Transcript COSC3311 – Software Design Section P Vassilios Tzerpos

COSC3311 – Software Design
Section P
Vassilios Tzerpos
Department of Computer Science, York University
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2016-05-27 8:39 AM
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Course Details
 www.cs.yorku.ca/course/3311
 Slides and other resources:
http://www.cs.yorku.ca/course/3311/sectionP/
 Case studies:
http://www.cs.yorku.ca/course/3311/sectionM/
 Eiffel Help:
www.cs.yorku.ca/eiffel
 Office hours: WF 2:30 – 3:30
 Read newsgroup
 Lab hours next week:
 Monday, January 12
3-4
 Wednesday, January 14 3-4
 Friday, January 16
3-4
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Grading
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Assignment 1: 7%
Assignment 2: 10%
Assignment 3: 13%
Test: 25%
Exam: 45%
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Textbook
 Bertrand Meyer: Object-Oriented Software
Construction, 2nd edition. Prentice Hall, 1997.
 Suggested reading:
 Pete Thomas, Ray Weedon, Object-Oriented Programming
in Eiffel, second edition, Addison-Wesley, 1998.
 Kent Beck, Test-driven development : by example.
Addison-Wesley, Boston, 2003.
 J.M. Jezequel and C. Mingins. Design patterns and
contracts. Addison-Wesley, 2000.
 Erich Gamma et al.: Design Patterns. Addison-Wesley,
1995.
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Advice – Course strategy
 Don’t fall behind: First two weeks especially!
 Attend lectures: material is not all in textbook
 Do the readings on time
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Week 1 – Readings
 January 5
 Software Quality & Engineering -- The context for design;
what is design; Eiffel programming; classes.
 Readings Required: Chapter 7
 Static Structure
 Classes
 Class POINT …
 Readings Background: Chapters 1, 2
 External Quality
 Internal Quality – Modularity
 Read about, install and use EiffelStudio
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The goal: Software quality
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REUSABILITY
EXTENDIBILITY
RELIABILITY (Correctness + Robustness)
PORTABILITY
EFFICIENCY
SPECIFICATION
…
Robustness
 Correctness:
 The ability of a software system to perform according to
specification, in cases defined by the specification.
 Robustness:
 The ability of a software system to react in a reasonable
manner to cases not covered by the specification.
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Case Study 1– Bank example
 Requirements & Use Cases  Design Constructs
BON
 Design – How?
Contracts
Object equality: equal
Genericity
Agents and Tuples
Design Patterns (Singleton)
Plan-driven: Identify the
Classes
Agile: Test Driven
Development
 EiffelStudio
Clusters and Classes
Tests and ETester
Project Configuration/Ace files
Debugger
Documentation
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Requirements – Bank example
 Requirements
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Open an account for a customer (savings or chequing)
Deposit
Withdraw
Display details of an account
Change LOC
Produce monthly statements
Print a list of customers
…
 Ambiguities
 What is the difference between savings and chequing?
 Many others …
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Case Study 1 – Bank example
 How should we go from Requirements to Code?
 Two basic approaches
 Plan-driven (waterfall type models)
 Agile (incremental approaches)
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Requirements to Code?
How to bridge
the gap between
requirements
and code?
???
Code
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The waterfall model of the lifecycle
FEASIBILITY STUDY
REQUIREMENTS
ANALYSIS
SPECIFICATION
GLOBAL DESIGN
DETAILED DESIGN
IMPLEMENTATION
VALIDATION &
VERIFICATION
DISTRIBUTION
PROJECT PROGRESS
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Problems with the waterfall
 Late appearance of actual code.
 Lack of support for requirements change — and
more generally for extendibility and reusability.
 Lack of support for the maintenance activity (70%
of software costs?).
 Division of labor hampering Total Quality
Management.
 Impedance mismatches.
 Highly synchronous model.
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Impedance mismatches
As Management requested it.
As Programming developed it.
As the Project Leader defined it.
As Operations installed it.
As Systems designed it.
What the user wanted.
(Pre-1970 cartoon; origin unknown)
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How to think about requirements?
 Use Cases
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Bank Requirements – Use Cases
System
boundary
Actors
Use Case
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Bank Use Cases
 Challenge question:
 What would the Use Case diagram look like if the
bank supplies ATMs in addition to tellers?
