Lecture 19 Chapter 9 (to the end) Chapter 11 (start) (Note

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Lecture 19Chapter 9 (to the end)Chapter 11
(start)(Note we will not be covering chapter
10 Designing Databases)
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Inheritance, Overriding and Polymorphism

• Strength of OO development
• Built-in capabilities that facilitate programming
  and maintenance
• Class inheritance represents generalization and
  specialization
• Specialization classes inherit the attributes and
  relationships of the parent class
• When naming a class, including the name of the
  parent class indicates that a class is a
  specialization class that will inherit both the
  attributes and the methods of the parent class
• Syntax is to name class with
• Class Name Parent Class
• Example class Savings Account inherits from
  Account
• Savings Account Account

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Account
Account number Balance Date opened
Make deposit Make withdrawal
Savings AccountAccount
Checking AccountAccount
Check style Minimum balance
Interest rate
Calculate interest
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Inheritance (continued)

• The notation Checking Account Account
  indicates that checking account is a
  specialization of account
• This means a checking account inherits attributes
  such as Name and Address and methods like
  MakeDeposit and MakeWithdrawal
• This inheritance happens automatically
• Good to use inheritance when you can

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Overriding inheritance

• Override to enable a method in a sub-class to
  replace the logic from the method in the parent
  class
• e.g. suppose the application requires that a
  savings account be opened with a minimum deposit
  of 100
• So the CreateAccount method for a savings account
  would be a little different than for other kinds
  of accounts
• By defining the method in the subclass, you
  override the method as it is described in the
  superclass see next slide the definition of
  Make deposit in the subclass overrides the one in
  the superclass

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Account
Account number Balance Date opened
Make deposit Make withdrawal
Savings AccountAccount
Checking AccountAccount
Check style Minimum balance
Interest rate
Make deposit Calculate interest
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Polymorphism

• Polymorphism the reuse of methods for different
  classes that are distinct even though they may
  have the same name and parameter list
• E.g. if we define a method in the Customer class
  called GetBalance, we can also define a method in
  the Account class also called GetBalance, and the
  two would do different things (e.g. the one in
  Customer returns the sum of all savings and
  checking accounts, while in the Account class it
  would only return a balance for that single
  account

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Integrating the Object-oriented application
design with user interface design,database
design and network design

• We have focused mostly on application design
  above
• Regarding the user interface
• Since the OO design results in a set of
  independent interacting classes the overall
  structure of the system will not change due to
  the user interface
• A set of interface classes are designed and added
  to the overall class diagram
• There are many already built tools and libraries
  of components that can be used with OO interface
  design
• Can involve selecting a library of tools,
  designing reports and forms and inserting logic
  within the methods to access them
• Design of the application classes is best done in
  conjunction with the design of the user interface

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• Regarding the database
• Database access is usually provided through a set
  of database classes
• Some OO languages can automatically read and
  write to the database, while others require
  specific calls to database interface objects
• Identifying the target language and database
  system is important in order that appropriate
  integration can be done during design
• Regarding networks
• Object-oriented applications frequently execute
  in a distributed environment
• Individual objects (or classes) can be assigned
  to separate nodes
• However, appropriate middleware will be necessary
  to ensure there is no conflicts between objects

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Need for Project Coordination

• Coordinating all the activities during design can
  be difficult
• Many business rules may have to be incorporated
  in the system
• Management may still be making decisions while
  the project is being developed
• Projects begin to fragment based on number of
  design issues to be addressed

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• The system may need to be subdivided into
  subsystems
• Each subsystem may have its own unique design
  requirements
• The project team may be divided into smaller
  teams to focus on the various subsystem
• Some technical issues (e.g. network
  configuration, database design etc.) may be
  common to all subsystems
• Others (e.g. response time etc.) may be limited
  to specific subsystems
• All of these teams will need to be coordinated

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• Two mini projects may be initiated at this point
• Data conversion project
• Test case development project
• Activities of implementation phase, such as
  programming, begin around this time
• Often design and programming may be conducted
  concurrently
• Other complications
• In addition to groups working on design issues,
  groups of programmers may also be getting added
  to the team
• Also people may be working at different locations
• Communication becomes exponentially more
  complicated as more people get added!
• Project management tools and techniques are needed

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Coordinating Project Teams

• Fundamental tool in coordinating activities of
  the project team is the project schedule
• The project manager must update the project
  schedule as time goes by
• During the analysis phase project management is
  often done by the project manager and an
  assistant.
• Once the project expands and several teams are
  formed a committee may be formed of the leaders
  of the key design and implementation teams and
  may carry out more of the coordination and
  control
• Weekly and sometimes daily status meetings may be
  held

