votable

VOTable is an XML-based standard defined by the International Virtual Observatory Alliance (IVOA) for the interchange of tabular data in astronomy. It is designed to be self-describing, carrying rich metadata about each column, including human-readable names, units, data types, and semantic descriptors such as Unified Content Descriptors (UCDs) and UTypes that link columns to data models. This makes it possible for different software to interpret and integrate catalogues, time series, or other tabular data without external references.

A VOTable document consists of a VOTABLE element that contains one or more RESOURCE elements, which in turn contain TABLE elements describing the columns and the data. Within a TABLE, FIELD elements define columns, and PARAM, GROUP, and LINK elements provide additional metadata and relationships. The actual data can be stored in the DATA element using one of several encodings: TABLEDATA (an inline XML representation of rows and cells), BINARY, or BINARY2. The TABLEDATA encoding yields human-readable XML, while BINARY and BINARY2 offer more compact and efficient representations for large tables.

Fields specify attributes such as name, datatype, and arraysize, and may also include unit, ucd, and utype to convey scientific meaning. Data rows are represented as TR elements with TD cells under TABLEDATA, or as binary blocks in the other encodings. VOTable has become widely used in the Virtual Observatory to exchange catalogs, survey results, and time-series data, and is supported by common VO tools and services such as TOPCAT, Aladin, and many data centers.