Civil Engineering Reference
In-Depth Information
Total system
Sub-system
Function unit
Sub-assembly
Component
Functional
Purpose
1. PS have train for detachment
1
1
5. PS justify why line requested
Abstract
Function
5
5
10
10.Signaller accepts/rejects block requests
Generalised
Function
2. PS staff
call
signal box
2
2
Physical
Function
9. Signaller requests PS name
Physical Form
9
9
3. Signaller
states
who they are
8. PS request duration of block
3
3
4
4
8
8
6
6
7
7
6. PS state which
line to be blocked
Key:
7. PS staff request when to be blocked
4. Platform staff
state
who they
are and location
= Platform staff
= Signaller
FIGURE 36.2 Decomposition space for rail signaling task.
7. Platform staff request when to be blocked
8. Platform staff request duration of block
9. Signaler requests platform staff name
10. Signaler accepts
rejects block requests
/
36.6.3.8 GOMS (Card et al., 1983)
The GOMS technique is part of a family of HCI techniques that is used to provide a description of human
performance in terms of the user's goals, operators, methods, and selection rules. GOMS attempts to
define the user's goals, decompose these goals into subgoals, and demonstrate how the goals are achieved
through user interaction. GOMS can be used to provide a description of how a user performs a task, to
predict performance times, and to predict human learning. The GOMS techniques are based upon the
assumption that the user's interaction with a computer is similar to solving problems. Problems are
broken down into subproblems, and these subproblems are broken down further. Four basic components
of human interaction are used within the GOMS technique. These are as follows:
1. Goals — The goal represents exactly what the user wishes to achieve through the interaction. The
goals are decomposed until an appropriate stopping point is achieved
2. Operators — The operators are the motor or cognitive actions that the user performs during the
interaction. The goals are achieved through performing the operators
3. Methods — The methods describe the user's procedures for accomplishing the goals in terms of
operators and subgoals. Often there are more than one set of methods available to the user
4. Selection rules — When there is more than one method for achieving a goal available to a user,
selection rules highlight which of the available methods should be used
36.6.3.9 Hierarchical Task Analysis (Annett et al., 1971)
Hierarchical task analysis (HTA) is perhaps the most widely used of all HF techniques. Developed in
order to analyze complex tasks, such as those found in the chemical processing and power generation
industries (Annett, 2004), HTA involves describing tasks by breaking them down into a hierarchy of
goals, operations, and plans. Tasks are broken down into hierarchical set of task goals and component
subtasks and the plans used to dictate the performance of the tasks and subtasks are specified. One of
the main reasons behind the enduring popularity of the technique is its flexibility and scope for
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