The following is taken from the first edition of the Set Book. We have included this because we find these characteristics helpful. We will refer to them later.

In addition to the four basic activities of design, there are three key characteristics of the interaction design process:

1 Users  should  be  involved  throughout  the development  of  the project. 

2 Specific usability and user experience goals should be identified, clearly documented and agreed upon at the beginning of the project 3  Iteration through the four activities is inevitable.

Usability and user experience goals are introduced in Unit 2 of this block, and their agreement with stakeholders is of particular importance to the 'Identifying needs and establishing requirements for the user experience' ID activity.

Iteration is only revisited briefly later in M364 so it is important you understand its meaning now, as it is central to the viewpoint of M364.

In this context, iteration means each of the four ID activities may need to be carried out more than once, depending upon the outcomes of the other activities. The following are three examples of why this situation often arises.

1 It is very difficult to understand fully the users and their needs without first having evaluated some designs with them. This is because each user has a unique and distinct personality, which results from both their experience of life and their genetic inheritance.
For this reason, you should never assume the users share your knowledge and background, because they probably do not.

2 Evaluation can result in the design or the requirements being modified; these then need evaluating again, and so on.

3 There is typically no single design that perfectly meets the needs of the users. Instead it is a matter of exploring the different design
options, making compromises as necessary. Each design needs to be evaluated, again resulting in iteration, tending towards the design that best meets the needs of the users.

Thus it is usually necessary to move between the four ID activities in a fluid and often repetitive manner.  

This makesthe ID processvery different to less flexible methodologies such as the waterfall model as described in Unit 3 of this block.  In the following section there is an activity that provides you with the opportunity to consider how one interaction designer actually applies this process.