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These four classes of constraints—physical, cultural, semantic, and logical—seem to be universal, appearing in a wide variety of situations.
Constraints are powerful clues, limiting the set of possible actions. The thoughtful use of constraints in design lets people readily determine the proper course of action, even in a novel situation.
Four Kinds of Constraints: Physical, Cultural, Semantic, and Logical
What are the four kinds of constraints?
corporate thinking:
Organizational bias?
Semantic constraints are those that rely upon the meaning of the situation to control the set of possible actions.
Semantic constraints rely upon our knowledge of the situation and of the world.
Affordances, signifiers, mappings, and constraints can simplify our encounters with everyday objects. Failure to properly deploy these cues leads to problems.
Known cultural norms can create comfort and harmony. Unknown norms can lead to discomfort and confusion.
The lack of clear communication among the people and organizations constructing parts of a system is perhaps the most common cause of complicated, confusing designs.
A usable design starts with careful observations of how the tasks being supported are actually performed, followed by a design process that results in a good fit to the actual ways the tasks get performed.
This is the definition of task analysis. How is this related to tkinter and python as a whole? How can task analysis be incorporated into software?
human-centered design (HCD),
Encompasses task analysis
Nonetheless, there are no commercial tools available to make it easy to implement these ideas in the home.
Business idea?
Forcing functions are a form of physical constraint: situations in which the actions are constrained so that failure at one stage prevents the next step from happening.
Forcing functions are the extreme case of strong constraints that can prevent inappropriate behavior.
An interlock forces operations to take place in proper sequence.
A lock-in keeps an operation active, preventing someone from prematurely stopping it.
a lockout prevents someone from entering a space that is dangerous, or prevents an event from occurring.
Conventions are a special kind of cultural constraint.
Although conventions provide valuable guidance for novel situations, their existence can make it difficult to enact change:
Standardization is indeed the fundamental principle of desperation: when no other solution appears possible, simply design everything the same way, so people only have to learn once.
If you can’t put the knowledge on the device (that is, knowledge in the world), then develop a cultural constraint: standardize what has to be kept in the head.
standards should reflect the psychological conceptual models, not the physical mechanics.
Real, natural sound is as essential as visual information because sound tells us about things we can’t see, and it does so while our eyes are occupied elsewhere.
Error occurs for many reasons. The most common is in the nature of the tasks and procedures that require people to behave in unnatural ways—staying alert for hours at a time, providing precise, accurate control specifications, all the while multitasking, doing several things at once, and subjected to multiple interfering activities.
“Swiss cheese model of accidents” (shown in Figure 5.3 of this chapter on page 208, and discussed in more detail there).
Transactional leafers put out fires with root cause analysis. Adavanced leafers consider FAE and apply the swiss cheese model.
When root cause analysis discovers a human error in the chain, its work has just begun: now we apply the analysis to understand why the error occurred, and what can be done to prevent it.
Root cause analysis is intended to determine the underlying cause of an incident, not the proximate cause.
When people err, change the system so that type of error will be reduced or eliminated. When complete elimination is not possible, redesign to reduce the impact.
When many people all have the same problem, shouldn’t another cause be found? If the system lets you make the error, it is badly designed.
Cultures that encourage and commend violations set poor role models.
A slip occurs when a person intends to do one action and ends up doing something else.
There are two major classes of slips: action-based and memory-lapse.
In action-based slips, the wrong action is performed.
In lapses, memory fails, so the intended action is not done or its r...
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A mistake occurs when the wrong goal is established or the wrong plan is formed. From that point on, even if the actions are executed properly they are part of the error, because the actions themselves are inappropriate—they are part of the wrong plan. With a mistake, the action that is performed matches the plan: it is the plan that is wrong.
Mistakes have three major classes: rule-based, knowledge-based, and memory-lapse.
Errors can be understood through reference to the seven stages of the action cycle
Mistakes are errors in setting the goal or plan, and in comparing results with expectations—the higher levels of cognition.
An interesting property of slips is that, paradoxically, they tend to occur more frequently to skilled people than to novices.
A good way to judge the quality of a person for tenant screening or employment considerations.
There are several ways to combat memory-lapse errors. One is to minimize the number of steps; another, to provide vivid reminders of steps that need to be completed. A superior method is to use the forcing function
A mode error occurs when a device has different states in which the same controls have different meanings: we call these states modes.
Mistakes result from the choice of inappropriate goals and plans or from faulty comparison of the outcome with the goals during evaluation.
people tend to rely upon remembered experiences rather than on more systematic analysis.
three modes of behavior: skill-based, rule-based, and knowledge-based.
Skill-based behavior occurs when workers are extremely expert at their jobs, so they can do the everyday, routine tasks with little or no thought or conscious attention.
Rule-based behavior occurs when the normal routine is no longer applicable but the new situation is one that is known, so there is already a well-prescribed course of action: a rule.
Knowledge-based procedures occur when unfamiliar events occur, where neither existing skills nor rules apply. In this case, there must be considerable reasoning and problem-solving.
In both rule-based and knowledge-based situations, the most serious mistakes occur when the situation is misdiagnosed.
When root cause analysis stops at a human.
Rule-based mistakes are difficult to avoid and then difficult to detect. Once the situation has been classified, the selection of the appropriate rule is often straightforward.
The design challenge is to present the information about the state of the system (a device, vehicle, plant, or activities being monitored) in a way that is easy to assimilate and interpret, as well as to provide alternative explanations and interpretations.
