Dialog Design: Introduction and Command Languages

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Dialog Design Introduction and Command Languages

• This presentation has been developed by the
  Georgia Tech HCI faculty over a period of years.
  Contributors include Gregory Abowd, Jim Foley,
  Diane Gromala, Elizabeth Mynatt, Jeff Pierce,
  Colin Potts, Chris Shaw, John Stasko and Bruce
  Walker

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Agenda

• Dialogue design styles and issues
• Command languages
• Advantages, disadvantages
• Design guidelines

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Dialog Styles

• 1. Command languages
• 2. WIMP - Window, Icon, Menu, Pointer
• 3. Direct manipulation
• 4. Speech/Natural language
• 5. Gesture, pen

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Dialog Design - Humor

• How does a user interact with the interface?

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General Issues in Choosing Dialogue Style

• Who is in control - user or computer
• Initial training required
• Learning time to become proficient
• Speed of use
• Generality/flexibility/power
• Special skills - typing
• Gulf of evaluation / gulf of execution
• Screen space required
• Computational resources required

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Command Languages

• Earliest UI interaction paradigms
• Examples
• MS-DOS shell
• UNIX shell
• dBase

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CL Characteristics

• Little or nothing is visible so
• Work primarily by recall, not recognition
• Heavy memory load
• Poor choice for novices but...

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CL Advantages

• Advantages for experts
• ?

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CL Advantages for Experts

• Speed, conciseness
• ls (hard to beat
• Can express actions beyond a limited set
• Flags, piping one command to another
• Repetition, extensibility
• Scripting, macros
• Easier implementation, less overhead
• Power
• Abstraction, wild cards

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CL Disadvangates

• Make a list if you are by yourself or in a small
  group
• Or suggest some to the class

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Next.

• Listed all you can think of? Go on to the next
  page..

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CL Disadvantages

• Error-prone
• Harder to learn
• Requires typing
• With added power, comes added responsibility and
  danger
• UNIX
• rm -r f
• Deletes every file that youhave, provides no
  feedback,and you cant get them back

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Unix Shell CL Disadvantages

• Learning takes a long time
• Hard to remember command names
• Some command names dont make sense, so have to
  memorize
• No in-progress feedback - how much longer?
• System state is invisible, and have to know which
  commands to use to get which information
• Hard to make sense of outputs, such as with ls -
  no headings, no code interpretations
• No look
• No warning if bad things are going to happen

• No universal Undo to reverse a command, have to
  know the inverse command (create directory,
  delete directory)
• Have to use man command to find desired command
• How to get help?
• Because commands are short, typos can lead to
  incorrect command
• Inconsistent flag meanings
• Inconsistent parameter orders
• Have to type a lot - touch typing needed

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CL Reflection

• Command languages are often maligned (for good
  reason)
• But increased functionality can win out over bad
  UI (e.g., UNIX)
• Try to get both
• Avoid excess functionality (comes at cost)

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CL Design Goals

• Consistency
• Good naming and abbreviations
• Doing your homework in design can help alleviate
  some of the negatives

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CL Consistency

• Provide a consistent syntax
• In general Have options and arguments expressed
  the same way everywhere
• UNIX fails!
• Commands were developed by lots of different
  people at different organizations
• No guidelines provided
• If commands long, have simple consistent
  abbreviations

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CL Syntax Be Consistent!

• Simple command list
• e.g, vi, minimize keystrokes
• Commands plus arguments
• realistic, can provide keyword parameters
• cp fromfoo tobar
• Commands plus options plus arguments
• what you usually see

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CL Order

• English SVO subject verb object
• you is assumed as the subject - imperative!
• CL S assumed (you)
• Is VO or OV better?
• delete file or file delete
• V dO iO vs. V iO dO
• print file calvin
• lpr -Pcalvin file
• Which is better?

