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Relational Databases4
UAA – ACCT 316Accounting Information
SystemsDr. Fred Barbee
Ch
ap
ter
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Creating a database can be like creating a universe, only more complicated. At least when the universe was created, there was no one around to complain.
Michael J. Hernandez Database Design for Mere Mortals
Addison Wesley, Boston, 1997
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An Out-of-the-Text Experience!
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Types of Databases
4
Chap
ter
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Types of Databases
Operational Database
Used whenever there is a need to collect, maintain, and modify data.
Stores dynamic data (i.e., the data changes constantly and reflects up-to-the-minute information).
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Types of Databases
Analytical Database
Used to store and track historical and time-dependent data..
Stores static data that is never (or rarely) modified. Information is applicable to a specific point in time.
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Early Database Models
4
Chap
ter
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Hierarchical Database Model
Data is structured hierarchically.
Visualize as an inverted tree.
A single table acts as the “root” of the tree.
Other tables act as branches flowing from the root.
Hierarchical Database Model
Hierarchical Database Model
AgentsAgents
EntertainersEntertainers ClientsClients
ScheduleSchedule PaymentsPaymentsEngagementsEngagements
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Network Database Model
Visualize as an inverted tree.
Several inverted trees may share branches,
All of which are part of the same database structure.
The Network Database ModelThe Network Database Model
AgentsAgents
ClientsClients EntertainersEntertainers
PaymentsPayments Musical Styles
Musical StylesEngagementsEngagements
Represent Manage
Schedule Perform PlayMake
A Basic Set StructureA Basic Set Structure
Rela
tion
sh
ip
Owner Table
Member Table
AgentsAgents
ClientsClients
Set Structure
Rep
resen
t
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Enter . . . The Relational Database Model
Relational Database
Rela
tional D
ata
base
s
Rela
tional D
ata
bases
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Relational Database Model
Data is stored in relations, which are perceived by the user as tables.
Each relation is composed of tuples (records) and attributes (fields).
Fundamental Data Storage Concepts and Definitions
Accounts Receivable File
2 Entities 2 Records
Attributes
Customer Customer Credit number name Address limit Balance
Data values
301 ABC Co. Box 5 1,000 400 555 XYZ Co. Box 96,000 2,000
Individual fields
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Relational Database Model
The physical order of the records of fields in a table is completely immaterial.
Each record in the table is identified by a field that contains a unique value.
A Relational Database ModelA Relational Database Model
AgentsAgents
ClientsClients EntertainersEntertainersMusical Styles
Musical Styles
Entertainer Styles
Entertainer StylesEngagementsEngagements
Agent ID First Name Last Name Hire Date Phone
100 Mike Hernandez 05/16/02 333-4444
101 Greg Piercy 10/15/02 444-3333
Client ID Agent ID First Name Last Name …..
9001 100 Stewart Jamison …..
9002 101 Shannon McClain …..
Agents
Clients
Ent ID Agent ID First Name Last Name …..
3000 100 John Slade …..
3001 101 Mark Weiser …..
Client ID Ent ID Eng. Date Time …..
9001 3001 04/01/02 1-3 PM …..
9002 3002 04/12/02 7-9 PM …..
Entertainers
Engagements
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Now, Back to the Text
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Double-Entry Vs. Database Accounting
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Double-Entry Versus Database Accounting
Luca Pacioli and double-entry accounting.
Captures and stores key attributes of transactions in a highly aggregated form.
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Double-Entry Versus Database Accounting
The beloved debit/credit convention provided an important internal control feature in manual systems.
Enter computerized accounting.
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Double-Entry Versus Database Accounting
The ability to quickly capture lots of data quickly . . .
Date and time of purchase
Identity of item purchased
Store location
Checkout station number
Cashier number
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Double-Entry Versus Database Accounting
Consider a simple transaction:
On November 18, 2002 we made a sale to Jones Enterprises for $10,000 on credit.
Terms 2/10, n/30
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How would we handle this transaction in a double-entry system?
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Files Vs. Databases
4
Chap
ter
Fundamental Data Storage Concepts and Definitions
Accounts Receivable File
2 Entities 2 Records
Attributes
Customer Customer Credit number name Address limit Balance
Data values
301 ABC Co. Box 5 1,000 400 555 XYZ Co. Box 96,000 2,000
Individual fields
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Basic File Types
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.
File-Oriented Approach
Applicationprogram #1
File # 1
Item A Item B Item C
Applicationprogram #2
File # 2
Item B Item D Item E
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How would we handle this transaction in a relational database system.
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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
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Databases
A database is a set of interrelated, centrally coordinated files.
Focus is on
Data integration
Data sharing
Database Approach
Applicationprogram #3
Applicationprogram #2
Databasemanagement
system
Applicationprogram #1
Item A Item B Item C Item D Item E
Database
Database System
Applicationprogram #3
Applicationprogram #2
Databasemanagement
system
Applicationprogram #1
Item A Item B Item C Item D Item E
Database
DBMS refers to programs that control the data and interfaces between the
data and the application programs.
The Data Base Administrator (DBA) is
responsible for the database.
