This blog has contained several versions of ontology definitions (here and here), but I've never seen one in the form of a limerick before, and I couldn't resist quoting it. This is by Margie Hlava, and all credit to her and to her company, Access Innovations, for creating a daily blog about taxonomy (imagine having to write it - it gets to three o'clock in the afternoon and you still haven't had a taxonomic thought of the day!). But not only that, to define ontology no less intelligibly than authors who aren't constrained by putting it into verse is quite some achievement. Thanks, Margie! If you don't know the Access Innovations Taxodiary daily blog, it is well worth reading.
Taxonomy or controlled vocabulary;
The naming is quite arbitrary.
Even an ontology
Is not really philosophy
But a structure for the words to carry.
– Margie Hlava