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Designing the User Interface:

Strategies for Effective Human-Computer Interaction

Fifth Edition

Ben Shneiderman & Catherine Plaisant

in collaboration with
Maxine S. Cohen and Steven M. Jacobs

CHAPTER 7:
Command and Natural Languages

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The Basic Goals of Language Design

Precision
Compactness
Ease in writing and reading
Speed in learning
Simplicity to reduce errors
Ease of retention over time

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Languages allow for communication and problem solving

Particularly: computer languages

We need a language to be : precise, compact, …

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Higher-Level Goals of Language Design

Close correspondence between reality and the notation
Convenience in carrying out manipulations relevant to user's tasks
Compatibility with existing notations
Flexibility to accommodate novice and expert users
Expressiveness to encourage creativity
Visual appeal

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The Egyptian hieroglyphs of 5,000 years ago were a tremendous advance because standard notations facilitated communica¬

tion across space and time. Eventually, languages with a small alphabet and rules of word and sentence formation dominated because of the relative ease of

learning,writing, and reading them. Inaddition to these natural languages,spe¬

cial languages for mathematics, music, and chemistry emerged because they

facilitated communication and problemsolving. Inthe twentieth century, novel

notations were created for such diverse domains as dance, knitting, higher

forms of mathematics,logic, and DNAmolecules.

The basic goals of language design are:

• Precision

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Functionality to Support User’s Tasks

Users do wide range of work:

text editing
electronic mail
financial management
airline or hotel reservations
inventory
manufacturing process control
gaming

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Functionality to Support User’s Tasks (cont.)

Designers should

determine functionality of the system by studying users' task domain
create a list of task actions and objects
abstract this list into a set of interface actions and objects
represent low-level interface syntax
create a table of user communities and tasks, with expected use frequency
determine hierarchy of importance of user communities (i.e. prime users)
evaluate destructive actions (e.g. deleting objects) to ensure reversibility
identify error conditions and prepare error messages
allow shortcuts for expert users, such as macros and customizing system parameters

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FIGURE 7.1 Transition diagram indicating user inputs with an "i" and computer outputs with an "o."This relatively simple diagram shows only a portion of the system; complete

transition diagrams may comprise many pages. (Courtesy of Robert J. K. Jacob,

Naval Research Laboratory,Washington, D.C.)

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Command-Organization Strategies

A unifying interface concept or metaphor aids

learning

problem solving

retention

Designers often err by choosing a metaphor closer to machine domain than to the user's task domain.

Simple command set

Each command is chosen to carry out a single task. The number of commands match the number of tasks.

For small number of tasks, this can produce a system easy to learn and use.

E.g. the vi editor of Unix.

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Several strategies for command organization have emerged. A unifying inter¬

face concept or metaphor aids learning, problem solving, and retention. Elec¬

tronic-mail enthusiasts conduct lively discussions about the metaphoric merits of such task-related objects as file drawers, folders, documents, memos, notes,

letters, or messages. They debate the appropriate interface actions (CREATE,

EDIT, COPY, MOVE, DELETE) and the choice of action pairs such as

LOAD/SAVE (too much in the computer domain), READ/WRITE (acceptable

for letters,butawkwardfor file drawers), or OPEN/CLOSE(acceptablefor fold¬

ers, but awkward for notes).

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retention : retention of users and perpetuating their interest in unsing app

a metaphor = استعارة

a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.

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Command plus arguments/options

Command plus arguments

Follow each command by one or more arguments that indicate objects to be manipulated, e.g.

COPY FILEA, FILEB

DELETE FILEA

PRINT FILEA, FILEB, FILEC

Keyword labels for arguments are helpful for some users, e.g.

COPY FROM=FILEA TO=FILEB.

Commands may also have options to indicate special cases, e.g.:

PRINT/3,HQ FILEA

PRINT (3, HQ) FILEA

PRINT FILEA -3, HQ

to produce 3 copies of FILEA on the printer in the headquarters building.

Error rates and the need for extensive training increase with the number of possible options.

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headquarters building

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The Benefits of Structure

Human learning, problem solving, and memory are greatly facilitated by meaningful structure.

