Final answer:
The analogy 'Tunnel:cave::note:song' shows a part to whole relationship, comparing tunnels as parts of caves to notes as parts of a song. This is different from an allegory or a metaphor, as it specifically reflects the relationship between an element and a larger structure.
Step-by-step explanation:
The word relationship shown in the analogy Tunnel:cave::note:song is one of part to whole. In this analogy, just as a tunnel is a part or type of cave, a note is a part of a song. This type of analogy demonstrates how individual elements relate to larger constructs or ideas.
Throughout literature, such relationships are often explored through various literary devices. For instance, Plato's Allegory of the Cave uses the concept of a cave to represent an abstract idea of human perception and knowledge. Similarly, an analogy seeks to clarify a concept by showing a relationship between two things, here showing how a single note relates to an entire song.
It's important to distinguish such relationships from metaphors or similes which make direct or indirect comparisons, as well as from allegories which are narratives with a deeper meaning or message that are not just about the relationship between individual parts and a whole.