Playground page for the XML Course

For practical exercises, the XML software will be installed in the IFI CIP Pool.

Students @GOE: IFI pool account application via the user interface at the assigned computers in the pool,
Students @CLZ: IFI pool account application via mail to Gunnar Krull.

XML examples
XML tools
XHTML
XPath
XQuery
XSLT
XLink
XML schema
SQL/XML
RDF

XML Examples

The small "books" example (books.xml, books.dtd) of the lecture is available in the directory

/afs/informatik.uni-goettingen.de/course/xml-lecture/XML-DTD

Data-centric XML: The Mondial XML database

In the course, a nested XML version of the Mondial database is used.

XML instance "mondial.xml"
- excerpt: europe "mondial-europe.xml"
DTD "mondial.dtd"
XML Schema "mondial.xsd"

You find also all Mondial XML files in the directory /afs/informatik.uni-goettingen.de/course/xml-lecture/Mondial

Text-oriented XML: Shakespeare's Plays

A more text-oriented example uses Shakespeare's plays by John Bosak.
The files (XML and DTD) are installed at /afs/informatik.uni-goettingen.de/course/xml-lecture/Shakespeare/ .

Mixed Text- and Database-oriented XML: DBIS publication list

The following files are available in the directory

/afs/informatik.uni-goettingen.de/course/xml-lecture/XML-DTD

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XML Tools and Links

Browsing, editing

Browsing: Use mozilla/firefox: for looking at XML instances.
XML instances that are not HTML/XHTML are presented by their XML structure - then you can click subtrees to open or close.
Editing: kxmleditor.

Validation, Navigation, Exploration

xmllint
- xmllint -loaddtd -valid -noout filename validates a given file against the DTD given in its DocTypeDecl.
- xmllint can also be used for actually navigating inside an XML instance:
  - call xmllint -loaddtd -shell filename.
    Then, the following commands are allowed:
  - validate does a (somewhat sloppy) validation.
  - pwd gives the current path.
  - cat outputs the current node in ASCII.
  - cat xpath-expr ouputs the result of evaluating the xpath-expr wrt. the current node.
  - cd xpath-expr navigates to the node addressed by xpath-expr bezeichneten Knoten. xpath-expr must result in a single node.
  - du xpath-expr lists the contents of the current node.
  - dir xpath-expr gives nodetype and atributes.
  - try the following example session:
```
          xmllint -shell mondial-europe-2.0.xml
          pwd
          cat //country
          cat //country/name
          cat //country[name="Germany"]
          cd //country[name="Germany"]
          pwd
          cd province[9]
          du
          cat name
          dir
          cd id('cty-Germany-Hannover')
          cat
          pwd
```
- with saxon (see Section on XQuery) call saxonXQ -dtd:on -s:filename xpath/xquery expression filename.
```
    saxonXQ -dtd:on -s:mondial.xml bla.xq
    
```

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XHTML

XHTML 1.0/HTML 4.01 is described at http://www.w3.org/TR/html/.
DTDs of XHTML 1.0 for downloading can be found here.

Usually, the DTD on the W3C server is referenced by

    <!DOCTYPE html PUBLIC
       "-//W3C//DTD XHTML 1.0 Strict//EN"
       "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Note that this DTD associates a namespace with XHTML documents via

        <!ELEMENT html (head, body)>
        <!ATTLIST html
          xmlns       %URI;          #FIXED 'http://www.w3.org/1999/xhtml'
        >

(see comments on querying XHTML below for the consequences of this).

The W3C provides a validator that checks the validity of HTML/XHTML documents and reports problems.
Here is an example XHTML document (that validated in early 2002).
HTML documents can be transformed (more or less ...) to XHTML by tidy html-filename > out-filename

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XPath

Parts of XPath are also supported by xmllint (see above).
XPath queries can be executed using several tools:

(as a subset of XQuery) using the XQuery-Demo WebService (against publicly available XML instances); see below for XQuery, or
using saxonXQ (again, as a subset of XQuery, for more information, see next section).
Here, the document must be given explicitly by doc('filename'); it is possible to access either documents in the local filesystem or anywhere on the Web.
Example for usage of saxonXQ:
```
     saxonXQ "{doc('/afs/informatik.uni-goettingen.de/course/xml-lecture/Mondial/mondial.xml')//country/name}"
     saxonXQ "{doc('http://www.dbis.informatik.uni-goettingen.de/Mondial/mondial.xml')//country/name}"
```

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XQuery

The W3C provides information about XQuery; the bottom of that page also lists numerous implementations. Some of them are available:

the saxon lightweight tool:
The following aliases should be set in the file .bashrc:
```
alias saxonXQ='java -cp /afs/informatik.uni-goettingen.de/group/dbis/public/saxon/saxon8.jar net.sf.saxon.Query'
```
```
alias saxonXSL='java -cp /afs/informatik.uni-goettingen.de/group/dbis/public/saxon/saxon8.jar net.sf.saxon.Transform' 
```
Call saxonXQ filename.xq to execute an XQuery (or XPath query) from a file. The query in filename.xq must address a document by using the
doc('filename.xml or url') function.
Here, filename.xml is a name of a file in the local file system, saxonXQ also accepts urls for addressing documents from the web.
In order to call saxonXQ for a local file, additionally the option "-s" can be used:
```
saxonXQ -s /afs/informatik.uni-goettingen.de/course/xml-lecture/Mondial/mondial.xml filename.xq
```
Thus, it is not necessary to specify the document in the query file. This can also be specified as an alias:
```
alias saxonXQMondial='saxonXQ -s /afs/informatik.uni-goettingen.de/course/xml-lecture/Mondial/mondial.xml'
```
Download: Download Saxon, unpack it, set CLASSPATH accordingly, set aliases for saxon-XQuery and saxon-XSL accordingly.
The XQuery-Demo WebService. This WebService also uses Saxon internally.

The WebService is also available for local installations at
/afs/informatik.uni-goettingen.de/course/xml-lecture/XML-Tools/xquery-demo.war
It can be used with any standard web application server, e.g. tomcat.

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XSLT Stylesheets

The main use for XSLT stylesheets is the transformation fom XML to XML or to HTML (see also below).

Overview of XSLT Processors under debian linux: http://www.togaware.com/linux/survivor/XSLT_Processors.html
note that there are versions XSLT 1.0 and XSLT 2.0 (that have to be given in the stylesheet); from the processors below, currently only saxon supports XSLT 2.0:
saxon (supports XSLT 2.0):
call saxonXSL xml-file stylesheet.xsl
In order to install it yourself: download Saxon, unpack it, set CLASSPATH accordingly, set aliases for saxon-XQuery and saxon-XSL accordingly.
xalan (implements XPath/XSLT 1.0):
xalan -xsl stylesheet.xsl -in xml-input
xsltproc (belongs to the XSLT library for Gnome):
xsltproc stylesheet.xsl xml-input
xsltproc −−debug stylesheet.xsl xml-input produces a "sax-style" depth-first traversal of the input tree.

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Transformation Stylesheets

if a stylesheet is given in the document header, most browsers do not show the XML source, but directly apply the stylesheet and show the result:
mondial-with-stylesheet.xml is processed by mondial-simple.xsl that shows a table of the countries. If you execute "view page source" in your browser, you see the original XML file.
redirected-input.xsl is a stylesheet that gets its input from another file. Try this out by viewing dummy.xml in your browser: viewing this file starts redirected-input.xsl that in course states a query against mondial-europe.xml.
other example stylesheets can be found in /afs/informatik.uni-goettingen.de/course/xml-lecture/XSLT:
- orgs-and-members.xsl (XML to HTML)
- redirected-output.xsl (generates two new XML instances from one)

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XMLSchema

Example: mondial.xsd, can also be found here:

/afs/informatik.uni-goettingen.de/course/xml-lecture/XMLSchema/mondial.xsd

SQC (XML Schema Quality Checker) checks the quality of a schema (i.e. validates it against the XML Schema Specification) (i.e., it does not validate a document against an XML Schema).
- move to cd /afs/informatik.uni-goettingen.de/course/xml-lecture/XML-Tools/SQC and then call ./SQC.sh any-xsd-filename.xsd.
An online validator for validating a given XML instance against a schema is available at http://www.w3.org/2001/03/webdata/xsv.
Give first the url of an XML file and then the url of the XSD file (separated by a blank).
Note: this web interface seems to cache the files, changes are sometimes only effective if the filename changes.
xmllint can be used for XML Schema validation:
xmllint -noout -schema <schemafilename> <file.xml>

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SQL/XML under Oracle

There is an Oracle instance accessible from the CIP-Pool. Use the global alias command sqlap34 for logging into a dummy account (one account for all).
Please do not change the mondial tables (otherwise, start @consult and re-create the respective table). The user is allowed to create tables and views - please identify everything you create by your name (e.g. CREATE TABLE MAY_COUNTRY (...)) and delete it if you don't need it any more.
an online documentation can be found here.

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RDF/OWL

The W3C RDF Validator validates and visualizes RDF documents (given in RDF/XML format).
a collection of OWL ontologies

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Table of contents

Data-centric XML: The Mondial XML database

Text-oriented XML: Shakespeare's Plays

Mixed Text- and Database-oriented XML: DBIS publication list

Browsing, editing

Validation, Navigation, Exploration

Transformation Stylesheets