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Title: Introduction to Database Systems
Description: Brief introduction to database, approaches of implementing business event processing, techniques used to design AIS databases, and normalisation.
Description: Brief introduction to database, approaches of implementing business event processing, techniques used to design AIS databases, and normalisation.
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ACW2851 Accounting Information Systems and Financial Modeling
Lecture 7 Introduction to Database Systems
Databases
Modern AISs use databases to:
> Systematically record data, in convenient
& useful formats
...
Contain valuable
information that may
be irreplaceable &
are at "heart" of AISs
...
e
...
Def
...
Importance
Database
Storing data
in databases
Data in an organization's databases must
be stored & organised efficiently
...
Record
Combines related data fields
...
Byte
8 bits create a byte that
represents a character
...
a
...
a
...
Record structures
Record keys
Primary keys
Are unique identifiers to
each record
...
Secondary keys
Are
- non-unique identifiers for records, and
- used for searching files for specific
information
...
Reason: Difficult to ensure data in multiple files are kept up-to-date
...
- Data lacks integrity
Reason: Inconsistent data is capable of supplying incorrect or contradictory
information to its users
...
*Redundant data occurs when you store multiple copies of the same data
...
- Data support the role of programs that run in each application
system
...
Consequence: Data redundancy can cause inconsistencies (poor
integrity/reliability) among the same data in different files (e
...
information is updated in one file, but not the other files)
...
- Facts about business events are stored in relational database
tables instead of separate files
...
- Makes it possible for the creation of integrated business
information systems that include data about all of a company's
operations in one massive collection of relational tables (Enterprise
database)
...
Benefits:
- Redundancy can be reduced
...
- Security restrictions can be applied as data is controlled by DBA centrally
...
Database Management Systems (DBMS)
- Def
...
- DBM integrate a collection of files that are independent of application programs (means can be changed/used by
other applications) & are available to satisfy a number of different processing needs
...
- Provides useful data to managers -> enhances the organisation's management activities
...
o Can recover (if a problem occurs) by:
v Verifying that a problem has happened,
v Reversing whatever entries were made, &
v Starting anew
...
o Log of transaction leaves an audit trail
...
Lost Update Problem: Happens because the files/records was not locked when
multiple users access the files/records
...
•
Backup & Security
− Information in accounting databases must be protected:
o Is stored by backup procedures for retrieval if original copies are lost or
damaged
...
§ Flexible (compared to hierarchical & network database structures)
...
§ Terminology:
o Primary Key (PK): an attribute(s) that uniquely identify a row (record) in a table
...
REA Modeling
§ Used to develop a logical model of the database
...
§ Common accounting entities include:
o Resources – things that the company
owns (assets)
o Events – occurrences related to
resources (or business processes)
o Agents – people/organizations that
participate in business activities
...
Step 3: Create tables showing attributes for each table
o The analyst continues the data modeling process transforming (normalizing) the
data model into a sound logical design for the database
...
4
Lecture 7 Introduction to Database Systems
ACW2851 Accounting Information Systems and Financial Modeling
Relationship
• Relationships between entities are determined by analyzing the system
...
− 1:N or 1:M – one to many; e
...
1 credit sale record can be assigned to 1 customer; 1
customer can have many credit sales
...
g
...
• Some ER diagrams show if a relationship is:
− Mandatory (denoted by a “I”); or
− Optional (denoted by an “O”)
...
1 customer can have many sales
...
A customer may have many sales or none
at all
...
A customer may have many sales or no sales at
all
...
A sale must involve at least one item
...
A goods shipment must have at
least a customer order
...
An A/R clerk may be involve in many payments received
or no payment all
...
A formal process that ensures that each data attribute (field) is attached to the correct table &
promotes accuracy & non-redundant storage of data
...
• Normal forms are inclusive (higher forms include all lower forms)
...
− Failure to normalize results in update anomalies/errors that otherwise might occur when
adding, changing or deleting data stored in the database
...
− Table(s) can be updated with greater efficiency
...
Functional Dependence
An attribute (B) is functionally dependent on another attribute (A), if a value of (A) determines a single
value of (B) at any one time
...
Partial Dependency
Exists when a non-key attribute is functionally dependent on part (but not all) of the private key (PK)
...
g
...
− If EMP_NUM was the PK of the Employee table there would be no need to use both
EMP_NUM and PROJ_NUM to determine EMP_NAME
...
− E
...
CHG_HOUR is dependent on JOB_CLASS
...
To check whether a database table is 3NF:
Apply Codd’s Rule: All non-key attributes should be functionally dependent upon the whole primary
key
...
g
...
− JOB_CLASS invites entry errors (e
...
Elec
...
vs Elect
...
E
...
− Every time an employee is assigned to a project, employee name is repeated
...
First Normal Form (1NF)
A relation is in 1NF if it doesn’t contain repeating groups (a unique PK)
To transform 1NF->2NF
• 2NF must contain no partial dependency
...
g
...
Lecture 7 Introduction to Database Systems 7
ACW2851 Accounting Information Systems and Financial Modeling
Second Normal Form (2NF)
Must contain no partial dependencies
...
• E
...
CHG_HOUR is dependent on JOB_CLASS (JOB_CLASS is not a PK)
...
8
Lecture 7 Introduction to Database Systems
ACW2851 Accounting Information Systems and Financial Modeling
How does Database Management Systems (DBMS) aid decision-making?
• Data stored in DBMS allows opportunities for businesses to understand their business &
customers to aid in decision-making
...
• Data mining
• DSS and MIS (Refer to 1st lecture)
...
Data Warehousing
• An integrated decision support database whose content is derived from various
operational databases
...
• Supports data mining & its design are geared towards the efficient generation of
reports for management
...
features • Deals with achieve data
...
Purpose
Examples
Exploration, aggregation & analysis of large quantities of data from across organization
using multi-dimensional analytical tools
...
• To find hidden patterns & relationships from the data
Title: Introduction to Database Systems
Description: Brief introduction to database, approaches of implementing business event processing, techniques used to design AIS databases, and normalisation.
Description: Brief introduction to database, approaches of implementing business event processing, techniques used to design AIS databases, and normalisation.