Interface Analysis

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Business Requirements AnalysisITEC-455 Spring
2010

• Interface Analysis
• Professor J. Alberto Espinosa

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Objectives

• Discuss basic issues about interface analysis

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Interface
The place at which independent and often
unrelated systems meet and act on or communicate
with each other Webster dictionary
Network
Hardware
User
System
Software
Software
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Use Case Diagram without Interfaces
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Use Case Diagram with InterfacesEx.1 1
Interface per each Actor-UC Interaction
UML Symbolfor Interface
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Use Case Diagram with InterfacesEx.2 1
Interface for 1 Actors Interaction with all UCs
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Use Case Diagram with InterfacesEx.3 1
Interface for any Actor Interaction with 1 UC
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• If the actor is a user
• The interface specification describes how the
  user interacts with the system i.e., the user
  interface (UI) the human-computer
  interaction (HCI)
• If the actor is an external system
• The interface specification describes how the
  system interacts with that external system actor
  i.e., the application program interface (API)

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First Step Identify All InterfacesUser
Interfaces (UI) and System or Application
Program Interfaces (API)
UI
UI
UI
UI
UI
API
UI
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Next List all Interfaces
Interface Name Actor Type
Funds Withdrawal User UI
Funds Deposit User UI
Account Management User UI
Customer Activity Inquiry User UI
ATM Status Monitor User UI
Cash Replenishment User UI
Customer Accounts System System API
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Each Interface Needs to Have

• A name (e.g., Customer Interface)
• A type (e.g., UI, API)
• A set of operation signatures (for UI and API)
  indicating
• which data to get from the actor with the
  operation (i.e., Get UserId, Name, etc.)
• Which data to return to the actor when the
  operation is complete
• A storyboard (for UI only) visual illustration
  of the sequence of screen designs to complete
  these operations

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Example of Operation Signatures Funds
Withdrawal Interface

• Get data from card magnetic tapeGet pass code
  from customer
• Get customer transaction selection(user selects
  withdrawal)
• Get account type for withdrawal
• Get amount to withdraw
• Return cash and confirmation message
• Return new balance after withdrawal, or
• Return error message to customer
• Return thank you message to customer

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A User Interface Involves

• Inputs (Get) into the system by the user, e.g.
• Data entry into the system
• Query information from the system
• Voice command or input , etc.
• Outputs (Return) from the system to the user,
  e.g.
• A result display
• A printed output
• Voice or sound output

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Diagramming the Interface with Storyboards

• User interfaces can be diagrammed as
  storyboards
• A storyboard is a series of drawings that depict
  how the system looks at the start of the
  operation and after each significant change to
  the look of the interface
• Is like a sequence of screenshots that follows
  the use case execution sequence

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Organization of a Storyboard
Storyboard Sequence
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A Bad Interface Storyboard
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Ergonomics

• Ergonomics (or human factors) is the scientific
  discipline concerned with the understanding of
  the interactions among humans and other elements
  of a system
• Disciplines physical, cognitive and
  organizational ergonomics
• International Ergonomics Association

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Usability

• Derives from the industrial engineering field of
  Ergonomics how to design things so they are
  easy to use.It refers to the quality of a
  user's experience when interacting with a product
  or system and how well users can learn and use
  a product to achieve their goals and how
  satisfied they are with that process ... people
  who use the product can do so quickly and easily
  to accomplish their tasks usability.gov
• Other references http//www.usernomics.com/usabil
  ity.html

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User Interface Design

• Also referred to as Human Computer Interaction
  (HCI) is what the usability specialists do to
  build systems that are easy to use.
• HCI also derives from the field of Ergonomics,
  which is now being called Human Factors which
  incorporate cognitive ergonomics and interaction
  with digital/virtual systems (not just physical).
• Other references
• Cornell http//ergo.human.cornell.edu/ahtutorials
  /interface.htmlVirginia Tech http//www.edtech.v
  t.edu/edtech/id/interface/Carnegie Mellon
  http//www.usernomics.com/user-interface-design.ht
  ml

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Application Program Interface (API)

• Is a specification that describes how other
  systems or applications can interact with a
  system
• For example, if you wish to develop Windows or
  iPhone applications, you need to learn the
  Windows or iPhone API
• In a use case model an external system actors
  interaction with our system requires an API
• If our system will interact with an external
  system (arrow pointing out), we need to know the
  external systems API
• If the external system will interact with our
  system (arrow pointing in), the external system
  programmers need to know our systems API
• Google Earth API
• Google Maps API

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In Sum What to Include in an Interface Analysis
Specification

• A list of all the interfaces between actors and
  use cases
• For each interface (any actor user or external
  system)
• Indicate whether the actor is a user (human
  actor) or an external system
• Prepare a list of operation signatures detailing
  all the data that is passed to/from the system
  before each operation and the data that is
  returned from/to the system after each operation
• For users (human actors only)
• Indicate when/if operations are taking place for
  data input, display outputs or printed outputs
• Prepare a storyboard for all screen input/output
  displays and printouts
• Analysis of the visual UI for all screen
  input/output displays and printouts
• For external system actors (only)
• Indicate when/if operations are taking place to
  input or output data from/to the system
• Analysis of the system API

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General Quality Attributes of a User Interface
Design

• Ease of use
• Intuitive use and navigation
• Consistency across screens
• Simplicity e.g., no clutter, no information
  overload, no busy graphics
• Exit/cancel options for users
• Forgiving
• Businesslike appearance
• Readable and good color contrast