Metadata vs. Vocabularies

MetadataData about data. Metadata provides a context for research findings, ideally in a machine-readable format. It enables discovery of data via an electronic interface, and correct use and attribution of findings. Related Guide is used to describe the aspects of ‘something’. In the MMIMarine Metadata Interoperability community, the ‘something’ could be most anything related to the marine community, such as a data set, a marine oriented service, etc.

A metadata standardA set of documented rules which define the creation of metadata by providing a combination of terminology (vocabularies), syntactical rules, format rules, and other requirements. Metadata standards are approved, published and governed by a formal body or organization with broad community-based representation (international or national). Related Guide, also known as a content standardA list or hierarchy of required metadata elements to be included in the metadata description. Related Guide, is used to define the ‘containers’ for the metadata. The metadata standard is like a list of possibly important items for describing ‘something’. The metadata standard describes this all-encompassing list of containers. Since the list is all-encompassing, any specific container may or may not be of use for the particular thing being described.

A controlled vocabularyA managed list of terms. In the context of vocabularies, management typically includes careful selection of terms, maintenance of terms over time (i.e. addition, deprecation, modification), and presentation of the vocabulary in an accessible format. Related Guide is often used as the content for specific metadata containers. The controlled vocabulary, which is a managed list of acceptable terms, will predetermine all the possible ‘stuff’ that may be used in the ‘container’. If someone fills the container with text that is not included in the ‘stuff’, it will not be permitted to stay in the ‘container’. In this case, the controlled vocabulary could be defined internal or external to the metadata standard.

An example may help to distinguish the metadata containers from the terms in the controlled vocabulary. Suppose we are going to purchase a vehicle. In this example, the vehicle represents the ‘something’ we are going to describe. A hypothetical metadata standard to assist us in vehicle selection might consist of an all-encompassing list of important containers that describe any possible vehicle. These containers could include: model name, color, number of doors, number of passengers and whether or not there is a real spare tire (i.e., as opposed to the donut spare). Note that the descriptors in the all-encompassing list do not apply to every possible vehicle. For example, a motorcycle has no spare tire at all and thus the descriptor for ‘real spare’ doesn’t really apply.

Now consider the number of doors. In this case, the controlled vocabulary may be represented by the numbers 0, 2, 3, and 4. This controlled vocabulary allows for all passenger vehicles produced by all manufacturers. The zero case accounts for motorcycles; the two door case for two-door cars; and the three and four door case for the older and newer style vans (note, we are ignoring the gate or hatchback). No other valueMetadata values are the content connected to metadata labels in a metadata element. For example, if the metadata label is "date", the metadata value could be "May 13, 2007". Related Guide for the number of doors is possible in passenger vehicles.

In this example, the metadata standard represents the structure and metadata descriptors, while the controlled vocabulary is used to define the allowable content (e.g., the 0, 2, 3, 4 list) for the descriptors.