Corpus formats

Corpus formats

Annif uses different kinds of corpora. This document specifies the formats.

Full-text document corpus

The full text corpus is a directory with UTF-8 encoded text files that have the file extension .txt.

The directory may also contain subject files that list the assigned subjects for each file. The file name is the same as the document file, but with the file extension .key. For example, document1.txt may have a corresponding subject file document1.key. Subject files come in two formats:

Simple subject file format

This file lists subject labels, UTF-8 encoded, one per line. For example:

networking
computer science
Internet Protocol

Note that the labels must exactly match the preferred labels of concepts in the subject vocabulary.

This format corresponds to the Maui topic file format.

Extended subject file format

This is otherwise similar to the simple subject file format, but the subject file is now a UTF-8 encoded TSV (tab separated values) file with the file extension .tsv, where the first column contains a subject URI and the second column its label. For example:

<http://example.org/thesaurus/subj1>	networking
<http://example.org/thesaurus/subj2>	computer science
<http://example.org/thesaurus/subj3>	Internet Protocol

Any additional columns beyond the first two are ignored.

When using this format, subject comparison is performed based on URIs, not the labels. Since URIs are more persistent than labels, this ensures that subjects can be matched even if the labels have changed in the subject vocabulary.

Subject corpus as a directory

A subject corpus lists the available subjects (typically defined in a controlled vocabulary) together with text that is representative of that subject. The text may be gathered e.g. from metadata records. A subject corpus is represented as a directory with UTF-8 encoded text files with the extension .txt. Each file has the following structure:

• The first line contains the URI and label of the subject, separated by a single space
• Starting with the second line, there is some text related to the subject. It is recommended that the text starts with the label of the concept itself on the first line (second line of the file) and further lines are each based on a single document.

Here is an example from the YSO/Finna.fi corpus:

http://www.yso.fi/onto/yso/p10088 municipal boards
municipal boards
Content of municipal strategy papers : comparison of five Finnish and five Canadian municipalities' strategies
The Swedish local government act
When municipalities lead co-production : Lessons from a Danish case study

Subject vocabulary as TSV

A subject vocabulary lists the available subjects in a controlled vocabulary. The simple format only specifies URIs and labels for concepts. The vocabulary file file is UTF-8 encoded TSV (tab separated values) file with the file extension .tsv, where the first column contains a subject URI and the second column its label. The format is the same as the extended subject file format for documents, specified above. For example:

<http://example.org/thesaurus/subj1>	networking
<http://example.org/thesaurus/subj2>	computer science
<http://example.org/thesaurus/subj3>	Internet Protocol

Subject vocabulary as SKOS

A subject vocabulary can also be given as a SKOS/RDF file. All common RDF serializations (i.e. those supported by rdflib) are supported, including RDF/XML, Turtle and N-Triples.

Document corpus as a TSV file

A document corpus can be given in a single UTF-8 encoded TSV file. This format is especially useful for metadata about documents, when only titles are known, or for very short documents. The first column contains the text of the document (e.g. title or title + abstract) while the second column contains a whitespace-separated list of subject URIs for that document. For example:

RFC 791: Internet Protocol	<http://example.org/thesaurus/subj1> <http://example.org/thesaurus/subj3>
RFC 1925: The Twelve Networking Truths	<http://example.org/thesaurus/subj1> <http://example.org/thesaurus/subj2>
Go To Statement Considered Harmful	<http://example.org/thesaurus/subj2>

Note that it is also possible to separate the subjects with tabs, thus creating a variable number of columns.