A Database Accounting System
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Advantages & Disadvantages of Relational Database Systems
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Advantages
Reduce data storage costs
Eliminate data redundancy
Eliminate data inconsistencies
Avoid duplicate processing
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Advantages
Ease add, delete, and update data maintenance tasks
Make data independent of applications
Centralize data management
Centralize data security
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Advantages
Ease report modifications and updats
Provide ad hoc query capabilities
Facilitate cross-functional data analysis
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Advantages
Permit multiple users simultaneous data access.
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Disadvantages
Greater hardware requirements
The database software itself
Employing a database administrator.
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Disadvantages
Centralization of data . . .
System operation becomes critical
Incorrect data entry corrupts many users’ work
Territorial disputes over data ownership may arise
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One Last Disadvantage
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It’s Your Turn!
Discussion Question 4.3 p. 99
The text explained how database technology may eliminate the need for double-entry accounting. This creates three possibilities:
The double-entry model will be abandoned,
The double-entry model will not be used directly, but an external-level schema based on the double-entry model will be defined for accountant’s use; or
The double entry model will be retained in database systems.
Which alternative do you think is most likely to occur? Why?
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Logical View
Vs.Physical
View
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Physical View
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Physical View
The physical view refers to how and where the data are physically arranged and stored on disk, tape, CD-ROM, or other media.
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Logical View
The logical view is how the user or programmer conceptually organizes and understands the data.
Logical View Vs. Physical View
Credit Report
Customer NumberCredit Limit
Balance
Monthly Statement
Customer NameAddressBalance
Customer NumberCustomer Name
AddressCredit Limit
Balance
How data are stored
on disk.
Logical View Data Physical View
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Schemas
4
Chap
ter
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Schemas
A schema describes the logical structure of a database.There are three levels:
Conceptual-LevelExternal-LevelInternal-level
Conceptual-Level Schema
An organization-wide view of the entire database.
External-Level Schema
Consists of a set of individual user views of portions of the database, also referred to as a subschema.
Internal-Level Schema
The internal-level schema provides a low-level view of the database.
Database Management System
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DBMS Languages
4
Chap
ter
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DBMS Languages
Every DBMS must provide a means of performing the three basic functions:
Creating the database
Changing the database
Querying the database
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Data Definition Language (DDL)
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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Data Manipulation Language (DML)
Used for data maintenance.
updating portions of the database
inserting portions of the database
deleting portions of the database
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Data Query Language (DQL)
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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More on the Relational Data Model
4
Ch
ap
ter
Table in a Relational Data Model
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Basic Requirements of the Relational Data Model
Primary keys must be unique.
The primary key cannot be null (blank).
Why?
Known as the entity integrity rule.
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What is the entity integrity rule?
The entity integrity rule ensures that every row in every relation (table) must represent data about some specific object in the real world.
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Basic Requirements of the Relational Data Model
Every foreign key must either be null or have a value corresponding to the value of a primary key in another relation.
Why?
The referential integrity rule.
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What is the referential integrity rule?
The referential integrity rule ensures that links exist among the tables of a database.
Basic Relational Data Model Stuff
Relation = Table = File
Some terminology
Table in a Relational Data Model
Tuple = Row = Record
Some terminology
Table in a Relational Data Model
Attribute = Column = Field
Some terminology
Attribute = Column = Field
Each column in a table must describe a characteristic of the object identified by the primary key.
Attribute = Column = Field
Each attribute (column) in a table has a distinct name, called the attribute name.
Attribute = Column = Field
Every entry in a column contains a value for that column only, and the values are of the same data type.
Attribute = Column = Field
The order (position) of the columns in relation to each other is unimportant.
Tuple = Row = Record
The entries in each column of any row must be single valued.
Tuple = Row = Record
The order of the rows is unimportant.
Tuple = Row = Record
Each row is unique; it differs from all other rows in the table.
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How does a database
differ from a spreadsheet
?
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How might an accountant’s
familiarity with the tabular
representation of spreadsheets
facilitate or hinder learning how to use a relational DBMS?
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Importance of a Well-Structured Relational Database
4
Ch
ap
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Anomalies that may occur in non-normalized relational tables.
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Normalization! Anomalies! WOW! You accountants are an odd lot!
What is normalization? Is anything normal
around here?
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Normalization
A technique used to make complex databases more efficient by removing undesirable redundancy.
Break one large table into several smaller tables.
Normalization
Normalization starts with the assumption that everything is initially stored in one large table.
A set of rules is then followed to decompose that initial table into a set of normalized tables.
The objective is to produce a set of tables that are in what is called third normal form (3NF)
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Normalization
Problems caused by redundancy:
Storage inefficiencies
Processing inefficiencies
Errors
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Update Anomaly
When changes (updates) to data values are not correctly recorded.
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Insert Anomaly
There is no way to store information about one entity in the database without it being associated with another entity
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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.
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Database Design
4
Ch
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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.
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Approaches to Database Design
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 Design Objectives
Completeness
Relevance
Accessibility
Up-to-dateness flexibility
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Database Design Objectives
Efficiency
Cost-effectiveness
Integrity
Security
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Database Systems and theFuture of Accounting
Database systems have the potential to significantly alter the nature of external reporting.
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Database Systems and theFuture of Accounting
Perhaps the most significant effect of database systems will be in the way that accounting information is used in decision making.
