Information on resource 'UCD Query'

The Unified Content Descriptor (UCD) is a formal vocabulary for astronomical data that is controlled by the International Virtual Observatory Alliance (IVOA). The vocabulary is restricted in order to avoid proliferation of terms and synonyms, and controlled in order to avoid ambiguities as far as possible. It is intended to be flexible, so that it is understandable to both humans and computers. UCDs describe astronomical quantities, and they are built by combining words from the controlled vocabulary.

A UCD does not define the units nor the name of a quantity, but rather "what sort of quantity is this?"; for example phys.temperature represents a temperature, without implying a particular unit.

It would be possible to describe astronomical data quantities in a natural language such as English or Hungarian or Uzbek; however, it would be very difficult to expect a machine to 'understand' it in any sense. At the opposite extreme, there is an attempt within the IVOA to describe astronomical data in terms of a hierarchical data model, so that there is a place for everything, and everything is in its place. The UCD vocabulary falls between these extremes, and is intended to be understandable to both humans and computers.

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