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Parsing XML into Data Structures

Problem

You want a list that corresponds to the structure and content of an XML file.

Solution

For example you have this example:

<?xml version="1.0" standalone="yes"?>
<rhythmdb version="1.0">
  <entry type="song">
    <title>Never Let Me Down Again</title>
    <genre>Pop/Rock</genre>
    <artist>Depeche Mode</artist>
    <album>Music For The Masses</album>
    <track-number>1</track-number>
    <duration>287</duration>
    <file-size>6533368</file-size>
    <location>file:///home/hector/ogg/depeche_mode/music_for_the_masses/never_let_me_down_again.ogg</location>
    <mtime>1079831032</mtime>
    <play-count>1</play-count>
    <last-played>1083552958</last-played>
    <mimetype></mimetype>
  </entry>
</rhythmdb>

We will use SSAX library to parse this XML file in to a SXML abstract syntax tree. In specific we will use the ssax:xml->sxml function that takes a stream and a list of (user-prefix . uri-string) that assigns user prefixes to certain namespaces identified by particular URIs. In this example the file is a config named rhythmdb.xml and the XML namespace is the default so we put the empty list.

(require (lib "ssax.ss" "ssax"))
(ssax:xml->sxml (open-input-file "rhythmdb.xml") '())

This outputs a SXML abstract syntax tree that for all situations can be handled like a list:

> (ssax:xml->sxml (open-input-file "rhythmdb.xml") '())
(|*TOP*|
 (|*PI*| xml "version=\"1.0\" standalone=\"yes\"")
 (rhythmdb
   (@ (version "1.0"))
   (entry
    (@ (type "song"))
    (title "Never Let Me Down Again")
    (genre "Pop/Rock")
    (artist "Depeche Mode")
    (album "Music For The Masses")
    (track-number "1")
    (duration "287")
    (file-size "6533368")
    (location "file:///home/hector/ogg/depeche_mode/music_for_the_masses/never_let_me_down_again.ogg")
    (mtime "1079831032")
    (play-count "1")
    (last-played "1083552958")
    (mimetype))))

If we want to parse the rhythmdb.xml from a string, we use:

(require (lib "ssax.ss" "ssax"))
(ssax:xml->sxml (open-input-string rhythmdb-string) '())

And the output is the same from parsing the rhythmd.xml file.

Discussion

Discussion here

See Also

• SSAX/SXML Home Page

Comments about this recipe

Shortening the location element to about 40 characters would make Web and print layout easier.

-- NeilVanDyke - 20 May 2004

Contributors

-- HectorEGomezMorales - 19 May 2004