The Medical Subject Headings (MeSH) thesaurus is a controlled vocabulary widely used in biomedical knowledge systems, particularly for semantic indexing of scientific literature. As the MeSH hierarchy evolves through annual version updates, some new descriptors are introduced that were not previously available. This paper explores the conceptual provenance of these new descriptors. In particular, we investigate whether such new descriptors have been previously covered by older descriptors and what is their current relation to them. To this end, we propose a framework to categorize new descriptors based on their current relation to older descriptors. Based on the proposed classification scheme, we quantify, analyze, and present the different types of new descriptors introduced in MeSH during the last fifteen years. The results show that only about 25% of new MeSH descriptors correspond to new emerging concepts, whereas the rest were previously covered by one or more existing descriptors, either implicitly or explicitly. Most of them were covered by a single existing descriptor and they usually end up as descendants of it in the current hierarchy, gradually leading toward a more fine-grained MeSH vocabulary. These insights about the dynamics of the thesaurus are useful for the retrospective study of scientific articles annotated with MeSH, but could also be used to inform the policy of updating the thesaurus in the future.

医学主题词表 (MeSH) 词库是一种广泛用于生物医学知识系统的受控词汇表，特别是用于科学文献的语义索引。随着 MeSH 层次结构通过年度版本更新而演变，引入了一些以前不可用的新描述符。本文探讨了这些新描述符的概念来源。特别是，我们调查了这些新描述符之前是否已被旧描述符覆盖，以及它们当前与它们的关系是什么。为此，我们提出了一个框架，根据新描述符与旧描述符的当前关系对它们进行分类。基于提出的分类方案，我们量化、分析和展示了过去 15 年来 MeSH 中引入的不同类型的新描述符。结果表明，只有大约 25% 的新 MeSH 描述符对应于新出现的概念，而其余的先前已被一个或多个现有描述符隐式或明确地覆盖。它们中的大多数都被一个现有的描述符覆盖，并且它们通常最终成为当前层次结构中的后代，逐渐导致更细粒度的 MeSH 词汇表。这些关于叙词动态的见解对于用 MeSH 注释的科学文章的回顾性研究很有用，但也可用于为将来更新叙词的政策提供信息。它们中的大多数都被一个现有的描述符覆盖，并且它们通常最终成为当前层次结构中的后代，逐渐形成更细粒度的 MeSH 词汇表。这些关于叙词动态的见解对于用 MeSH 注释的科学文章的回顾性研究很有用，但也可用于为将来更新叙词的政策提供信息。它们中的大多数都被一个现有的描述符覆盖，并且它们通常最终成为当前层次结构中的后代，逐渐导致更细粒度的 MeSH 词汇表。这些关于叙词动态的见解对于用 MeSH 注释的科学文章的回顾性研究很有用，但也可用于为将来更新叙词的政策提供信息。