Mentally, classification is similar to making bricks out of wet muddy clay. It's a way to make orderly and useful the mud, the mud of the earth and the mud of your mind. So mentally when you classify, your mind trying to make order out of fluid supple mental processes. Maybe the link to Aristotle's categories will help clarify the process.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.