Transcript Principles of Information Systems

DATA MODELING
SECTION 3
Data Modeling constructs.
Structured Methodologies
• The techniques are instructions that are
carefully drawn up, often step-by-step, with
each step building on the previous step.
• Progresses from the highest level of
abstraction to the lowest level of detail
• General to the specific
Methodologies
• Include:
• structured analysis, structured design, and structured
programming
Structured Analysis
• Widely used top-down approach
• Primary tool is?
Data Flow Diagrams
• Graphically illustrates a system’s
component processes and the flow of data
between them
• Four basic symbols
1
2
3
4
Data Flow
Process
Data store
Source/Sink
Context Diagram Example
• An overview DFD of the entire system as a single
process. Shows major inputs and outputs
Employee
Benefits
statements
Earnings
Payroll
Dept
Hours-worked
Employee Beneficiary
Changes designation
Pension benefits
recordkeeping
system
Actuary factors
Actuary
Zero-Level DFD
Benefits statement
Payroll
Dept.
Employee
Employee
changes
Earnings
Hours
worked
Beneficiary
designation
2.0
Track
credited
service
1.0
Track
participation
3.0
Capture
Earnings
Credited
service
Eligibility
Pensionable earnings
Actuary
factors
Benefits master file
Survivor option
Pension benefit
5.0
Calculate
benefit
Retirement dates
Pensionable-earnings history
4.0
Maintain
actuary
tables
Actuarial formula
Actuarial table
Actuary formula
System
Boundary
Actuary
First-Level DFD
Actuarial formula
Actuarial formula
Actuarial file
Final average earnings
5.1
Calculate
final average
earnings
5.2
Calculate
normal
retirement
benefit
Normal retirement
benefit
Early
retirement
option date
Normal
retirement
option date
5.3
Retirement benefits
Calculate early
retirement
benefit
Retirement
benefits
Benefits master file
Pensionable
earnings history
Employee details
5.5
Generate
benefits
statement
Benefits statement
5.4
Calculate
survivor
benefit
Survivor
Benefit
Structured Design
• Encompasses a set of design rules and
techniques for designing a system from the
top down in a hierarchy
Structure Chart
• consider the main function, then break it
down into sub-functions
High-Level Structure Chart
Process
payroll
Get valid
inputs
Get
inputs
Validate
inputs
Calculate
pay
Calculate
gross pay
Calculate
net pay
Write
outputs
Update
master file
Write checks,
reports, and
output files
Structured Programming
• Extends the principles governing structured
design to the writing of programs.
• Incorporate the concepts of modularity
• Sequence construct
– executes statements in the order in which they
appear
• Selection construct
– tests a condition and executes one of two or
more alternatives
• Iteration construct
– repeats an instruction as lon as the results of a
conditional test remain true
Basic Control Structures
A
Sequence
B
Action A then Action B
S
Selection
If Condition = S Then do Action C
C
D
Else do Action D
Endif
Iteration
E
Do While Condition = R
Action E
Enddo
R
The Entity-Relationship Model
• Introduced by Peter Chen in 1976
• Part of a number of Case tools
• Key elements
– entities, attributes, identifiers, and relationships
Entities
• Something that can be identified in the
users’ work environment
• Entity classes
Attributes
• Describe the entity’s characteristics
CUSTOMER
CustNumber
CustName
Address
City
Province
PostalCode
ContactName
PhoneNumber
Primary Key?
