Analyzing the Evolution of Linked Vocabularies

Reusing terms results in a Network of Linked vOcabularies (NeLO), where the nodes are the vocabularies that use at least one term from some other vocabulary and thus depend on each other. These dependencies become a problem when vocabularies in the network change, e. g., when terms are deprecated or deleted. In these cases, all dependent vocabularies in the network need to be updated. So far, there has been no study that analyzes vocabulary changes in NeLO over time. To address this shortcoming, we compute the state of NeLO from the available versions of the vocabularies over 17 years. We analyze static parameters of NeLO such as its size, density, average degree, and the most important vocabularies at certain points in time. We further investigate how NeLO changes over time. Specifically, we measure the impact of a change in one vocabulary to others, how the reuse of terms changes, and the importance of vocabularies changes. Our analyses provide for the first time in-depth insights into the structure and evolution of NeLO. This study helps ontology engineers to identify shortcomings of the data modeling and to assess the dependencies implied with reusing a specific vocabulary.