Conceptual Model
Conceptual model is our way to see how the thing might work and how to operate over it. For example, when we see a bike, we can understand how it works in general be modeling it in our mind. Conceptual model is actually defined by 3 parts - affordance, constraints and mappings.Affordance helps to understand how basically approach the thing. Constraints help to see how the best operate over the thing.
Affordance and Contraints helps to make the conceptual model obvious. For example, scissors. There are 2 holes in it. So we can understand that they are to put something inside, like fingers. While constrains help to understand what fingers we need to put inside.
Affordance and constraints helps to build visibility, which is required to understand how the thing works and what it is for. For example, scissors have clear visibility, while handwatches with multiple are not as clear. Obvious conceptual model is required for product, if you want its design to be transparent to customers.
Design model is how the product seen by its designer. User model is how the product seen by its user.
Affordance
Each thing has some kind of affordance. For example, chair affordance is sitting, scissors affordance is cut, bed affordance is sleep, plates are for pushing, knobs are for turning etc.Affordance provides a strong clue on how to operate with thing.
Visibility
Each control over product should have clear visibility. You should be able to see what you can do with a thing, and what thing can do for you. If you don't see the way to operate it, you won't be able to do that. User should also have a feedback on each action he/she does. For example, if you press the button, you should see some feedback. If there is no feedback, you think that it's broken.Single action
Each action should control one functionality. This could be heat, sound volume, play control etc. However, there should be no button that controls volume, play controls, switch playlist and etc all in once.Principle of Mapping
Each control should be mapped to the action in convenient and easy-to-understand way. There should be no confuse how to use the control to achieve the expected result. There are multiple example of good and bad way. For example, direction forward-backward represented as left-right has a bad mapping. At the same moment, when driver turns the steering wheel left and the car start moving left is an example of good mappings. User expects a natural mapping for the thing and it's controls.Principle of Feedback
No matter how usable thing and control looks, the feedback is the necessary for any product. Feedback is basically a visibility of the change that happened due to user action. Using feedback, we could even try to understand how the bad design control or thing works, but this takes a lot of time and not everyone would like to do that.Designer should try to find the best way to improve product feedback. This means that some display might be added (either graphical or vocal display). Feedback and mapping creates the duo which increases usability a lot.
Actions
Goal is defined throught a set of intentions. Intention is a way to achieve the goal. Intention is defined through actions with the physical world. Thus to achive a goal, one needs to define the intentions how to do that, and then use actions to make intetions real.We use evaluation to understand the result of our actions.
Thus there are 2 different gulfs that separate mental state from physical state:
- gulf of execution - the difference between user intentions and the allowable actions (or how to execute those actions)
- gulf of evaluation - the difference between product state and perceived state; user should have the ability to evaluate the result of operation (either right or not)
Design Questions
Here is a list of good questions, that helps to see if design is good or not.So, how easily can one ...
- tell what actions are possible?
- determine mapping from intention to physical movement?
- perform an action?
- tell if the system is in desired state?
- determine mapping from system state to interpretation?
- tell what state the system is in?
- determine the function of the device?
