CS 5150
Software Engineering
Lecture 14
System Architecture 2
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Administration
Second assignment
• Everybody who presented last week should have
received comments on their presentation and report.
• Several teams did not have a good schedule. If you
are one of these teams, please create a schedule and
include it with your progress report on Friday this
week.
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Administration
Next and final presentations
Sign up now
Team members who were unable to come to the first
presentation should attend the second
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Administration
Tests
There are 4 tests, each with 2 questions. The final grade will
be based on the best 6 questions out of 8.
Uncollected answer books are at 301 College Avenue.
Average grades:
Test 1 Q1
Test 1 Q2
Test 2 Q1
Test 2 Q2
7.7
6.3
6.1
7.9
Last time that this course was taught, poor test results were a
common reason for getting a poor overall grade for the course
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Test 2 Questions 1 (a)
Theater Ticket System allows a purchaser to buy theater tickets
online. In Phase 1, a purchaser will be able to either: (a) buy
tickets online, or (b) change or cancel a previous order.
To buy tickets online, the purchaser searches a database of
events to discover which tickets are available, chooses tickets,
adds them to a shopping cart, and possibly continues buying
more tickets for other performances.
When all items have been chosen, the purchaser provides
information to pay for the tickets by credit card. The
purchaser can choose to have the tickets sent by mail, or
arrange to collect them at the theater on the day of the
performance.
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Test 2 Questions 1 (a)
Draw a use case diagram that models the various ways in
which a purchaser interacts with this system. The diagram
should show a relationship to a use case, PaybyCredit, which
models credit card payments.
Definition from Lecture 9:
A use case is a a task that an actor needs to perform with the
help of the system.
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Test 2 Questions 1 (a)
Example from Lecture 9:
TakeExam
<<includes>>
Authenticate
ExamTaker
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CheckGrades
<<includes>>
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Test 2 Questions 1 (a)
Example from
Wikipedia:
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Test 2 Questions 1 (a)
FAQ about Use
Cases
See:
http://www.andrew.c
mu.edu/course/90754/umlucdfaq.html
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Test 2 Questions 1 (a)
Simple Solution
BuyTickets
<<includes>>
Purchaser
<<includes>>
These could
be combined
Change
PaybyCredit
<<includes>>
Cancel
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Test 2 Questions 1 (a)
More Complex Solution
<<extends>>
BuyTickets
Purchaser
SelectTickets
<<extends>>
AddtoCart
<<includes>>
PaybyCredit
<<includes>>
ChangeCancel
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Test 2 Questions 1 (a)
Incorrect Solution
BuyTickets
SelectTickets
<<includes>>
AddtoCart
Purchaser
PaybyCredit
<<includes>>
ChangeCancel
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System Design:
Data Intensive Systems
Examples
• Electricity utility customer billing (e.g., NYSEG)
• Telephone call recording and billing (e.g., Verizon)
• Car rental reservations (e.g., Hertz)
• Stock market brokerage (e.g., Charles Schwab)
• E-commerce (e.g., Amazon.com)
• University grade registration (e.g., Cornell)
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Architectural Style: Master File Update
Example: Electricity Utility Billing
Requirements analysis has identified several
transaction types:
• Create account / close account
• Meter reading
• Payment received
• Other credits / debits
• Check cleared / check bounced
• Account query
• Correction of error
• etc., etc., etc.,
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Electricity Utility Billing
First attempt:
Transaction
Data input
Master file
Bill
Each transaction is handled as it arrives.
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Criticisms of First Attempt
Where is this first attempt weak?
• All activities are triggered by a transaction
• A bill is sent out for each transaction, even if there are
several per day
• Bills are not sent out on a monthly cycle
• Awkward to answer customer queries
• No process for error checking and correction
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Electricity Utility Billing
Batch Processing: Edit and Validation
errors
Batches of
incoming
transactions
Edit &
validation
Data input
Batches of
validated
transactions
read only
Master file
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UML Deployment Diagram:
Validation
DataInput
EditCheck
RawData
ValidData
MasterFile
Check
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Electricity Utility Billing
Batch Processing: Master File Update
errors
Reports
Validated
transactions
in batches
Sort by
account
Batches of
input data
Master file
update
Bills
Checkpoints
and audit trail
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Electricity Utility Billing
Benefits of Batch Updating
• All transactions for an account are processed together
at appropriate intervals
• Backup and recovery have fixed checkpoints
• Better management control of operations
• Efficient use of staff and hardware
• Error detection and correction is simplified
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Architectural Style: Master File Update (basic)
Example: billing system for electric utility
Data input and
validation
Sort
Master file
update
Mailing and
reports
Advantages:
Efficient way to process batches of transactions.
