Xcerpt Tutorial - Chapter 1 (Hello World)

This document is (c)2003 Sebastian Schaffert and the Xcerpt Team.
Please contact schaffer@informatik.uni-muenchen.de on any questions.

It is a tradition for programming tutorials to begin with a "Hello World" example. The output of the following Xcerpt program is <p>Hello World</p>:

GOAL
    p { "Hello World" }
END
      

On this simple example, one can observe the following properties:

• Xcerpt uses a non-XML syntax. The rationale behind not using XML syntax is that the XML syntax does not support some special properties (explained below) and to emphasise that Xcerpt is not explicitly limited to XML data.
• An Xcerpt program consists of at least one "Goal". Goals special kinds of "Rules" and are the equivalent of the "main" function in many programming languages: If an Xcerpt program is executed, evaluation starts at the goals and the goals determine the output.

A goal has the following structure:

GOAL
  <construct part>
FROM
  <query part>
END
      

In a goal (and a rule), "cons" is wrapped around a term serving as construction pattern, and "query" is wrapped around a query specification (explained below). A "cons" part may be associated with an output resource, specifying where to write the results. If no output resource is provided, output is written to standard output. The following modified "Hello World"-example writes the document <p>Hello World</p> to the file "hello.html":

GOAL
  out {
    resource { "file:hello.html", "xml" },
    p { "Hello World" }
  }
END
      

Go to Chapter 2 to see the first real query.