Which engine attribute indicates the connection between the engine and Historian?

The attribute that indicates the connection between the engine and the Historian is the ConnectState attribute. This attribute is crucial because it provides a real-time status of the connection, allowing users to understand whether the engine is successfully linked to the Historian and functioning as intended. The ConnectState reflects various states, such as connected, disconnected, or attempting to connect, which are vital for diagnostic and monitoring purposes within the Historian architecture.

The other choices do not serve this specific function. For example, while attributes like Status and Connection may imply some level of connectivity or state, they do not specifically articulate the nature of the connection or its current operational state as clearly as the ConnectState does. The DataLink attribute is also unrelated to connection status, as it typically pertains to the channel through which data is exchanged rather than the connection's status itself. This makes ConnectState the most appropriate attribute for monitoring the connection status between the engine and the Historian.