Classicists working on digital projects that involve data are encouraged to link their data to the semantic web. If you are new to the topic, start here (Linked open data).

In thinking about new vocabularies, whether for subjects, predicates, or objects of triples, one should begin with a survey of what already exists. By using one another's vocabularies, we reinforce the interoperability, and therefore utility, of our data. And it saves us the time needed to invent a taxonomy.

Sets of RDF vocabularies tend to fall in two groups: (1) terms for items, persons, concepts, and other resources and (2) terms for the relations that hold between resources. The first group correspond to what many scholars call controlled vocabulary, and they frequently show up as the subjects and objects of triples. The second corresponds to the vocabularies used in ontologies (e.g., RDFS, OWL, SKOS), and frequently show up as the predicates of triples.

Resources (names of things; ideal for subjects and objects of triples)

These projects listed below rely not merely upon a unique identification system, but one rooted in IRIs, whether URL-based or URNs.

General

Wikipedia

DBPedia

Freebase

An extensive list of datasets is maintained by ckan's Data Hub, and is an excellent place to look for controlled vocabularies.

Writing (texts, bibliography, works, text manifestations)

Text/object data

Vocabularies for:

Geography

People

The Standards for Networking Ancient Prosopographies project is now curating a virtual authority of ancient people using RDF exports from many other major digital prosopographies.

Other major person-data or prosopographical resources include:

Person data

Vocabularies for?

occupation

titulature

status

ethnicity

relationships (e.g. SNAP)

Objects

Topics

Ontologies (terms for relationships; ideal for predicates of triples)

General

See a list of others here. See here for a visual map.

Writing (texts, bibliography, works, text manifestations)

It is helpful to understand something about the hierarchy of texts (such as the one adopted by Functional Requirements for Bibliographic Records [FRBR]). Vocabularies describing ancient works in the abstract (under FRBR called works) will take a different approach than ones describing manuscripts, papyri, ostraca, etc. (under FRBR called items)

Geography

For other projects that use controlled vocabularies for linked open data, see the category listing as well as Very clean URIs.