What is one of the key attributes of configuration items?

One of the key attributes of configuration items is that they are replaceable as an entity. In systems engineering, configuration items are distinct and identifiable components of a system that are under formal configuration management. This attribute emphasizes that configuration items can be swapped out or replaced without altering the overall system design. This capability is crucial for maintaining the functionality and integrity of the system while allowing for upgrades, repairs, or modifications to be made as needed.

The importance of this attribute lies in its role in ensuring that the overall system remains cohesive and operates effectively, even as individual parts may change over time. Configuration management processes help track these changes, ensuring that all stakeholders have a shared understanding of what comprises the system at any given moment.

Other options highlight characteristics that do not align with the core definition of configuration items. For example, while some items can indeed be complex or highly customizable, these features do not define their status as configuration items. Similarly, suggesting that configuration items are not under formal control undermines the essence of configuration management, which is all about maintaining formal control over changes and ensuring that each configuration item's status is clearly documented and known.