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CL Ordering

• Keep ordering consistent
• VO (Verb Object) seems to be the most natural
• Typically need to pick where options go
• Example
• ln -s file1 file2
• Think of cp file1 file2

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CL Terminology

• Keep terminology consistent
• Same concept expressed with same options
• Useful to provide symmetric (congruent) pairings
• forward/backward
• next/prev
• control/meta

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CL Example of Congruent Pairs

• vi text editor
• w - forward word
• b - backward word
• Wouldnt f be better for forward?
• f already used
• How about fw and bw?
• Extra keystrokes

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CL Names and Abbreviations

• Specificity versus Generality
• General words
• More familiar, easier to accept
• Specific (typically better)
• More descriptive, meaningful, distinctive
• (Nonsense does surprisingly well for small set of
  commands)

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CL Abbreviations

• Abbreviations allow for faster actions
• Expert performance begins to be dominated by
  motor times such as of keystrokes
• Not good idea for novices
• (Allow but dont require)

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CL Abbreviation Strategies

• Simple truncation (works best, but conflicts)
• Vowel drop plus truncation (avoid conflicts)
• First and last letters
• First letters of words in a phrase
• Standard abbrev from other contexts
• qty, rm, bldg
• Phonics
• xqt

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CL Abbreviation Guidelines

• Use single primary rule (with single fallback for
  conflicts)
• Use fallback as little as possible
• Mark use of fallback in documentation
• Truncation is good but generates conflicts
• Fixed length is better than variable length
• Dont use abbrevs. in system output
• Can use auto-completion as alternative to
  abbreviations

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CL Abbreviations Matter...
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CL Design Affects Performance

• Terse CL Wordy CL
• Find/tooth/ -1 backward to tooth
• List/ko list all lines with ko
• Rs/ko/,/ok/ change ko to ok
• User type task completed wrong commands
• (8 of each) Terse Wordy Terse Wordy
• Inexperienced 28 42 19 11
• Familiar 43 63 18 6.4
• Experienced 74 84 9.9 5.6

All command words can be abbreviated with a
single letter.
Ledgard et al, The Natural Language of
Interactive Systems, CACM, October 1980 556-563
see also subsequent letters to the editor.
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Design New Set of Commands for vi Navigation
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All vi Commands

• Text Insertion Commands
• a Appends text after cursor.
• A Appends text at the end of the line.
• i Inserts text before cursor.
• I Inserts text at the beginning of the line.
• o Opens new line below the current line for text
  insertion.
• O Opens new line above the current line for text
  insertion.
• DEL Overwrites last character during text
  insertion.
• ESC Stops text insertion.
• Text Deletion Commands
• x Deletes current character.
• dd Deletes current line.
• dw Deletes the current word.
• d) Deletes the rest of the current sentence.
• D, d Deletes from cursor to end of line.
• P Puts back text from the previous delete.
• Changing Commands
• cw Changes characters of current word until ESC.
  
• c Changes text up to the end of the line.

• Undo Command
• u undo the last command.
• Screen Commands
• CTL/l Reprints current screen.
• CTL/L Exposes one more line at top of screen.
• CTL/E Exposes one more line at bottom of screen.
  
• CTL/F Pages forward one screen.
• CTL/B Pages back one screen.
• CTL/D Pages down half screen.
• CTL/U Pages up half screen.
• Cursor Positioning Commands
• j Moves cursor down one line, same column.
• k Moves cursor up one line, same column.
• h Moves cursor back one character.
• l Moves cursor forward one character.
• RET Moves cursor to beginning of next line.
• 0 Moves cursor to beginning of current line.
• Moves cursor to end of current line.
• SPACE Moves cursor forward one character.

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Vi Navigation Commands

• j Moves cursor down one line, same column.
• k Moves cursor up one line, same column.
• h Moves cursor back one character.
• l Moves cursor forward one character.
• RET Moves cursor to beginning of next line.
• 0 Moves cursor to beginning of current line.
• Moves cursor to end of current line.
• SPACE Moves cursor forward one character.
• nG Moves cursor to beginning of line n.
• 0 Moves the cursor to the first character of
  the line.
• n Moves cursor to beginning of line n.
• b Moves the cursor back to the beginning of the
  prev. word.
• e Moves the cursor backward to the end of the
  prev. word.
• w Moves the cursor forward to the next word.
• /pattern Moves cursor forward to next occurrence
  of pattern.
• ?pattern Moves cursor backward to next
  occurrence of pattern.
• n Repeats last / or ? pattern search.

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The End