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#### 3.6.3 VOTable

VOTable is an XML-based format for tabular data endorsed by the International Virtual Observatory Alliance; 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, and it can be used for local table storage as well.

Any table which conforms to the VOTable 1.0, 1.1, 1.2, 1.3 or 1.4 specifications can be read. This includes all the defined cell data serializations; cell data may be included in-line as XML elements (TABLEDATA serialization), included/referenced as a FITS table (FITS serialization), or included/referenced as a raw binary stream (BINARY or BINARY2 serialization). The handler does not attempt to be fussy about input VOTable documents, and it will have a good go at reading VOTables which violate the standards in various ways.

Much, but not all, of the metadata contained in a VOTable document is retained when the table is read in. The attributes `unit`, `ucd`, `xtype` and `utype`, and the elements `COOSYS`, `TIMESYS` and `DESCRIPTION` attached to table columns or parameters, are read and may be used by the application as appropriate or examined by the user. However, information encoded in the hierarchical structure of the VOTable document, including `GROUP` structure, is not currently retained when a VOTable is read.

VOTable documents may contain more than one actual table (`TABLE` element). To specify a specific single table, the table position indicator is given by the zero-based index of the `TABLE` element in a breadth-first search. Here is an example VOTable document:

       <VOTABLE>
         <RESOURCE>
           <TABLE name="Star Catalogue"> ... </TABLE>
           <TABLE name="Galaxy Catalogue"> ... </TABLE>
         </RESOURCE>
       </VOTABLE>

If this is available in a file named "cats.xml" then the two tables could be named as "cats.xml#0" and "cats.xml#1" respectively.

Files in this format may contain multiple tables; depending on the context, either one or all tables will be read. Where only one table is required, either the first one in the file is used, or the required one can be specified after the "`#`" character at the end of the filename.

This format can be automatically identified by its content so you do not need to specify the format explicitly when reading VOTable tables, regardless of the filename.

The handler class for this format is `VOTableBuilder`.

To retrieve all of the tables from a given VOTable document, use one of the `makeStarTables` methods of StarTableFactory instead.

Much more detailed information about the VOTable I/O facilities, which can be used independently of the generic I/O described in this section, is given in Section 7.

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STIL - Starlink Tables Infrastructure Library
Starlink User Note252
STIL web page: http://www.starlink.ac.uk/stil/
Author email: m.b.taylor@bristol.ac.uk