Beneficial for

task concepts

computer concepts

syntactic details of command languages

Consistent Argument Ordering

Inconsistent order of arguments Consistent order of arguments

SEARCH file no, message id SEARCH message id, file no

TRIM message id, segment size TRIM message id, segment size

REPLACE message id, code no REPLACE message id, code no

INVERT group size, message id INVERT message id, group size

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Hierarchical command structure

The full set of commands is organized into a tree structure

5x3x4 = 60 tasks with 5 command names and 1 rule of formation

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In this option, the set of commands is organized into a tree structure, like a menu tree. The first level might be the command action, the second might be an object argument, and the third might be a destination argument:

Action	Object	Destination
CREATE	File	File
DISPLAY	Process	Local printer
REMOVE	Directory	Screen
COPY	Remote printer
MOVE

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Symbols versus Keywords

Command structure affects performance

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Symbol Editor	Keyword Editor
FIND:/TOOTH/;-1	BACKWARD TO "TOOTH"
LIST;10	LIST 10 LINES
RS:/KO/,/OK/;*	CHANGE ALL "KO" TO "OK"

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Naming and Abbreviations

There is often a lack of consistency or obvious strategy for construction of command abbreviations.

Specificity Versus Generality

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Infrequent, discriminating words	insert	delete
Frequent, discriminating words	add	remove
Infrequent, non-discriminating words	amble	perceive
Frequent, non-discriminating words	walk	view
General words (frequent, nondiscriminating)	alter	correct
Non-discriminating non-words (nonsense)	GAC	MIK
Discriminating non-words (icons)	abc-adbc	abc-ab

In a papcr-and-pencil test, subjects studied one of seven sets of commands

(Black and Moran, 1982). All seven versions of two of the commands—the

commands for insertingand deleting text—are shown here:…

The "infrequent, discriminating" commandset resultedinfaster learningand

superior recall than other command sets. The general words were correlated

with the lowest performance. The nonsense words did surprisingly well, sup¬

porting the possibility that, with small command sets, distinctive names are

helpfuleven if they are not meaningful.

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Definitions of amble

noun

a walk at a slow, relaxed pace, especially for pleasure.

a peaceful riverside amble

verb

walk or move at a slow, relaxed pace.

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Six Potential Abbreviation Strategies

Simple truncation: The first, second, third, etc. letters of each command.

Vowel drop with simple truncation: Eliminate vowels and use some of what remains.

First and last letter: Since the first and last letters are highly visible, use them.

First letter of each word in a phrase: Use with a hierarchical design plan.

Standard abbreviations from other contexts: Use familiar abbreviations.

Phonics: Focus attention on the sound.

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Guidelines for using abbreviations

Ehrenreich and Porcu (1982) offer this set of guidelines:

A simple primary rule should be used to generate abbreviations for most items; a simple secondary rule should be used for those items where there is a conflict.
Abbreviations generated by the secondary rule should have a marker (for example, an asterisk) incorporated in them.
The number of words abbreviated by the secondary rule should be kept to a minimum.
Users should be familiar with the rules used to generate abbreviations.
Truncation should be used because it is an easy rule for users to comprehend and remember. However, when it produces a large number of identical abbreviations for different words, adjustments must be found.
Fixed-length abbreviations should be used in preference to variable-length ones.
Abbreviations should not be designed to incorporate endings (ING, ED, S).
Unless there is a critical space problem, abbreviations should not be used in messages generated by the computer and read by the user.

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Command-language guidelines

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Natural Language in Computing

Natural-language interaction

Natural-language queries and question answering

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Natural-language interaction (NLI) might be defined as the operation of computers

by people using a familiar natural language (such as English) to give instructions and receive responses. With NLI, users do not have to learn command syntax or select from menus

Since general interaction is difficult to support, some designers have pursued a

more limited goal of natural-language queries (NLQ) against relational databases.

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Natural Language in Computing

Text-database searching

Natural-language text generation

Adventure games and instructional systems

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Text-database searching is a growing application for natural-language enthusiasts

who have developed filters and parsers for queries expressed in natural language (Lewis and Jones, 1996).

Natural-language text generation (NLTG) includes simple tasks, such as the

preparation of structured weather reports ("80% chance of light rain in northern suburbs by late Sunday afternoon")….. Generated reports from structured databases can be sent out automatically, while timely spoken reports can be made available over the telephone inmultiple languages.

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Natural Language in Education

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CognitiveTutor traces student progress in mastering skills and concepts, then assigns individually tuned problems Communicating with students via Natural Language