Two instances of CUSTOMER
12345
Ajax Manufacturing
123 Elm St
Toronto
Ont
J1K6F9
P. Shwartz
223-5567
67890
Jefferson Dance Club
345 Main St East
Hamilton
Ont
L8P1R5
Frita Bellingsley
545-1267
Identifiers
• Attributes that name or identify entity
instances
• Unique vs. Non-unique
• Composite identifiers
Relationships
• The way entities can be associated with one
another
• Degree of relationship
SALESPERSON
MOTHER
FATHER
SP-ORDER
PARENT
ORDER
CHILD
• Binary relationships
– Relationships of degree 2
– Three type of binary relationships
• 1:1, 1:N,
EMPLOYEE
DORMITORY
STUDENT
N:M
1
1
M
has
has
has
1
N
N
COMPANY CAR
STUDENT
CLUB
• Cardinality
RESIDENCE
1
(0,400)
has
N
(1,1)
STUDENT
Optional Entity
Optional existence
STUDENT
1
takes
N
COURSE
• Recursive relationship
STUDENT
rooms
with
Showing Attributes in an ERD
• Ellipses or flag
CustomerNumber
CustomerAddress
CustomerName
CustomerNumber
CustomerAddress
CustomerName
CUSTOMER
CUSTOMER
Weak Entities
• Cannot exist in the database unless another
type of entity exists
EMPLOYEE
PATIENT
1
1
has
has
M
M
DEPENDENT
PRESCRIPTION
ID-Dependent Entities (special type of weak entity)
• One in which the identifier of one entity
includes the identifier of another entity
BUILDING
1
has
M
APPARTMENT
EXOTIC RV RENTALS
Exotic RV Rentals is an agent that rents recreational vehicles to customers for a fee.
Exotic does not own any RVs but instead leases or rents them on behalf of the RV owner
who wishes to earn income when they are not using their RV. Exotic charges a fee for its
service. Exotic specializes in RVs that can be used for multi-day, weekly, or monthly
rentals. The smallest RV in their inventory is 20 feet and the largest is 40 feet.
Each RV is fully equipped at the time it is rented. Most of the equipment is provided
by the owners, but some is added by Exotic. The owner-provided equipment includes what
is fixed on the RV, such as radio, stoves, tables, beds, generators, and refrigerators. Other
owner-provided equipment is not installed as part of the RV. Such equipment includes
dishes, silverware, cooking utensils, bedding, and the like. Exotic provides consumable
equipment, which could also be considered supplies, such as maps, soap, dish towels, toilet
paper, and similar items.
An important part of Exotic’s responsibilities is keeping track of the equipment on the
RV. Some of it is expensive, and some of it, particularly what is not attached to the RV, can
be easily lost or stolen. Customers are responsible for all equipment during the period of
their charter.
Exotic likes to keep accurate records of its customers and the rentals, not only for
marketing but also for recording the trips that customers have taken. Some trips can have
poor weather conditions or interesting places and Exotic like to know which customers
have what experience.
RVs often need maintenance. Exotic is required by its contracts with the RV owners to
keep accurate records of all maintenance activities and costs, including normal activities,
such as cleaning or engine-oil changes, and unscheduled repairs. In some cases, repairs are
necessary during a rental. An engine, for example, might require maintenance while the
RV is far away from Exotic’s facility. In this case, the customers phone the Exotic
dispatcher, who determines the best facility to make the repair and phones the repair
facility so that they can go to the customers aid. To make these decisions, the dispatchers
need information about repair facilities as well as past histories of repair quality and cost.
Possible Entities for Exotic
• What should one look for?
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RENTAL
LEASE
RV
CUSTOMER
OWNER
EQUIPMENT
OWNER-PROVIDED-EQUIPMENT
FIXED-OWNER-EQUIPMENT
REMOVABLE-OWNER-EQUIPMENT
EXOTIC-PROVIDED-EQUIPMENT
ITINERARY/WEATHER
SCHEDULED-MAINTENANCE
UNSCHEDULED-MAINTENANCE
REPAIRS
REPAIR-FACILITY
Selected Entities for Exotic for ERD
• Some entities may not be needed
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RENTAL or LEASE (synonyms)
RV
CUSTOMER
OWNER
EQUIPMENT
ITINERARY/WEATHER
SCHEDULED-MAINTENANCE
REPAIRS or UNSCHEDULED-MAINTENANCE (synonyms)
REPAIR-FACILITY
The ERD
SCHEDULEDMAINTENANCE
OWNER
N:M
1:N
N:M
RV
EQUIPMENT
REPAIR
1:N
1:N
N:M
Note: Not the only
model possibility!
RENTAL
N:1
CUSTOMER
1:1
WEATHERITINERARY
Models
• There are a variety of different ways of
modeling a particular situation
• Evaluating alternatives
• Does model accurately reflect the users
needs and ways of doing things?
REA Model
• An Accounting Model
• Resources, Events & Agents
• Resource?
• Event?
• Agent?