Like all digital projects, HP needs to be structured through an ontology, that is, a set of rules that determine the nature of entities and their attributes. Provisionally, we have determined that the top-level distinction categorizes every pharmacopeia as reference or functional. Reference pharmacopeias, like the Ricettario Fiorentino or the theoretical writings of Mesue (explored in this DALME essay), present an idealized or normative set of medicaments, such as those that a practitioner should or could have on hand. Within this category, we divide the pharmacopeias into theoretical or pragmatic texts, the latter of which includes price lists and official pharmacopeia. Functional pharmacopeias, including apothecaries' inventories or shopping lists, describe existing or aspirational stores or collections. In functional pharmacopeias, we can see what people actually had, or wanted to have, on hand, such as what one could buy at a particular shop, or what a military operation might need (more leeches!). Within the category of functional pharmacopeia, we classify documents as inventories (leases, sales, postmortem, debt repayment, aggregate prescriptions), consumer shopping records (including normative start-up costs), and catalogs.