CS 5150 1

CS 5150 Software Engineering

Lecture 14

System Architecture 2

CS 5150 2

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.

CS 5150 3

Administration

Next and final presentations

Sign up now

Team members who were unable to come to the first presentation should attend the second

CS 5150 4

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

CS 5150 5

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.

CS 5150 6

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.

CS 5150 7

Test 2 Questions 1 (a)

Authenticate

TakeExam

<<includes>>

<<includes>>

CheckGradesExamTaker

Example from Lecture 9:

CS 5150 8

Test 2 Questions 1 (a)

Example from Wikipedia:

CS 5150 9

Test 2 Questions 1 (a)

FAQ about Use Cases

See: http://www.andrew.cmu.edu/course/90-754/umlucdfaq.html

CS 5150 10

Test 2 Questions 1 (a)

Simple Solution

BuyTickets

PurchaserPaybyCredit

<<includes>>

Change <<includes>>

Cancel

<<includes>>

These could be combined

CS 5150 11

Test 2 Questions 1 (a)

More Complex Solution

BuyTickets

PurchaserPaybyCredit

<<includes>>

ChangeCancel

<<includes>>

SelectTickets

AddtoCart

<<extends>>

<<extends>>

CS 5150 12

Test 2 Questions 1 (a)

Incorrect SolutionBuyTickets

PurchaserPaybyCredit

<<includes>>

ChangeCancel

<<includes>>

SelectTickets

AddtoCart

CS 5150 13

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)

CS 5150 14

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.,

Architectural Style: Master File Update

CS 5150 15

Electricity Utility Billing

First attempt:

Data input Master fileTransaction Bill

Each transaction is handled as it arrives.

CS 5150 16

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

CS 5150 17

Electricity Utility BillingBatch Processing: Edit and Validation

Data input

Master file

Edit & validation

read only

errors

Batches of validated transactions

Batches of incoming transactions

CS 5150 18

UML Deployment Diagram:Validation

MasterFile Check

EditCheck

ValidData

DataInput

RawData

CS 5150 19

Electricity Utility BillingBatch Processing: Master File Update

Master fileupdate Bills

Validated transactionsin batches

Sort by account

errors

Reports

Batches of input data

Checkpoints and audit trail

CS 5150 20

Electricity Utility BillingBenefits 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

CS 5150 21

Architectural Style: Master File Update (basic)

Master file update

Data input and validation

Mailing and reports

Example: billing system for electric utility

Advantages:

Efficient way to process batches of transactions.

Disadvantages:

Information in master file is not updated immediately.No good way to answer customer inquiries.

Sort

CS 5150 22

Online Inquiry: Use Case

CustomerRep

AnswerCustomer

NewTransaction

<<uses>>

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.

CS 5150 23

Online Inquiry

Master file

read only

Customer Service Representative

Customer Service department can read the master file, make annotations, and create transactions, but cannot change the master file.

New transaction

CS 5150 24

Architectural Style: Master File Update (full)

Example: billing system for electric utility

Advantages: Efficient way to answer customer inquiries.

Disadvantages: Information in master file is not updated immediately.

Customer services

Master file update

Data input and validation

Mailing and reports

Sort

CS 5150 25

Data Intensive Systems with Real Time Transactions

• Transactions

Received by mail or over telephone

For immediate or later action

• Complex customer inquiries

• Highly competitive market

Example: A Small-town Stockbroker

CS 5150 26

Real-time Transactions & Batch Processing

Customer & account database

Real-time transactions

Data input

This is a combination of the Repository style and the Master File Update style

CS 5150 27

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)

CS 5150 28

Real-time Transactions

Customer & account database

Products & services database

Real-time transactions

External services

CS 5150 29

Real-time Transactions & Batch Processing

Customer & account database

Products & services database

Real-time transactions

Batch processing

Data input

External services

CS 5150 30

Stock Broker: Interface Diagram

CustomerDBProductDB

OnLineTR BatchTR

External

CS 5150 31

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 + logdetailed 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.

CS 5150 32

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 connectionan unknown packet type

Firewalls provide security at a loss of flexibility and a cost of system administration.

CS 5150 33

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.

CS 5150 34

Time Critical System: Architectural Style - Daemon

Daemon

Example: Web server

The daemon listens at port 80

When a message arrives it:spawns a processes to handle the messagereturns to listening at port 80

Spawned process

A daemon is used when messages sometimes arrive at closer intervals than the the time to process them.

CS 5150 35

Software Considerations

In some types of system architecture, non-functional requirements of the system may dictate the software design and development process.

CS 5150 36

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.

CS 5150 37

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.

• Division into components, each with its own acceptance test.

CS 5150 38

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.