Data Model

Entity Types and Ontology

Loosely following "Functional Requirements for Bibliographic Records" (FRBR), but removing the "manifestation" abstraction, and favoring files (digital artifacts) over physical items, the primary bibliographic entity types are:

  • work: representing an abstract unit of creative output. Does not contain any metadata itself; used only to group release entities. For example, a journal article could be posted as a pre-print, published on a journal website, translated into multiple languages, and then re-published (with minimal changes) as a book chapter; these would all be variants of the same work.
  • release: a specific "release" or "publicly published" version of a work. Contains traditional bibliographic metadata (title, date of publication, media type, language, etc). Has relationships to other entities:
    • child of a single work (required)
    • multiple creator entities as "contributors" (authors, editors)
    • outbound references to multiple other release entities
    • member of a single container, for example a journal or book series
  • file: a single concrete, fixed digital artifact; a manifestation of one or more releases. Machine-verifiable metadata includes file hashes, size, and detected file format. Verified URLs link to locations on the open web where this file can be found or has been archived. Has relationships:
    • multiple release entieis that this file is a complete manifestation of (almost always a single release)
  • fileset: a list of muliple concrete files, together forming complete release manifestation. Primarily intended for datasets and supplementary materials; could also contain a paper "package" (source file and figures).
  • webcapture: a single snapshot (point in time) of a webpage or small website (multiple pages) which are a complete manifestation of a release. Not a landing page or page referencing the release.
  • creator: persona (pseudonym, group, or specific human name) that has contributed to one or more release. Not necessarily one-to-one with a human person.
  • container (aka "venue", "serial", "title"): a grouping of releases from a single publisher.

Note that, compared to many similar bibliographic ontologies, the current one does not have entities to represent:

  • physical artifacts, either generically or specific copies
  • funding sources
  • publishing entities
  • "events at a time and place"

Each entity type has it's own relations and fields (captured in a schema), but there are are also generic operations and fields common across all entities. The API for creating, updating, querying, and inspecting entities is roughly the same regardless of type.

Identifiers and Revisions

A specific version of any entity in the catalog is called a "revision". Revisions are generally immutable (do not change and are not editable), and are not normally referred to directly. Instead, persistent "fatcat identifiers" can be created, which "point to" a single revision at a time. This distinction means that entities referred to by an identifier can change over time (as metadata is corrected and expanded). Revision objects do not "point" back to specific identifiers, so they are not the same as a simple "version number" for an identifier.

Identifiers also have the ability to be merged (by redirecting one identifier to another) and "deleted" (by pointing the identifier to no revision at all). All changes to identifiers are captured as an "edit" object. Edit history can be fetched and inspected on a per-identifier basis, and any changes can easily be reverted (even merges/redirects and "deletion").

"Work in progress" or "proposed" updates are staged as edit objects without updating the identifiers themselves.

Controlled Vocabularies

Some individual fields have additional constraints, either in the form of pattern validation ("values must be upper case, contain only certain characters"), or membership in a fixed set of values. These may include:

  • license and open access status
  • work "types" (article vs. book chapter vs. proceeding, etc)
  • contributor types (author, translator, illustrator, etc)
  • human languages
  • identifier namespaces (DOI, ISBN, ISSN, ORCID, etc; but not the identifiers themselves)

Other fixed-set "vocabularies" become too large to easily maintain or express in code. These could be added to the backend databases, or be enforced by bots (instead of the system itself). These mostly include externally-registered identifiers or types, such as:

  • file mimetypes
  • identifiers themselves (DOI, ORCID, etc), by checking for registration against canonical APIs and databases

Global Edit Changelog

As part of the process of "accepting" an edit group, a row is written to an immutable, append-only table (which internally is a SQL table) documenting each identifier change. This changelog establishes a monotonically increasing version number for the entire corpus, and should make interaction with other systems easier (eg, search engines, replicated databases, alternative storage backends, notification frameworks, etc.).