Types of Vocabularies

As a managed list of acceptable terms, a controlled vocabulary helps to articulate, clarify, and narrow terminology. The managing body will generally choose to present the controlled vocabulary in a specific format, which is both documented and available for wider use. This documentation is of paramount importance for data managers who are looking to implement a given controlled vocabulary. It facilitates understanding of the structure of the controlled vocabulary and thus enables implementation. The documentation might provide additional information about each value, how the values relate to one another, and how to use a vocabulary. With this information, data managers can appropriately interpret the managed list of acceptable terms.

Categories of Controlled Vocabularies

There are three broad categories of controlled vocabularies: flat, multi-level and relational vocabularies. Within these three broad categories, there are a variety of specific types of controlled vocabularies - each of which serves a different function within different domains, and among a variety of metadata projects. Ultimately, all of these tools provide additional information about the set of terminology employed in a project. As such, they represent an invaluable resource for data gatherers, system managers, and metadata providers.

One word of caution: It is important to understand that the different types of controlled vocabularies rarely exist in a vacuum. In the "real metadata world", the differences between the various controlled vocabularies are often muddied- both intentionally and unintentionally. One controlled vocabulary might fit the definition of more than one type of controlled vocabulary. For example, an ontology might also have many of the characteristics of a dictionary. Because of these "gray" areas, the different types of controlled vocabularies are typically just called "vocabularies" or "controlled vocabularies". The vocabulary descriptions that follow are merely tools to help implement, utilize and understand a managed list of acceptable terms.

Types of Controlled Vocabularies

Controlled vocabularies are classified not only by their category (structure, characteristics), but by their type. So, for example, a controlled vocabulary that includes terms used to discover data can be distinguished from a controlled vocabulary that includes terms used to understand and thus use the data. Some controlled vocabularies are inherently designed for computer use (syntactic vocabularies), while others are created for human consumption (semantic vocabularies). It should be noted that sometimes a combination of "type" and "category" of vocabularies are used to refer to a specific controlled vocabulary.