Constraints

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=__Constraints__=

Upon designing a product, designers must consider whether it is understandable to its potential users. Thus, being unaware of a designs functionality may lead to a users inability to interact with it. There are two methods that users will depend on in order to figure out how to manipulate functions within a products design. The first; affordance which as its method suggests a list of alternative actions to take in order to use a product, secondly, the constraint method which sets the restrictions on the alternative actions that can be taken upon using a product. Designers must incorporate these two principles into their designs in order to signal users.

There are four major types of constraints: physical constraint, semantic constraint, cultural constraint and logical constraint. These constraints are used in the construction of a design in order to advise users of their limitations.Further, they explain the actions which may be performed to manipulate a product’s function.

__Physical Constraint__
The use of physical constraints limit the actions that can be taken in the use of a product. Physical constraints can be perceived directly just by looking at the object itself without prior learning. The physical structure of a product is heavily considered to determine the possible actions that can be performed. Physical constraint only allows functions to be carried out by a product when the action that the user takes is correct. If the action that the user takes is incorrect, the product will not carryout the function in which it was designed for. For example, the purpose of a helmet is supposed to be worn on the head to protect the head from collision with hard surface. The shape and the physical structure of a helmet limits the user to wear the helmet in other parts of their bodies besides the head. The helmet has to be worn on the head in order to carryout the function of providing protection for the head. (Source number 1 and 2 in bibliography) A type of physical constraint is a term called forcing functions, forcing functions are proceedings that are controlled so that malfunction at one stage prevents the next step from being taken place. An example of this is starting a car, in order to start the engine you must put the ignition key into the ignition switch. It is necessary to turn the key towards the right in order to get the car started (Norman). This is an efficient force function that makes you use an object to do an operation. Forcing functions are the extreme case of strong constraints that make it easy to discover erroneous behavior(Norman).
 * Forcing Fucntion**

__Semantic Constraint__
The use of semantic constraint depends heavily on the user’s knowledge about the condition where a product is used and how it relates to the physical world. Indeed, different products are being used in different conditions to carryout their functions. Users have to depend on their tacit knowledge, which is a type of knowledge that people build up based on previous experience, to determine the actions needed to be performed under a certain condition to get functions from a product. For example, the function of a car is to transport people from a point to another. The car must be running on the road and the driver must be seated facing the front in order to see the road. The actions of driving the car on the road and sitting facing the front to operate a car would be considered as a semantic constraint. (Source number 1 and 2 in bibliography)

__Cultural Constraint__
The use of cultural constraint depends heavily on the user's culture and belief background. Different countries have different cultures and beliefs. Some cultures limit certain actions and behaviors to be performed under a certain condition to be considered as appropriate. For example, the color of red is universally perceived as the meaning to stop. Therefore traffic light systems around the world, regardless of the culture aspect, only use the red light as a signal to stop the traffic. The red light is also placed at the back of the car to signal that the car is coming to a stop. (Source number 1 and 2 in bibliography)

__Logical Constraint__
The use of logical constraint is closely related to natural mapping. Natural mapping depends on logical constraints to carry out its function. For example, the action to move a control button upwards means to increase a result. In the case of a remote control, you’ll press the button that indicates upward if you want to increase the volume and press the button that indicates downward if you want to decrease the volume. The natural mapping uses physical analogies (upward and downward) to design the buttons on the remote control and users use logic to determine which button will most likely give the result that he/she wants. Users use the logical relationship between a button and the result that it provides to decide which one to use. (Source number 1 and 2 in bibliography) There are three categories of logical constraints:
 * 1) Placement constraints
 * 2) Relative location constraints (RLOC)
 * 3) Time constraints

=__Bibliography__=

1) Donald A. Norman. 2002. The Design of Everyday Things. The MIT Press.

2) Norman, D. A. (1988). The psychology of everyday things. New York: Basic Books.

3) Unknown, Author. "Affordance and Design." __Jnd__. 2006. 28 Oct. 2006 <[|http://www.jnd.org/dn.mss/affordances_and.html>.]