CS 5150 Software Engineering Lecture 9 Usability 1

CS Administrivia Surveys cancelled Not all team members need to attend every presentation Every team member must present at least once

CS A Couple of Interesting News Items US Patent and Trademark Office attempting to crowd-source patent review Dual licensing fiasco

CS The Usability Corollary to Schneier’s Law Any person can invent a security system so clever that he or she can’t imagine a way of breaking it Any person can design an interface so intuitive that he or she can’t imagine a way of misusing it

CS Software Must Be Usable to be Useful Effective design, appropriate functionality, responsive system happy users, satisfied developers Poor usability Users fail to find functionality/data Users misinterpret or misuse features Users give up in disgust (may apply to specific subsets of users) Usability is more than esthetics!

CS The Core of Usability Design: Evaluation, Iteration

CS User Interfaces in Software Processes Static textual documents are weak for specifying interactive human interfaces 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 Tools for User Interface Design/Evaluation

CS Mock-ups: a Cheap and Flexible Tool

CS Focus Groups for New Interface Ideas 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 different (potential) user populations

CS Accessibility Support for users who cannot use standard interface effectively Your team may be subject to legal/contractual requirements Example of requirements specification: The system must comply with Section 508 of the US Rehabilitation Act Good first step: build your software with popular user interface frameworks; adhere to standards User testing may not be enough

CS Usability is More than Skin Deep

CS Examples of Mental Models The desk top metaphor -- files and folders in “physical” locations The web search model -- A flat collection of pages, searched upon request Also called a conceptual model

CS Mental Models A mental model is the user’s understanding of what is going on under the hood Allows user to predict results of actions Usually quite a bit simpler than the actual system implementation Can be different from system implementation, but such divergence creates risk of user surprise

CS Interface Design is Skin Deep Appearance of information on screen and modes of control 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 Art and Science of Interface Design Interface design has a large dose of art, but there are some general principles that can be applied 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 Fitt’s law

CS Interface Functions and Objects Interface functions: actions available to the user Select part of an object Search a list or sort results View help information Manipulate on-screen objects Pan, zoom In general there are many alternative interface designs for an interface function

CS System Issues Affect Usability 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 Relevant Response Time Limits 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 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 Textual (Command Line) Interfaces Largely displaced by graphical interfaces, but still relevant in some contexts: Scripting Sometimes makes complex interactions easier Faster for certain tasks (and certain users) Easier for people with some disabilities Low bandwidth requirements