11-1111 Sanders Ned 444-4444 1418
123-45-6789 Moore Artie 555-5555 1503

• Alternatives for storing data
– One possible alternate approach would be to
store all data in one uniform table.
– For example, instead of separate tables for
students and classes, we could store all data
in one table and have a separate line for each
student x class combination.

Student ID
Last Nam
e
First
Name Phone No. Course No. Section Day Time
333-33-3333 Simpson Alice 333-3333 ACCT-3603 1 M 9:00 AM
333-33-3333 Simpson Alice 333-3333 FIN-3213 3 Th 11:00 AM
333-33-3333 Simpson Alice 333-3333 MGMT-3021 11 Th 12:00 PM
111-11-1111 Sanders Ned 444-4444 ACCT-3433 2 T 10:00 AM
111-11-1111 Sanders Ned 444-4444 MGMT-3021 5 W 8:00 AM
111-11-1111 Sanders Ned 444-4444 ANSI-1422 7 F 9:00 AM
123-45-6789 Moore Artie 555-5555 ACCT-3433 2 T 10:00 AM
123-45-6789 Moore Artie 555-5555 FIN-3213 3 Th 11:00 AM
• Using the suggested approach, a student taking three classes
would need three rows in the table.
• In the above, simplified example, a number of problems arise.

Student ID
Last Nam
e
First
• Suppose Alice Simpson changes her phone number. You need to
make the change in three places. If you fail to change it in all three
places or change it incorrectly in one place, then the records for
Alice will be inconsistent.
• This problem is referred to as an update anomaly.

Student ID
Last Nam
e
First
• What happens if you have a new student to add, but he hasn’t
signed up for any courses yet?
• Or what if there is a new class to add, but there are no students
enrolled in it yet? In either case, the record will be partially blank.
• This problem is referred to as an insert anomaly.

Student ID
Last Nam
e
First
• If Ned withdraws from all his classes and you eliminate all three of
his rows from the table, then you will no longer have a record of
Ned. If Ned is planning to take classes next semester, then you
probably didn’t really want to delete all records of him.
• This problem is referred to as a delete anomaly.

STUDENT x COURSE
SCID
333333333-1234
333333333-1236
111111111-1235
111111111-1236
Student ID
Last
Name
First
Name
Phone
No.
333-33-3333 Simpson Alice 333-3333
111-11-1111 Sanders Ned 444-4444
123-45-6789 Moore Artie 555-5555
STUDENTS
1234 ACCT-3603 1 MWF 8:30
1235 ACCT-3603 2 TR 9:30
1236 MGMT-2103 1 MW 8:30
COURSES
• The solution to the preceding problems
is to use a set of tables in a relational
database.
• Each entity is stored in a separate table,
and separate tables or foreign keys can
be used to link the entities together.

• Basic requirements of a relational database
– Every column in a row must be single valued.
• In other words, every cell can have one and only
one value.
• In the student table, you couldn’t have an attribute
named “Phone Number” if a student could have
multiple phone numbers.
• There might be an attribute named “local phone
number” and an attribute named “permanent
phone number.”
• You could not have an attribute named “Class” in
the student table, because a student could take
multiple classes.

• Basic requirements of a relational
database
– The primary key cannot be null.
• The primary key uniquely identifies a specific row
in the table, so it cannot be null, and it must be
unique for every record.
• This rule is referred to as the entity integrity rule.

STUDENT x COURSE
SCID
333333333-1234
333333333-1236
111111111-1235
111111111-1236
Student ID
Last
Name
First
Name
Phone
No.
333-33-3333 Simpson Alice 333-3333
111-11-1111 Sanders Ned 444-4444
123-45-6789 Moore Artie 555-5555
STUDENTS
1234 ACCT-3603 1 MWF 8:30
1235 ACCT-3603 2 TR 9:30
1236 MGMT-2103 1 MW 8:30
COURSES
• Note that within each table, there are no
duplicate primary keys and no null
primary keys.
• Consistent with the entity integrity rule.

database
– A foreign key must either be null or
correspond to the value of a primary key in
another table.
• This rule is referred to as the referential integrity
rule.
• The rule is necessary because foreign keys are
used to link rows in one table to rows in another
table.

ADVISORS
1419 Melton Amy 316
1503 Zhang Xi 202
STUDENTS
First Nam
e Phone No.
Advisor N
o.
333-33-3333 Simpson Alice 333-3333 1418
111-11-1111 Sanders Ned 444-4444 1418
123-45-6789 Moore Artie 555-5555 1503
Advisor No. is a foreign key in the STUDENTS table. Every
incident of Advisor No. in the STUDENTS table either matches
an instance of the primary key in the ADVISORS table or is null.

database
– All non-key attributes in a table should
describe a characteristic of the object
identified by the primary key.
• Could nationality be a non-key attribute in the
student table?
• Could advisor’s nationality be a non-key attribute
in the student table?

• There are two basic ways to design well-
structured relational databases.
– Normalization
– Semantic data modeling

• Normalization
– Starts with the assumption that everything is
initially stored in one large table.
– A set of rules is followed to decompose that
initial table into a set of normalized tables.
– Objective is to produce a set of tables in third-
normal form (3NF) because such tables are
free of update, insert, and delete anomalies.
– Approach is beyond the scope of this book
but can be found in any database textbook.

• There are two basic ways to design well-
structured relational databases.
– Normalization
– Semantic data modeling

• Semantic data modeling (covered in REA
datamodel)
– Database designer uses knowledge about
how business processes typically work and
the information needs associated with
transaction processing to draw a graphical
picture of what should be included in the
database.
– The resulting graphic is used to create a set
of relational tables that are in 3NF.

DATABASE SYSTEMS AND THE FUTURE
OF ACCOUNTING
• Accountants must become knowledgeable
about databases so they can participate in
developing the AIS of the future.
• They must help ensure that adequate
controls are included to safeguard the data
and assure its reliability.

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