Usability
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Usability Usability Presentation Transcript

  • Software Engineering Usability 1 CS 5150 1
  • The Importance of User Interface Design A computer system is only as good as the interface it provides to its users • Elegant design, appropriate functionality, & responsive system: => a measurable difference to their effectiveness • A system that is hard to use: => users may fail to find important results, or mis-interpret what they do find => user may give up in disgust Good support for users is more than a cosmetic flourish CS 5150 2
  • Usability: The Analyze/Design/Build/Evaluate Loop Design Analyze requirements User testing ? Build Evaluate The Information Science and Communication departments offer a series of courses in Human Computer Interaction. CS 5150 3
  • Processes for User Interfaces It is almost impossible to specify an interactive interface in a textual document • Requirement specifications benefit from sketches, comparison with existing systems, etc. • Design specifications should definitely include graphical elements and benefit from a mock-up or other form of prototype. • Schedules should include user testing and time to make changes. User interfaces must be tested with users. Expect to change the requirements as the result of testing. CS 5150 4
  • Tools for Usability Requirements and Evaluation Initial Client's opinions √ Competitive analysis √ Expert opinion Focus groups Mock-up Prototype Production Observing users Measurements CS 5150 √ √ √ √ √ √ √ √ √ √ √ √ 5
  • Tools for Usability Requirements: Mock-up CS 5150 6
  • Tools for Usability Requirements: Focus Group A focus group is a group interview • Interviewer • Potential users Typically 5 to 12 Similar characteristics (e.g., same viewpoint) • Structured set of questions May show mock-ups Group discussions • Repeated with contrasting user groups CS 5150 7
  • Usability: Accessibility Requirements Requirements about accessibility (e.g., support for users with disabilities) are most likely to arise in the user interface. You may have a legal requirement to support people with disabilities. Example of requirements specification: The system must comply with Section 508 of the US Rehabilitation Act. See http://www.section508.gov/ CS 5150 8
  • Design from a System Viewpoint Usability is more than interface design interface design mental model interface functions data and metadata computer systems and networks CS 5150 9
  • Examples of Mental Model The mental model is the user's internal model of what the system provides: • The desk top metaphor -- files and folders • The web search model -- one vast collection of pages, which are searched on request Also called conceptual model CS 5150 10
  • Mental Model A mental model is what a user thinks is true about a system, not necessarily what is actually true • Model should be similar in structure to the system that is represented • Model allows a person to predict the results of his actions • Model is simpler than the represented system. A mental model includes only enough information to allow accurate predictions (e.g., no data structures) CS 5150 11
  • Interface Design The interface design is the appearance on the screen and the actual manipulation by the user • Fonts, colors, logos, key board controls, menus, buttons • Mouse control or keyboard control • Conventions (e.g., "back", "help") Examples: • Screen space utilization in Adobe Reader. • Number of snippets per page in Web search. CS 5150 12
  • Principles of Interface Design Interface design is partly an art, but there are general principles: • Consistency -- in appearance, controls, and function. • Feedback -- what is the computer system doing? why does the user see certain results? • Users should be able to interrupt or reverse actions • Error handling should be simple and easy to comprehend • Skilled users should be offered shortcuts; beginners should have simple, well-defined options The user should feel in control CS 5150 13
  • Interface Functions The interface functions determine the actions that are available to the user: • Select part of an object • Search a list or sort the results • View help information • Manipulate objects on a screen • Pan or zoom There may be alternative user interface designs for the same interface functions, e.g., Macintosh v. Windows desktop have most of the same interface functions, but different designs. CS 5150 14
  • Data and Metadata Data and metadata stored by the computer system enable the interface functions and the interface design. • Effectiveness of searching depends on the type and quality of data that is indexed (free-text, controlled vocabulary, etc.) • The desktop metaphor has the concept of associating a file with an application. This requires a file type to be stored with each file: -- extension to filename (Windows and Unix) -- resource fork (Macintosh) Inexperienced clients sometimes ask for interface functions that require additional data or metadata. CS 5150 15
  • Computer Systems and Networks The performance, reliability and predictability of computer systems and networks is crucial to usability Examples • Instantaneous response time for mouse tracking and echo of key stroke • Pipelined algorithm for a page turner • Quality of service for real time information, e.g., audio CS 5150 16
  • Computer Systems and Networks: Requirements Performance, Reliability, Scalability, Security… Example: Response time 0.1 sec – the user feels that the system is reacting instantaneously 1 sec – the user will notice the delay, but his/her flow of thought stays uninterrupted 10 sec – the limit for keeping the user's attention focused on the dialogue CS 5150 17
  • Computer Systems and Networks: Device-Aware Interfaces Interfaces must take into account physical constraints of computers and networks: • How does a desk-top computer differ from a laptop? • What is special about a smart phone? • How do you make use of a touch-sensitive screen? • What works well with a digital camera? Constraints that the interfaces must allow for: => performance of device (e.g., fast or slow graphics) => limited form factor (e.g., small display, keyboard) => connectivity (e.g., intermittent) CS 5150 18
  • Interface Design: Command Line Interfaces User interacts with computer by typing commands (e.g., Linux shell script) • Allows complex instructions to be given to computer • Facilitates formal methods of specification & implementation • Skilled users can input commands quickly • Unless very simple, requires learning or training • Can be adapted for people with disabilities • Can be multi-lingual • Suitable for scripting / non-human clients CS 5150 19
  • Interface Design: Command Line Interfaces SEARCH I NSPEC Da t a b a s e --------------------------------------Ty p e k e y wo r d s a n d p r e s s RETURN - - o r e n t e r a c o mma n d De f a u l t i s ADJ : a c i d f r e e --------------------------------------Se t # 3 : 0 r e c or ds a c i d a dj f r e I NSPEC Da t a b a s e Se t # 4 : 5 r e c or ds a c i d a dj f r e e I NSPEC Da t a b a s e Se t # 5 : 448 r e c or ds a c i d a nd pa pe r I NSPEC Da t a b a s e Se t # 6 : de a c i di f i c a t i on 4 r e c or ds I NSPEC Da t a b a s e --------------------------------------- CS 5150 20
  • Command Line Interfaces and Text-only Menus Command line interfaces and text-only menus had become largely replaced by graphical interfaces, but are returning: • Devices with small form factor or other special features, e.g. cell phone, PDA, etc. • Interfaces for simple tasks with general users, e.g. automated bank teller (ATM) CS 5150 21