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Use Case – Open Account
 Actors: Customer (initiator), Teller
 Overview: the customer applies for and is granted
a new bank account with some initial approved line
of credit. The teller logs on to the system, selects
open account , and supplies the new account
details. The system prints a copy of the contents
of the new account with the date, which the teller
hands to the customer.
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Design of Bank – Identify Classes
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TELLER
CUSTOMER
SAVINGS_ACCOUNT
CHEQUING_ACCOUNT
MAIN_MENU
BALANCE_INQUIRY
INTEREST_RATE ………
 Where do we start?
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Test Driven Development
1. Write a little Test
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Test will not work initially (there is no code)
Might not even compile
2. Make the Test work quickly
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Commit whatever sins are necessary in the process (e.g.
duplication in the code)
3. Refactor
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Eliminate the duplication created in merely getting the
test to work
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EiffelStudio – create a new project
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Call the new project bank
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Compile and Run
print(“hello world!”)
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Compile often!
 Always start with a compiled system
 New project wizard
 Copy an existing system
 A compiled system is needed for browsing
 Compile often!
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ETester – Create a tests cluster
Click here
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Create class ACCOUNT_TEST
Click here
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Clusters and Classes
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Ace file – Directory Structure
d0
d1
d2
d3
d4
Directory (cluster)
f1.e
f3.e
Class file
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Ace File – Ace.ace
http://www.cs.yorku.ca/eiffel/precompiled
system
"bank“
root
root_class: make
default
precompiled ("C:\Eiffel53\precomp\spec\windows\base")
assertion (check)
assertion (require) …
cluster
root_cluster:
"."
all tests:
".\tests"
library base:
exclude
"$ISE_EIFFEL\library\base"
end
end …
"table_eiffel3"; "desc";
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Project Configuration (Ace file)
Click here
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Root Class
All contracts
ACCOUNT_TEST
turned on
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Write Test
test_create_account: BOOLEAN is
local
c: CUSTOMER
do
comment("test_create_account")
create c.make("Archie Fox")
Result := equal(c.name, "Archie Fox")
end
Error code: VTCT
Error: type is based on unknown class.
What to do: use an identifier that is the name of a class in the
universe.
Class: ACCOUNT_TEST
Unknown class name: CUSTOMER
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The Test specifies a Design
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customer.e
indexing
description: "A bank customer“
class CUSTOMER create
set_name
feature -- Element change
make (a_name: STRING) is
-- Create a customer. Set `name' to `a_name'.
require
a_name_not_void: a_name /= Void
do
name := a_name
ensure
name_assigned: name = a_name
end
feature -- Access
name: STRING
-- of customer
invariant
name_not_void: name /= Void
end
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ETester GUI – Green bar
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Test: A customer with a savings account
test_create_customer_with_account: BOOLEAN is
local
a1,a2: SAVINGS_ACCOUNT
c: CUSTOMER
initial_deposit: REAL
do
initial_deposit := 500
create a1.make(initial_deposit)
check a1.balance = initial_deposit end
create c.make(a1, "Archie Fox")
a2 := c.account
Result := equal(c.name, "Archie Fox") and
a2 = a1 and a2.balance = initial_deposit
end
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Red bar
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Use debugger to find problem
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EiffelStudio – BON tool
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Client-Supplier relationship
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Open Account Use case (revisited)
 Actors: Customer (initiator), Teller
 Overview: the customer applies for and is granted
a new bank account with some initial approved line
of credit. The teller logs on to the system, selects
open account , and supplies the new account
details. The system prints a copy of the contents
of the new account with the date, which the teller
hands to the customer.
 We have not yet dealt with the LOC, system menu
and the receipt. We leave this as an exercise.
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Withdraw Use Case
 Actors: Customer (initiator) and Teller
 Overview: The customer provides the teller with
an account number and a withdrawal amount. The
teller selects `withdraw-request’ from the system
menu, and enters the data. The System debits the
account by the requested withdrawal amount, and
prints a receipt with the date and the amount,
which the teller gives to the customer.
 Question: What happens if there is not enough
money in the account to withdraw?
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test_withdraw
test_withdraw: BOOLEAN is
local
sa1, sa2: SAVINGS_ACCOUNT
initial_deposit: REAL
do
comment("test_withdraw")
initial_deposit := 500
create sa1.make(initial_deposit)
create sa2.make(200)
sa1.withdraw(300)
Result := equal(sa1, sa2)
end
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Bank design (BON static diagram)
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EiffelStudio feature tool – withdraw
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Run tests
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