Systems Analysis & Design: Topic 9b


User Interface Design


User Interface


Approach to Interface Design

  1. The tasks to be supported by the system are analyzed.
  2. Based on the physical data flow diagrams or use cases of the proposed system, the user interfaces required for the system are identified.
  3. Based on an understanding of the system's tasks and intended users, the design of each user interface is specified and aligned with the users' skill level and the logical flow of their tasks.
  4. Prototypes of the interfaces are often constructed and demonstrated to the users to gain their feedback.

Note: Because a good interface combines aesthetics, usability, and functionality, designing user interfaces is as much an art as it is a science.


Five-Step Process for Interface Design

(1) Analyze the Users and their Tasks Task analysis is used to identify, categorize, and define the procedures users employ to perform work tasks.
(2) Identify Required User Interfaces Examine physical DFDs to identify the documents, data entry screens, printed and screen reports, and other interfaces it requires.
  A user interface is required whenever a manual process interacts with an automated process or an external entity provides input to or receives output from a process.
(3 & 4) Select a Dialog Type and Develop a Prototype Design the command hierarchy, detailed interactions between user and system, and the interface objects required to manage the interactions.
(5) Review and Revise Prototype Validates the design but also builds user commitment because users feel that their needs and opinions were considered.
  Usability tests can help to ensure that system interfaces are easy to learn and use and that they support the desired level of user productivity.
  User reviews should be conducted repeatedly during the iterative analysis, design, and prototyping stage.

Supplemental Notes


Types of User Interfaces

Command Dialog A command dialog triggers the execution of system functions by employing a command language that defines the valid terms and syntax for execution.
  Although command dialogs are appropriate for compute-literate frequent users, they are inappropriate for most business users.
Menu Dialog A menu dialog lists several possible actions and requires the user to select an option.
  Menu dialogs are especially appropriate for infrequent or inexpert users.
Form-Filling Dialog A form-filling dialog typically replicates a source document and requires the user to fill in the form.
  This form of dialog is appropriate for novice or infrequent users.
Direct-Manipulation Dialog A direct manipulation dialog is one in which a pointing device such as a mouse is used to manipulate screen objects that perform system functions.
  Direct manipulation interfaces provide several benefits such as ease of learning and ease of use, and are therefore appropriate for novice users.
  examples: point-and-click menu selection; double-clicking icons to launch applications or to open files, using drag-and-drop to copy a file
  History of the Desktop User Interface.



User Documentation


CRITERIA FOR EVALUATING USER INTERFACE DESIGNS

Mental Model

Simplification of Tasks

Clarity

Consistency


Example Use Case

Use Case Name: Rental Customer Rents Rental Tape(s)
Use Case Purpose: Describes the process of renting rental tapes to rental customers
Uses: Rental Customer Pays Fines; Customer Makes Payment
Extended by: Rental Customer Rents 3/3 Rental Tapes
Typical Course of Events:
The main menu is displayed on the screen; waiting for employee number and menu selection:
  • When a customer presents membership card and selected rental tapes for check out, this use case is initiated by the sales clerk's entering a valid employee number and selecting "Process order" from the main menu. The Process Orders menu is displayed.
Waiting for menu selection:
  • The sales clerk selects "Process rental orders."
The rental order screen is displayed; waiting for member number:
  • The sales clerk scans the member number from the membership card, and the system verifies that the member number is valid and that the rental customer has no unpaid fines.
  • If the member number is valid, the system completes the rental order header, indicating a valid employee number, a valid member number, order number, and order date.
  • The system prompts the sales clerk to enter a rental tape stock number.
Waiting for stock number:
  • The sales clerk scans the stock number from the rental tape.
  • For each rental tape being rented, the system creates a rental order line, giving the stock number, title, rental category, and rental fee of each rental tape; in addition, the due date calculated for each rental tape is shown on the rental order line.
  • The system prompts the sales clerk to enter another rental tape stock number or to signal the end of the order.
  • If another stock number is entered, the system creates another rental order line.
Waiting for end of order indicator:
  • When the sales clerk signals the end of the order, the system creates a rental order footer by calculating and displaying the total cost for the order.
  • Customer makes payment. (See Customer Makes Payment use case.)
Waiting to print receipt:
  • The sales clerk requests that the receipt be printed.
  • The system prints the rental order receipt.
  • The customer signs the rental order receipt.
  • The customer is given one copy of the receipt; the other copy is retained for the audit file.

Figure: Partial detailed use case for Rental Customer Rents Rental Tape(s)
Adapted from: S.D. Dewitz, Systems Analysis and Design and the Transition to Objects, McGraw-Hill, 1996.