Next Previous Up Contents
Next: CSV
Up: Output Formats
Previous: FITS

#### 4.1.2.2 VOTable

VOTable is an XML-based format for tabular data endorsed by the International Virtual Observatory Alliance and defined in the VOTable Recommendation. While the tabular data which can be encoded is by design close to what FITS allows, it provides for much richer encoding of structure and metadata. Most of the table data exchanged by VO services is in VOTable format, but it can be used for local table storage as well.

When a table is saved to VOTable format, a document conforming to the VOTable specification containing a single TABLE element within a single RESOURCE element is written. Where the table contains such information (often obtained by reading an input VOTable), column and table metadata will be written out as appropriate to the attributes `unit`, `ucd`, `xtype` and `utype`, and the elements `COOSYS`, `TIMESYS` and `DESCRIPTION` attached to table columns or parameters.

There are various ways that a VOTable can be written; by default the output serialization format is TABLEDATA and the VOTable format version is 1.4, or a value controlled by the `votable.version` system property. However, configuration options are available to adjust these defaults.

The handler behaviour may be modified by specifying one or more comma-separated name=value configuration options in parentheses after the handler name, e.g. "`votable(format=BINARY2,version=1.3)`". The following options are available:

`format = TABLEDATA|BINARY|BINARY2|FITS`
  Gives the serialization type (DATA element content) of output VOTables. (Default: `TABLEDATA`)
`version = 1.0|1.1|1.2|1.3|1.4|1.5|1.6`
  Gives the version of the VOTable format which will be used when writing the VOTable. Version `1.3` may alternatively be written as `V13` etc. (Default: `1.4`)
`inline = true|false`
  If true, STREAM elements are written base64-encoded within the body of the document, and if false they are written to a new external binary file whose name is derived from that of the output VOTable document. This is only applicable to BINARY, BINARY2 and FITS formats where output is not to a stream. (Default: `true`)
`compact = true|false|null`
  Controls whitespace formatting for TABLEDATA output, ignored for other formats. By default a decision will be taken dependent on table width. (Default: `null`)
`encoding = UTF-8|UTF-16|...`
  Specifies the XML encoding used in the output VOTable. The default value is UTF-8. Note that certain optimisations are in place for UTF-8 output which means that other encodings may be significantly slower. (Default: `UTF-8`)
`date = true|false`
  If true, the output file will contain a comment recording the current date; otherwise it is not included. (Default: `true`)

Multiple tables may be written to a single output file using this format.

If no output format is explicitly chosen, writing to a filename with the extension "`.vot`", "`.votable`" or "`.xml`" (case insensitive) will select `votable` format for output.

Next Previous Up Contents
Next: CSV
Up: Output Formats
Previous: FITS

TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk