3. 定義

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3. Definitions
For the purposes of this part of IEC 60300, the definitions given in IEC 60050 (191), some of which are reproduced below, together with following definitions, apply.  

3.1 Item, entity
any part, component, device, sub-system, functional unit, equipment or system that can be individually considered.  
NOTE.  An item may consist of hardware, software or both, and may also in particular cases, include people.
[IEV 191-01-01]

3.2 System set of interrelated or interacting elements.
[ISO 9000:2000]
NOTE 1.  In the context of dependability, a system will have
a)  a defined purpose expressed in terms of required functions, and
b) stated conditions or operation/use.
NOTE 2.  The concept of a system is hierarchical.

3.3 Component
item on the lowest level considerated in the analysis.  

3.4 Allocation
procedure applied during the design of an item intended to apportion the requirements for performance measures for an item to its sub-items according to given criteria.  

3.5 Failure
termination of the ability of an item to perform a required funciton.  
NOTE 1.  After failure the item has a fault.  
NOTE 2. 'Failure' is an event, as distinguished from 'fault', which is a state.  
[IEV 191-04-01]

3.6 Fault
state of an item characterized by inability to perform a required function, excluding the inability during preventive maintenance or other planned actions, or due to lack of external resources.  
NOTE.  A fault is often the result of a failure of the item itself, but may exist without prior failure.
[IEV 191-05-01]