Lab: Processing XML

Assigned

Wednesday, 13 April 2022

Summary

We consider some techniques for processing XML documents, including ways to extract information from XML documents and to build new XML documents from old.

Useful notation

'(tag (@ (name1 val1) (name2 val2) ...) element1 element2 ...)

A list-based representation of an XML/HTML element. The attribute section is optional. The elements are either strings or themselves XML/HTML elements.

"//tag"

An XPath pattern to search for elements with the given tag.

"//tag0/tag1"

An XPath pattern to search for elements with tag tag1 that appear directly under elements with tag tag0.

"//tag0//tag1"

An XPath pattern to search for elements with tag tag1 that appear anywhere under elements with tag tag0.

"//tag[1]"

An XPath pattern for the first instance of the tag within an enclosing element. (We also have similar "//tag[2]" and so on and so forth.)

"//tag[@class='name']"

An XPath pattern for all tags with the given class.

"//text()"

An XPath pattern for all of the text in a document.

"//tag[contains(text(),'string')]"

An XPath pattern for all instances of the tag that contain that string in their text.

Useful procedures

(file->xml fname)

Read an HTML or XML document and convert it to the list-based representation.

(xml->file xml fname)

Save the list-based representation of an HTML or XML document in a file.

(string->xml str)

Convert a string to the list-based representation.

(xml->string xml)

Convert the list-based representation to a string.

(sxpath-match pattern xml)

Search the xml document for matching patterns.

(sxpath-replace pattern xml proc)

Update any element matching the pattern by applying proc.

(sxpath-delete pattern xml)

Delete any element matching the pattern.

(sxpath-remove pattern xml)

Remove the tag in any element matching the pattern, moving any contents of the element up to the enclosing element.

Preparation

a. Have the traditional start-of-lab discussion. That is, introduce yourselves; discuss working strategies, strengths, and weakness; and review the reading.

b. You’ll need a variety of packages for this lab. Install the following packages in DrRacket using File -> Install Package….

• html-parsing
• html-writing
• sxml
• https://github.com/grinnell-cs/csc151www.git#main

c. Make a copy of excerpt.html, which you may recall from a recent lab.

d. Download the starter code for this lab.

• processing-xml.rkt

Acknowledgements

This lab is closely based on an earlier lab by Samuel A. Rebelsky. In Fall 2021, it was updated to add more details, to take the new “instructions in code form”, and to accommodate changes to our libraries.

The csc151www libraries to support these exercises on on the Racket SXML libraries, and on Neil Van Dyke’s html-parsing and html-writing libraries.