Disadvantages:
Information in master file is not updated immediately.
No good way to answer customer inquiries.
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Online Inquiry: Use Case
AnswerCustomer
<<uses>>
CustomerRep
NewTransaction
A customer calls the utility and speaks to a customer
service representative. The representative can read the
master file, but not make changes to it.
If the representative wishes to change information in the
master file, a new transaction is created as input to the
master file update system.
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Online Inquiry
Customer
Service
Representative
read only
New
transaction
Master file
Customer Service department can read the master file, make
annotations, and create transactions, but cannot change the
master file.
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Architectural Style: Master File Update (full)
Example: billing system for electric utility
Data input and
validation
Sort
Master file
update
Mailing and
reports
Customer
services
Advantages: Efficient way to answer customer inquiries.
Disadvantages: Information in master file is not updated
immediately.
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Data Intensive Systems with
Real Time Transactions
Example: A Small-town Stockbroker
• Transactions
Received by mail or over telephone
For immediate or later action
• Complex customer inquiries
• Highly competitive market
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Real-time Transactions & Batch Processing
Real-time
transactions
This is a combination of the
Repository style and the
Master File Update style
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Data
input
Customer &
account database
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Extending the Repository Architectural Style:
A Small-town Stockbroker
Databases
• Customer and account database
• Financial products (e.g., account types, pension plans,
savings schemes)
• Links to external databases (e.g., stock markets, mutual
funds, insurance companies)
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Real-time Transactions
Real-time
transactions
Products &
services database
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Customer &
account database
External
services
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Real-time Transactions & Batch Processing
Real-time
transactions
Products &
services database
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Data
input
Batch
processing
Customer &
account database
External
services
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Stock Broker: Interface Diagram
OnLineTR
BatchTR
External
ProductDB
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CustomerDB
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Practical considerations to include in
Architecture and Specification
• Can real-time service during scheduled hours be
combined with batch processing overnight?
• How will the system guarantee database consistency
after any type of failure?
reload from checkpoint + log
detailed audit trail
• How will transaction errors be avoided and identified?
• How will transaction errors be corrected?
• How will staff dishonesty be controlled?
These practical considerations may be major factors in
the choice of architecture.
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Systems Architecture for Network Systems:
Firewall
Public
network
Private
network
Firewall
A firewall is a computer at the junction of two network
segments that:
• Inspects every packet that attempts to cross the boundary
• Rejects any packet that does not satisfy certain criteria, e.g.,
an incoming request to open a TCP connection
an unknown packet type
Firewalls provide security at a loss of flexibility and a cost of
system administration.
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Time-Critical Systems
A time-critical (real time) system is a software system
whose correct functioning depends upon the results
produced and the time at which they are produced.
• A soft real time system is degraded if the results
are not produced within required time constraints
e.g., a router is permitted to time out or lose a packet
• A hard real time system fails if the results are
not produced within required time constraints
e.g., a fly-by-wire control system for an airplane, must
respond within specified time limits.
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Time Critical System:
Architectural Style - Daemon
A daemon is used when messages sometimes arrive at closer
intervals than the the time to process them.
Daemon
Spawned
process
Example: Web server
The daemon listens at port 80
When a message arrives it:
spawns a processes to handle the message
returns to listening at port 80
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Software Considerations
In some types of system architecture, non-functional
requirements of the system may dictate the software
design and development process.
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Software Considerations:
Time-Critical System
Developers of advanced time-critical software
spend almost all their effort developing the
software environment:
• Monitoring and testing -- debuggers
• Crash restart -- component and system-wide
• Downloading and updating
• Hardware troubleshooting and reconfiguration
etc., etc., etc.
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Software Considerations:
Testing
Example: Testing multi-threaded and parallel systems
Several similar threads operating concurrently:
•
•
Re-entrant code -- separation of pure code from
data for each thread
May be real-time (e.g., telephone switch) or non-time
critical
The difficult of testing real-time, multi-threaded systems
may determine the entire software architecture.
•
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Division into components, each with its own
acceptance test.
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Software Considerations:
Continuous Operation
Many systems must operate continuously
•
Software update while operating
•
Hardware monitoring and repair
•
Alternative power supplies, networks, etc.
•
Remote operation
These functions must be designed into the fundamental
architecture.
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