What’s a thesaurus?

We recently released a new version of Atramhasis (Atramhasis v0.6.0 released), our web based thesaurus editor. But what is a thesaurus and why would a heritage organisation want one?

Our colleagues at Historic England define a thesaurus as A structured wordlist used to standardize terminology. It is used to assist in indexing and retrieving information within databases that make use of the same terminology. A lot of opportunities arise from structuring related terms.

First of all, it is possible to express equivalencies. Defining what terms are equivalent makes it easier to find what one is looking for. This used to be done by stating that two terms are synonyms. Nowadays it’s more common to state that both terms are verbal expressions of the same concept. While before we would have stated that Jugendstil is equal to Art Nouveau, today we would say that there is a concept of a certain artistic style that is labelled with both Jugendstil and Art Nouveau. A fairly subtle difference that mainly impacts how you interact with thesauri.

Secondly, there are hierarchical relationship. Typically this is done by stating that one term is broader than another and correspondingly that the other term is narrower than the first one. This makes it possibkme in a thesaurus to state that a cathedral is a church and that a church is a religious building. From this we can conclude that cathedrals are religious buildings as well. It is important to note that not all hierarchical relations in thesauri are of the is a type. Is part of and Is an instance of relations exist as well. They do complicate certain matters, so be careful when considering them. Consult On the composition of ISO 25964 hierarchical relations (BTG, BTP, BTI) to see how they affect the whole of the relations between terms in your thesaurus.

The final type of relationship is the associative relationship. This is the softest relationship, stating that two terms or concepts are related. This might be coal mine is related to miner’s houses because in Flanders every coal mine had it’s own little town where all the mineworkers lived together.

One other important aspect of thesauri is that they allow defining a scope note. This is a written definition of the concept and how it should be used in databases. It’s a critical feature that allows users to evaluate if a certain concept actually means what they think it means. Over the years, we have found that asking experts to define concepts they thought were self-evident has caused heated discussions. As long as you don’t define what something means everyone can use a concept in the way they want to use it and ignore the fact that not everyone might share their opinion.

So, thesauri allow us to reach consenus on the meaning of certain concepts and share our knowledge about these concepts with the outside world (that’s why we publish them as open data). But we do have another, very pratical, reason for building and maintaining them. We use these controlled to help indexing our main databases and information systems. When you go searching for fountains in our inventory management system, our thesaurus is used. When the inventory receives the query for fountains it checks if it’s actually in the thesaurus. If not, no record can be indexed with that term, so it stops the search. If it is, the system checks if there are more specific version of fountains present in the thesaurus. In this case, there’s also a concept of water tricks that is defined as a specific type of fountain. So, when our inventory management systems answers you query for fountains it gives you all records indexed as fountains or as water tricks.

Interestingly enough, those water tricks also demonstrate another handy feature of our thesauri. If you look at the record for water tricks you will notice we call them bedriegertjes in Dutch, but do not actually have an English label for them. Luckily, we have linked our concept of bedriegertjes with the concept of bedriegertjes in the Art & Architecture Thesaurus. This huge thesaurus tells us that bedriegertjes are known in English as water tricks or joke fountains.. It even tells us what they are called in German and Spanish. Opening us up to wealth of possible interactions with other systems.

In the end, theauri are a means. Not an end. Our prime concern is managing heritage, not building thesauri. But they do help us tremendously in defining what that heritage is, in searching through that heritage and in linking the heritage on our local level to the transnational level. If you want to know more about our thesauri, have a look at Mortier et al. [MVDM17], where we explain how we built them and provide you with some do’s and don’ts.