Attribute	Attribute Meaning
alive_count	The total number of currently active DataWriters that write the Topic read by the DataReader. This count increases when a newly matched DataWriter asserts its liveliness for the first time or when a DataWriter previously considered to be not alive reasserts its liveliness. The count decreases when a DataWriter considered alive fails to assert its liveliness and becomes not alive, whether because it was deleted normally or for some other reason.
not_alive_count	The total count of currently DataWriters that write the Topic read by the DataReader that are no longer asserting their liveliness. This count increases when a DataWriter considered alive fails to assert its liveliness and becomes not alive for some reason other than the normal deletion of that DataWriter. It decreases when a previously not alive DataWriter either reasserts its liveliness or is deleted normally.
alive_count_change	The change in the alive_count since the last time the listener was called or the status was read.
not_alive_count_change	The change in the not_alive_count since the last time the listener was called or the status was read.
last_publication_handle	Handle to the last DataWriter whose change in liveliness caused this status to change.

The liveliness of one or more DataWriter that were writing instances have become "active" or "inactive"