In structured logging, each event is represented by an unrestricted set of key-value pairs. This offers a variety of advantages, including simpler parsing, easier format conversion, and more flexible classification and correlation of events, even across diverse log sources.
As a counter-example, the BSD syslog format provides only a very restricted set of metadata fields in the header, while any data that is specific to the event or log source, such as username or IP address, appears as a free-form string.