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Configuration Item

(Alias: CI)

A component of a system that is treated as a self contained unit for the purposes of identification and change control. All configuration items (CIs) are uniquely identified by CI registration codes and version numbers. A CI may be a primitive system building block (e.g. code module) or an aggregate of other CIs (e.g. a sub-system is an aggregate of software units).

Examples of Configuration Items

The figure depicts the configuration of an underground railway environmental control system. The system has a central operation control centre and many railway stations. Each station has:

  • A local control processor (LCP) that allows operators to display and manipulate the air conditioning system and smoke extraction fans
  • A remote terminal unit (RTU) that performs the control function and
  • An integrated backup panel (IBP) that allows operators to take over manual control of the system.

For the purposes of example let's look at the configuration items identified for the remote terminal unit control software. The RTU has three components that are managed as self-contained units for the purposes of identification and change control:

  • The firmware - the operating system that runs the remote terminal unit
  • The configuration - this is a data file that determines the operation of the RTU
  • The logic - the application software that performs direct digital control functions.

These three components were identified as primitive level configuration items as they cannot be further decomposed and are managed as self-contained units. For example each logic file that is loaded into the RTU has a unique identifier and version number.

The RTU is an example of an aggregate configuration item. An RTU CI release is an aggregate of firmware, configuration and logic CIs. The station CI is another aggregate configuration item. A station CI release is an aggregate of the individual LCP, RTU and IBP CI releases.

Designating Configuration Items

The choice of aggregate and primitive level configuration items is driven by the way the development, operation and maintenance of a system is managed. For example the station CI was selected as a configuration control item because it is useful to have one revision identifier that indicates the configuration status of all control system components at that location. The revision level assigned to the station CI denotes the level of functionality available and the possible modes of communication with the operation control centre.

General guidelines for identifying configuration items are:

  • CIs are released as a unit to the customer
    Example: Mission computer, accounting package
  • CIs may be replaced as a unit in the field
    Example: Modem, Remote Terminal Unit (RTU)
  • CIs perform a meaningful stand-alone function
    Example: RTU

Member Comments


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RE Definition: Configuration Item


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