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CS 5150 Software Engineering

Lecture 14

System Architecture 2

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Administration

Next and final presentations

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

Office hours

No office hours tomorrow, October 18.

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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

6.9 6.2 8.4 7.8

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 Question 2

The Pizza Ordering System allows the user of a web browser to order pizza for home delivery. To place an order, a shopper searches to find items to purchase, adds items one at a time to a shopping cart, and possibly searches again for more items.

When all items have been chosen, the shopper provides a delivery address. If not planning to pay with cash, the shopper also provides credit card information.

The system has an option for shoppers to register with the pizza shop. They can then save their name and address information, so that they do not have to enter this information every time that they place an order.

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Test 2 Question 2 (i)

Develop a use case diagram, for a use case for placing an order, PlaceOrder. The use case should show a relationship to two previously specified use cases, IdentifyCustomer, which allows a user to register and log in, and 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 Question 2 (i)

Authenticate

TakeExam

<<includes>>

<<includes>>

CheckGradesExamTaker

Example from Lecture 9:

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Test 2 Question 2 (i)

FAQ about Use Cases

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

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Test 2 Question 2 (i)

Example from Wikipedia:

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Test 2 Question 2 (i)

Shopper

PlaceOrder

<<includes>>

IdentifyCustomer

PaybyCredit

<<includes>>

Correct solution

Optional link

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Test 2 Question 2 (i)

Incorrect SolutionSearchMenu

PaybyCredit

<<includes>>

IdentifyCustomer

<<includes>>

AddtoCart

Pay

Shopper

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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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Example: Electricity Utility Billing

Requirements analysis identifies 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

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Electricity Utility Billing

First attempt:

Data input Master fileTransaction 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 BillingBatch Processing: Edit and Validation

Data input

Master file

Edit & validation

read only

errors

Batches of validated transactions

Batches of incoming transactions

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UML Deployment Diagram:Validation

MasterFile Check

EditCheck

ValidData

DataInput

RawData

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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

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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

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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

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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.

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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

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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

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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

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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

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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

Customer & account database

Products & services database

Real-time transactions

External services

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Real-time Transactions & Batch Processing

Customer & account database

Products & services database

Real-time transactions

Batch processing

Data input

External services

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Stock Broker: Interface Diagram

CustomerDBProductDB

OnLineTR BatchTR

External

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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 + 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.

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System Design: Non-Functional Requirements

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

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Non-functional requirements: 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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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 network 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

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 might arrive at closer intervals than the the time to process them.

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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.

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

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Software Considerations:Time-Critical System

Developers of advanced time-critical software spend much of 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.