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Coordinating Information

• Development of design models generates a great
  amount of detail
• Modules, classes, data fields, data structures,
  forms, reports, methods, subroutine details are
  defined in detail
• Takes a lot of coordination to keep track of all
  the information
• Two kinds of tools help
• CASE tools (with a central repository to capture
  information)
• Central repository allows all teams to view
  project information (see next slide)

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• Other electronic tools to help with team
  communication and information coordination
• Computer support for collaborative work (CSCW)
• Allows for team members to work on and
  dynamically update working documents or diagrams
• One such system is Lotus Notes
• A difficult part of the development project is to
  keep track of open items and unresolved issues
• Can have an open items control log
• A sequential list of all open items with
  information to track responsibilities and
  resolution of the open items (see Appendix A)

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Chapter 11- Designing Inputs, Outputs, and
Controls

• Major issue in the design of systems
• How to provide access to required information
  while at the same time protecting the information
  from damage (both accidental or intentional)
• Integrity controls
• Mechanisms and procedures that are built into the
  system to safeguard both the system and the
  information contained in the system
• E.g. how do we ensure that only a manager sees
  sensitive pay information?
• E.g. How does a company using a LAN protect its
  sensitive data from outsiders?

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Objectives of Integrity Controls

• Ensure that only appropriate and correct business
  transactions occur
• Focuses on identification and capture of input
  transactions to ensure that all important
  transactions are included and fraudulent ones are
  not entered
• Ensure that the transactions are recorded and
  processed correctly
• Controls used to alert users to data-entry errors
  and system bugs
• Protect and safeguard the assets of the
  organization
• Protect from crashes, catastrophes and hackers
  etc.

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System Access Controls

• System access controls mechanisms that restrict
  or control what portions of the computer system a
  person can use
• Includes controls to limit access to certain
  applications or functions, the computer itself or
  pieces of data
• Most systems build on the access control already
  within system software
• Categories of users
• Unauthorized user a person who does not have
  authorized access to a system
• E.g. former employees and oustiders like hackers
  and intruders
• Registered user a user who is registered or
  known to the system and is authorized to access
  some part of it
• Different levels of access are defined for
  different users
• Privileged user a user who has special security
  access privileges to a system
• E.g. system programmers, application programmers,
  operators etc.

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• Physically securing locations
• Physically secure locations protect physical
  equipment such as computers, hard disk storage
  devices and backup data tapes
• Some mainframe computers require supervisory
  functions be done at a specific console
• Managing User Access
• Most common methods
• A user identifier (ID) and password
• Two techniques to define passwords
• Computer can randomly generate and assign
  passwords
• Each user can define his or her own password
• Security system should be organized so all
  resources can be accessed using the same unique
  identifier and password (so dont have to know
  many of these within one organization)
• Some companies require password changes every 30
  days
• Systems keep record of attempted (unsuccessful)
  logins

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• Controlling Access with Visibility
• An important type of control determines what each
  user actually sees and must be integrated into
  the application system itself
• Designers define and develop the various levels
  of visibility and access
• Defined by
• The various classes of registered users
• Which functions, screens, forms, fields, reports
  etc. will be available to those classes of users
• E.g. a salesperson may be able to see their own
  orders, sales and commisions
• A supervisor may be able to view the performance
  of salespeople in his area etc.
• Level of visibility increases with level of
  authority and responsibility in an organization

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Input Integrity Controls

• Input integrity controls are used with all
  mechanisms
• From specific electronic devices to standard
  keyboard inputs
• Input controls are an additional level of
  verification that helps reduce errors on input
  data an input device cannot ensure that all the
  necessary fields have been entered so need this
  additional level of verification or control
• Historically the most common method to ensure
  correct input was to enter data twice (keypunch
  verify)
• Other methods are used today (see next slide)

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Common techniques used to verify input

• Field combination controls
• Review various combinations of fields to ensure
  that the correct data is entered. Eg. On an
  insurance policy the application data must be
  prior to the policy date
• Value limit controls
• Check numeric fields to make sure that the amount
  entered is reasonable. E.g. the amount of a sale
  or the amount of a commission should fall within
  a range
• Completeness controls
• An integrity control to ensure that all necessary
  fields on an input form have been entered (e.g.
  if a dependent is entered on a form, then that
  persons birthday must also be entered)

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• Data validation controls
• Ensure that numeric fields that contain codes are
  correct
• E.g. bank account numbers might be created with a
  7 digit field and a trailing check digit to make
  an 8 digit account number
• The check digit is based on the previous seven
  digits, and the system recalculates it (using
  data entered) as the the data-entry person enters
  the account number with check digit
• If the results dont match an error has occurred