The Tab-Separated Table Format

This section gives a brief description of the tab-separated table (TST) format. ACL servers should return the list of selected objects in this format. Various packages, including GAIA, CURSA and Starbase can also read local files containing catalogues in this format. There are alternative descriptions of it in SUN/214[4], the Starbase FAQ and the Astronomical Catalogue Library User Manual[2].

TST format files are text files. They are usually generated by a remote server in response to a query from a local client. However, they could equally well be local files created with a text editor. Figure

shows a simple example of a tab-separated table. This example is available as file:

**Figure:** A simple tab-separated table. Note that in a tab-separated table the list of column names, sequences of dashes and fields in the table are separated by tab characters. In this figure tab characters are indicated by ``<tab>`'. (Note that the first column, `Id`, is an object name and hence its units are left blank. Thus, the CURSA-specific `column-units:` is separated from the following `<tab>` character by only one or more spaces; see Section for details of the CURSA extensions.)
$\begin{figure}\par \begin{verbatim}Simple TST example; stellar photometry cata... ...11<tab> -0.47 ...\end{verbatim} \par \begin{quote}\end{quote}\par \end{figure}$

The description of the table and the table of values occupy the same file and the description occurs at the start of the file. Most of the description shown in Figure

is optional.

The first line of the description is a title. Lines beginning with a `#' are comments which are ignored.

Parameter definitions start with the parameter name, and a colon (`:') is appended to the end of the name to identify it as such. The rest of the line contains the parameter value. The name and value are the only information stored for each parameter. The example contains two parameters: EQUINOX and EPOCH.

Any remaining lines in the description (apart from the last two, which immediately precede the table of values) are free text.

The only mandatory items in the description are the two lines immediately before the table of values. The first of these lines is the list of column names. Each name is separated by a single tab character (ASCII code nine; strictly speaking the horizontal tab). In the figure tab characters are shown as `<tab>'; obviously a real tab-separated table would contain actual tab characters instead. The name is the only mandatory information stored for each column. The TST format places few restrictions on the column names: they can contain spaces, special and punctuation characters etc. However, it is usually a prudent precaution to restrict column names to contain only alphanumeric and underscore (`_') characters and to make the first character alphabetic. If these precautions are observed then fewer problems are likely to occur if the table is subsequently converted to another format or read by a variety of different clients. Remember that if you are writing a server which returns a TST table via the Internet then you do not know which client will be used to access it.

The line immediately after the list of column names indicates the end of the description and the start of the table. It consists solely of dashes and tab characters. By convention there are as many sequences of dashes as there are column names, each sequence is separated by a single tab character and each has the same number of dashes as there are characters in the corresponding column name.

In the table of values each row occupies a single line. Individual fields are separated by a single tab character. The fields occur in the same order as the corresponding column names.