The Configuration File

This section describes the format of the ACL configuration file. When you refer to it you might find it useful to have to hand a copy of either simpleconfig.cfg or some other configuration file.

An ACL configuration file mediates the interaction between a client such as GAIA and a remote server. The configuration file comprises a list of one or more databases, giving details for each. Usually each `database' will be a simple astronomical catalogue. However, other alternatives are possible: archives, name servers, etc. Consequently, in this section the generic term `database' is used to denote each entry. Also, it is individual databases, not servers, which are listed in the configuration file: some servers might give access to more than one database. The details supplied for each database are things like: its URL, the type of queries supported, the name that will be used to describe it to users etc. The client reads the configuration file and the databases listed become the ones that it knows about.

By convention, configuration files have file-type `.cfg'. They are ASCII text files which may be created and modified with a text editor. Their basic syntax is as follows.

• Blank lines are ignored.

• Lines beginning with `#' are considered to be comments and are ignored.

• Lines ending with ` ${\tt\backslash}$' (backslash) are continued on the next line.

• The description for each database comprises several `keyword:value' pairs. Each keyword:value pair occupies a single line, unless continued over more than one line. The individual keywords are described in Section , below. Most are optional.

• The first keyword of each database entry must be serv_type.

• Subsequent keywords of each database entry can occur in any order.

• Unrecognised keywords are ignored (to permit future extensions).

• Many of the optional keywords correspond to facilities that are not supported by most databases.

• Some of the keywords require a list of values. All such lists have the same basic format as a Tcl¹ list: usually a list of words or strings enclosed in double-quotes (`"') and separated by one or more space characters. Alternatively, curly brackets (`{ }') may be used instead of double-quotes.

• If a keyword's value comprises more than one list then these lists are separated by a colon (`:').

• If a keyword's value includes a variable reference (see Section , below) then the variable is expressed in Tcl format: in practice it will start with a dollar character (` $').