Means-ends relationships are examined within the ADS, these relationships form the basis of decision making. This involves examining what needs to be done within a system and also understanding the available means for completing these ends. Vicente (1999) points out that the means-ends relations between the different levels of abstraction in the ADS are structural means-ends relations rather than action means ends relations. This means that instead of describing tasks for goals, means ends relationships focuses on the purposes of the system and the physical tools available. In complex work domains there are often many-to-many relationships, these require the user to select from a number of physical arrangements to meet a specific purpose.
In the same way one specific physical arrangement may be the only method for two independent purposes requiring the user to make decisions. In routine or highly familiar situations, the means-ends relations that must be considered
by workers are usually well established and stable. Decision making in these situations is relatively straightforward and reflects either skill or rule-based reasoning (Rasmussen et al., 1994). Naikar et al (2005) explain this well using an example of the home; people may know the effects of eating out more than once or twice a week on their savings so that making a decision about whether to eat out or not on any particular occasion may be relatively straightforward (rule based). An unfamiliar decision that will require more thought; inhabitants may need to explicitly consider all possible means-ends relations in deciding whether to accommodate an elderly parent at home or in a nursing home.
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