Ontologies

How the data of a place is cut into things and relations a model can reason about.

Between the data and the engine sits a decision about what the things are. A river model's world is reaches and flows; a city model's world is buildings with heights and uses; an agent-based model's world is agents and rules. These choices are the model's ontology, and most engines carry one without saying so. Joining two models is mostly the work of reconciling two of them.

The choices matter because the world does not arrive in pieces. A "thing" is a cluster of tightly entangled relationships that is useful to name because it is roughly separate from other clusters: a dog, a watershed, a government. People are very good at recognising such clusters, and the categories they form are graded rather than sharp, with some members more typical than others (prototype theory; George Lakoff, Women, Fire, and Dangerous Things). John Muir, in My First Summer in the Sierra: "When we try to pick out anything by itself, we find it hitched to everything else in the universe." A model has to pick things out anyway. See the term entry Ontology.

This shelf holds the data models and standards that twins are built on, the papers that propose ways to order the subsystems of a place or a planet, methods for building a vocabulary up into a knowledge graph in order (reviewed here: the book Ontology Pipeline), and tools that build or discover vocabularies. It is the thinnest layer of the stack on this site and in the field, and the one where new entries are most welcome.

staging: drafts and proposals shown