DATABASE MANAGEMENT

Charlene E. Matubis BSA-IIIAccounting Information Systems

Chapter 9 Reporting

Two Components of Computer Processing

1. Data2. Instructions (programs)

Two methods for designing interface between programs and data:

1. File-oriented (flat-file) processing: A specific data file was created for each application [legacy systems]

2. Data-oriented processing: Create a single data repository to support numerous applications [current systems]

FLAT FILE ENVIRONMENT

DATABASE APPROACH

ADVANTAGES AND DISADVANTAGES OF THE TWO METHODS

Flat-File Problems( Data Redundancy)

Data Storage - creates excessive storage costs of paper documents and/or magnetic formData Updating - any changes or additions must be performed multiple times Currency of Information - potential problem of failing to update all affected filesTask-Data Dependency - user’s inability to obtain additional information as his or her needs change

Advantages of the Database Approach

Data sharing/centralized database resolves flat-file problems:

No data redundancy - Data stored only once, eliminating data redundancy and reducing storage costs.Single update - Because data are in only one place, requires only single update procedure, reducing time/cost of keeping database current.Current values - Change to database made by any (authorized) user yields current data values for all other (authorized) users.Task-data independence - As users’ information needs expand beyond immediate domain, new needs can be more easily satisfied than under flat-file approach.

Disadvantages of the Database Approach

Can be costly to implement additional hardware, software, storage, and network

resources are required – yet these costs continue to drop…

Can only run in certain operating environments may be unsuitable for some existing system

configurations (e.g., legacy systems)

WHAT IS DBMS?

Database management system

Purpose of DBMS is to provide controlled access to database.

DBMS is special software programmed to know which data elements each user is authorized to access and deny unauthorized requests of data.

Three Steps in Designing a Database

1. Prepare conceptual modelIdentify entitiesIdentify relationships between

entitiesPrepare ER diagram (ERD)

Samply Entity Relationship Diagram

2. Specify logical design Select logical database model (which

will always be relational nowadays) Transform conceptual data model using

logical database model

3. Implement physical design

Physical structuresAccess methods

What is the Logical Data Structures?

Logical Data StructuresObjective is to develop structure efficiently so data can be accessed quickly and easily.

Four types of database structures are: hierarchical (tree structure) network relational object-oriented

The Relational Model

Relational model portrays data in form of two dimensional tables (looks like Excel worksheet)

relation - database table attributes/fields (data elements) -

columns tuples (records) - rows data - intersection of rows and columns

Anomalies in Database

Three Types of Anomalies

(Anomalies are found in unnormalized tables)

Insertion Anomaly: New item cannot be added to table until at least one entity uses particular attribute item.Deletion Anomaly: If attribute item used by only one entity is deleted, all information about that attribute item is lost.Update Anomaly: Modification on attribute must be made in each of rows in which attribute appears.(Anomalies can be corrected by creating relational tables)

How to prevent?Through Relational Tables and Normalization ProcessVarious items of interest (customers, inventory, sales) stored in SEPARATE tables in database.Advantages:

Removes all three anomalies Efficient use of space. Flexible. Users can form ad hoc relationships

for queries.

Normalization ProcessProcess that breaks up large, complex tables into smaller tables that meet two conditions:

all nonkey attributes (fields) in table are dependent on primary key (PK)

all nonkey attributes (fields) are independent of other nonkey attributes (fields)

When unnormalized tables are split and reduced to third normal form, they are linked together by foreign keys (secondary keys).

Steps in Normalization

First normalform (1NF)

Second normalform (2NF)

Third normalform (3NF)

1. Remove

repeatinggroups

2. Remove partial

dependencies

3. Removetransitive

dependencies

Does field depend on PK? If no, remove and put in another table.

Only concerns tables with composite PKs.

When field depends on another non-key field in table.

Accountants and Data Normalization

1. Update anomalies can generate conflicting and obsolete database values.2. Insertion anomalies can result in unrecorded transactions and incomplete audit trails.3. Deletion anomalies can cause loss of accounting records and destruction of audit trails.

“Accountants should understand data normalization process and be able to determine whether

database is properly normalized.”

DDP VS CDP

Distributed Data Processing

Disadvantages Loss of control (organization-wide) Mismanagement of organization-wide resources Hardware/software incompatibility Redundant tasks/data Incompatible tasks may be consolidated Lack of standards

Advantages: Cost reductions in hardware and data entry tasks Improved cost control responsibility Improved user satisfaction because control is closer

to user level Backup of data can be improved through use of

multiple data storage sites

Centralized Data Processing

Data are retained in central location. Remote IPUs (workstations) send requests for data.Central site services needs of remote workstations.Actual data processing is performed at remote workstation

Deadlock Phenomenon Especially a problem with partitioned

databases Occurs when multiple sites lock each

other out of data that they are currently using

Special software needed to analyze and resolve conflicts.

SAMPLE DATABASES

Enrollment System

PAYROLL SYSTEM

Accounting Department