Transcript Improving the Design - Multimedia University

User-Interface Design &
Real-time Systems Design
“Can the user easily do what he wants to do?”
“An unresponsive real-time system may be
worse than no system at all”
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Lecture Objectives
To understand the important aspects of
user interface design
To discuss the guidelines for producing
better user interface
To understand the major issues in
designing real-time systems
To illustrate the design considerations for
real-time systems
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User Interface
The interface is the system for most users
Communication between the user and the
system
When interface is not easy, user may reject
system
Important to have more user-friendly interface
to improve usability
User training may help improve user’s
understanding and use of system
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Types of Interface
Natural Language Interface
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Types of Interface
Question and Answer Interface
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Types of Interface
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Types of Interface
Menus
Input/ Output Forms
Command-Language Interface
User interface has two main components
* Presentation language
* Action language
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Human Factors
It is important to understand the human
factors
Better understanding of skills, behaviour
and limitations can produce better and
friendlier interface
The factors:
Human Perception
Human Skills
Type of Task
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Human Perception
Visual - size, shape, color, orientation,
movement, etc
When we look at an item, we are
receiving info from all parts
The brain can efficiently process 7 chunks
(items) at a time
So when designing a screen, these factors
should be considered
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Human Skills
Understand the target user and the skill
level of the user
Education level, e.g. clerk, manager,
engineer or programmer
Computer skills - novice, average, expert
For unskilled users, user interface have to
be more robust and more help should be
available
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Types of Tasks
Communication tasks - information
transferred from producer to consumer
Dialogue tasks - user direct and control
interaction with the system
Cognitive tasks - performed once information
is obtained; associated with system function
Control tasks - allow user to control info and
cognition and order the process through
which other generic tasks occur
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General Interaction
Guidelines
Be consistent
Offer meaningful feedback
Ask for verification of any non-trivial
destructive action
Permit easy reversal of most actions
Reduce the amount of information to
memorise between actions
Seek efficiency in dialog, motion and
thought
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General Interaction
Guidelines (Continued)
Forgive mistakes
Categorize activities by function and
organise screen geography accordingly
Provide help facilities that are context
sensitive
Use simple action verbs or short verb
phrases to name commands
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Information Display
Guidelines
Display only information that is relevant to
the current context
Don’t bury the user with data, use a
presentation format that enables rapid
assimilation of information
Use consistent labels, standard
abbreviations, and predictable colours
Allow user to maintain visual context
Produce
meaningful
error
messages
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Information Display
Guidelines (Continued)
Use upper and lower case, indentation,
and text grouping to aid in understanding
Use windows to compartmentalize
different types of information
Use ‘analog’ displays to represent
information that is more easily assimilated
with this form of representation
Consider available geography of the
display screen and use it efficiently
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Data Input Guidelines
Minimize the number of input actions
required of the user
Maintain consistency between information
display and data input
Allow user to customize input
Interaction should be flexible but also
tuned to the user’s preferred mode of
input
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Data Input Guidelines
(Continued)
Deactivate commands that are
inappropriate in the context of current
actions
Let user control the interactive flow
Provide help to assist with all input
actions
Elliminate “mickey mouse” input
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Real-time Systems
Systems that are integrated with realworld devices
Generate action in response to external
events
High speed data acquisition and control
under severe time and reliability
constraints
System performance is most important
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Real-time Systems
Interfaces
Control
device
Sensors
environmental
data
control
instructions
Real-time
System
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Examples of Real-time
Systems
Aircraft avionics
Manufacturing process control
Industrial instrumentation
Intelligent buildings
Anti-lock Braking System (ABS)
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Differences in Real-time
System Development
Design of real-time system is resource
constrained
Real-time systems are compact, yet
complex
Real-time systems often work without the
presence of a human user
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Demands of Real-time
System
Information flow that is gathered or
produced on a time-continuous basis
Control information passed throughout the
system and associated control processing
Multiple instances of same transformation,
sometimes encountered in multitasking
situations
System states and the mechanism that
cause transitions between states
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Time-continuous Data
Flow
Monitored
temperature
Input ‘continuously’
Output ‘continuously’
Monitor
and adjust
temperature
level
Corrected
value
Temperature
set-point
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Extensions to Data Flow
Notation
quasi-continuous data flow
Control
process
control item
control store
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Data object that is input or output from a
process on ‘continuous’ basis
Transformer of control or “events”;
accepts control and input and produces
control as output
Control item or event; takes on a
Boolean or discrete value
Repository of control items that are to
be stored for use by one or more
processes
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Example of Data and
Control Flow
Status of each
fixture
Movement
alarm
parts status buffer
Bit string
Start/stop
flag
Monitor
fixture &
operator
interface
Operator commands
Robot
initiation
control
Operator
settings
Robot movement
record
Process
activate
Process
robot
commands
Position
commands
robot command file
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Dynamic Attributes
Interrupt handling and context switching
Response time
Data transfer rate and throughput
Resource allocation and priority handling
Task synchronization and intertask
communication
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Interrupt Handling and
Context Switching
Interrupts - external stimuli
System must respond to interrupts
Usually multiple interrupts - need to
prioritize and service most important ones
Many real-time operating systems make
dynamic calculations to monitor servicing of
interrupts, within given time constraints
Context switching - switch among tasks
Interrupt
latency - time lag before interrupt
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Interrupt Handling
Routine
Save state of interrupted program
Determine nature of the interrupt
Service interrupt
Restore state of interrupted program
Return to interrupted program
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Response Time
Time within which a system must detect an
internal or external event and respond with
an action
Usually event detection and response
generation are simple
Determining appropriate response may
involve complex, time-consuming algorithms
Context switching and interrupt latency
affects response time
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Data Transfer Rate and
Throughput
Data Transfer Rate - how fast data move
into or out of the system
Throughput - rate of output compared to
rate of input (system efficiency)
Timing and capacity is usually given by
vendors
However, overall system performance
need to consider other factors e.g. device
performance, buffer size, I/O device, etc.
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Resource Allocation and
Priority Handling
Distributed databases are preferred in
real-time systems because of multitasking
Data often processed in parallel
Concurrency control required - locking
and time stamping to ensure data
integrity
Real-time operating systems also manage
resources such as memory and processors
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Task Synchronisation
and Communication
Real-time multitasking systems must have
mechanism to synchronize and
communicate between tasks
Queuing semaphores - synchronization
and signaling items that manage traffic
Mailboxes and Messaging systems alternative to sending information
between tasks
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Conclusion
Real-time system emphasized on
performance and reliability
Fault tolerance and system restart is most
critical
Often redundancy and backup is built into
system design
Design requires additional consideration
for size, efficiency and reliability
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References
“Software Engineering: A Practitioner’s
Approach” 5th Ed. by Roger S. Pressman,
Mc-Graw-Hill, 2001
“Software Engineering” by Ian Sommerville,
Addison-Wesley, 2001
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