Design of Everyday Things Excerpt - Chapter 4 Contraints Discoverability & Feedback

My notes with reference to this page: https://medium.com/my-little-bookshelf/part-1-the-design-of-everyday-things-revised-expanded-edition-book-summary-key-points-3a8e498dffaa

Knowledge in the world includes

• perceived affordances
• signifiers
• the mappings between the parts that appear to be controls or places to manipulate and the resulting actions
• physical constraints that limit what can be done

Knowledge in the head includes

• conceptual models
• cultural, semantic, and logical constraints on behavior
• analogies between the current situation and previous experiences with other situations

Four Kinds of Constraints: Physical, Cultural, Semantic, and Logical 

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.


Physical Constraints

• Physical limitations constrain possible operations - or, at least, desired actions can be made obvious.
• Physical constraints are made more effective and useful if they are easy to see and interpret, for then the set of actions is restricted be- fore anything has been done.

- Issues in Physical Constraints - such as Legacy problem - using the existing standard (e.g. batteries)  physical constraint is too subtle (USB plug) (p.127) 

- Good example of physical constraint: the push bar at exit door offers both visible affordances that act as physical constraints on the action, and also a visible signifier, unobstrusively specifying what to do and where to do. (p.60)

Cultural Constraints

• Cultural issues are at the root of many of the problems we have with new machines: there are as yet no universally accepted conventions or customs for dealing with them 
• There are scripts (rules) to guide the behaviors.
• Likely to change with time.

Semantic Constraints

• Semantics is the study of meaning. Semantic constraints are those that rely upon the meaning of the situation to control the set of possible actions. 
• New technologies and time can change the meanings of things. And creative people continually change how we interact with our technologies and one another. 

Logical Constraints

• There are no physical or cultural principles here; rather, there is a logical relationship between the spatial or functional layout of components and the things that they affect or are affected by.

The focus on aesthetics may blind the designer to the lack of usability. (Figure 1.4, p. 17) Appearances can deceive. Some designers like spare, neat, modern design to a fault. (p.137)

Constraints that Force the Desired Behavior

Forcing functions

• A form of physical constraint: situations in which the actions are constrained so that failure at one stage prevents the next from happening, e.g. a vehicle won't start without the authentication proved by possession of the key.
• Forcing functions are the extreme case of strong constraints that can prevent inappropriate behavior.

Interlocks

• Forces operations to take place in proper sequence, e.g., An interlock prevents the transmission from leaving the Park position unless the car’s brake pedal is depressed.

Lock-Ins 

• Keeps an operation active, preventing someone from prematurely stopping it, e.g. This lock-in dialogue window on PC makes it difficult to exit a program without either saving the work or consciously saying not to. Notice that it is politely configured so that the desired operation can be taken right from the message.

Lockouts 

• Whereas a lock-in keeps someone in a space or prevents an action until the desired operations have been done, a lockout prevents someone from entering a space that is dangerous, or prevents an event from occurring, e.g. a specialized cap on a container for drug and toxic substances.

Conventions, Constraints, and Affordances 

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.

Consistency in design is virtuous. It means that lessons learned with one system transfer readily to others. On the whole, consistency is to be followed. 

If a new way of doing things is only slightly better than the old, it is better to be consistent. But if there is to be a change, everybody has to change. Mixed systems are confusing to everyone. 

When a new way of doing things is vastly superior to another, then the merits of change outweigh the difficulty of change. Just because something is different does not mean it is bad. If we only kept to the old, we could never improve.

Standardisation 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: standardise what has to be kept in the head. The standards should reflect the psychological conceptual models, not the physical mechanics. Standards simplify life for everyone, but they tend to hinder future development.