How Thema Is Structured

Thema has a hierarchy of subjects. There are 20 top-level categories, with varying depths of sub-categories. Each of these has a language-independent alphanumeric code and an associated heading. In some cases, they may also have an associated usage note. There are about 3000 of these subject headings. The hierarchy implies that books should be classified to the most detailed appropriate level and a book classified as – for example – AGA (History of art) is also automatically and more generally associated with the AG (Fine arts: treatments & subjects) and A (The arts) categories. The headings have been translated into about 20 languages so far. The codes can be transmitted to any partner without the meaning of the category changing. 

In addition to the headings, there are ‘qualifiers’ that can be used to refine the meaning of the main subject categories. There are six of these qualifier types: 

1. Place qualifiers – where the book is about or where the action takes place.
2. Language qualifiers – the language the book is about (and not the language the book is in).
3. Time period qualifiers – the book is about this period (a history book), or the action takes place in the period (an historical novel)
4. Educational level qualifier – the grade, specific curriculum, exam, type of education etc.
5. Interest qualifier – gives an idea of a group that may be especially interested by this title, (e.g. 15 years old and up, African-Americans, Buddhists, Lesbians etc.)
6. Style qualifiers – which are used with the arts subjects (e.g. ‘Gothic’ used with art or architecture)

Finally, there are ‘national extensions’ within the qualifiers. These are a very important part of Thema and allow for a local feel to a global scheme. The extension codes are arranged so that national extensions can be truncated to leave a meaningful ‘global level’ qualifier if the national extension is too specific. 

Thema is a post-coordinated scheme that allows meaning to be built up by using one or more subject codes plus qualifiers. This ensemble carries the ‘subject’ of the book. This approach differs from that used for BISAC subject codes, in which a single code is used to bring together different concepts to give meaning.

To illustrate this, if you were classifying a travel guide to Boston you would send the BISAC code TRV025060 – TRAVEL / United States / Northeast /New England (CT, MA, ME, NH, RI, VT). With Thema you would send two codes WTH – Travel Guides + 1KBB-US-NEMB – Boston. The post co-ordination aspect of Thema gives it a greater choice of meanings through possible combinations of codes.

This flexibility is useful for a global scheme and is also well adapted to a facetted search model within a product catalogue or online store. Subject classification provides the core context within which other search strategies can be used. It may not be visible to the end user, but it underpins the search and retrieval logic. The basic function of any subject scheme is to provide a key access point for research and discovery for consumers, to enrich product information between trading partners, to inform purchasing decisions, to enable a common language for sales reporting, to identify trends, and so on. Thema provides these things on a global level.