Playground page for the XML Course

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/
Here is an example.

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
  - 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
```

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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 eXist-WebInterface (against locally stored 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}"
```
embedded into an XSLT stylesheet by using any xslt processor (see below under "XSLT").

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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 eXist database system:
- Web interface at http://ap34.ifi.informatik.uni-goettingen.de:8081/exist/xquery/xquery.xq
- XML documents in the database can also be accessed by HTTP as, e.g.,
  http://ap34.ifi.informatik.uni-goettingen.de:8081/exist/xmldb/db/xmlcourse/mondial.xml
  (here: mondial.xml in the db collection)
- Mondial is also an "official" example at the eXist pages, they also provide a Web interface at http://demo.exist-db.org/exist/xquery/xquery.xq.
In eXist, documents are addressed by doc('filename'). E.g. doc('/db/xmlcourse/mondial.xml')/mondial/country
Here, filename has to be the name of a file stored in the eXist database.
The following douments are currently stored locally:
- /db/xmlcourse/mondial.xml: mondial.xml
- /db/xmlcourse/hamlet.xml: hamlet.xml
- /db/xmlcourse/publications.xml: the DBIS publications database
- /db/xmlcourse/xlink.htm: the XLink paper in XHTML format
  Note that for querying it, the XHTML namespace must be declared:
```
          declare namespace xhtml = "http://www.w3.org/1999/xhtml"; 
           doc('/db/xlink.htm')//xhtml:img
```
the saxon lightweight tool:
First, 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. Declaration of namespaces in filename.xq is done in the same way as for eXist.
GalaX:
GalaX is implemented in OCaml. Invoke it from the commandline typing galax filename.xq. Address the document to be queried in a similar way as with saxon. Documentation and some examples can be found at /usr/local/share/Galax/.

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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: http://www.togaware.com/linux/survivor/XSLT_Processors.html
using xalan (implements XPath-1.0):
xalan -xsl stylesheet.xsl -in xml-input
using 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.
using saxon:
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.

A first application is to embed queries into a simple stylesheet (available in /afs/informatik.uni-goettingen.de/course/xml-lecture/XPath):

for executing these examples, cd /afs/informatik.uni-goettingen.de/course/xml-lecture/XPath or copy all files (including xml and dtds) into your directory.
For experimenting with different queries, copy the file and change line 13 in the .xsl file.

queries against Mondial:

/afs/informatik.uni-goettingen.de/course/xml-lecture/XPath/mondial-queries.xsl

queries against hamlet.xml (belongs to the Shakespeare collection):

/afs/informatik.uni-goettingen.de/course/xml-lecture/XPath/hamlet-queries.xsl

queries against the XHTML paper, these queries illustrates the use of namespaces. Note that the xsl:stylesheet element declares the xhtml namespace:
```
/afs/informatik.uni-goettingen.de/course/xml-lecture/XPath/xlinkpaper-queries.xsl
```
a generic frame for stating queries against arbitrary documents using XPath's document(...) function
call it by e.g. xalan -xsl web-queries.xsl -in web-queries.xsl since it ignores the -in option. Note the use of a namespace when querying XHTML pages:
```
/afs/informatik.uni-goettingen.de/course/xml-lecture/XPath/web-queries.xsl
```

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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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XLink

XLink serves for interlinking XML resources.

Browsing: Amaya is an open-source browser that understands XLink, RDF etc (not yet installed).
Databases: a distributed version of Mondial can be found at http://user.informatik.uni-goettingen.de/~may/Mondial#XLinked
It is also available in the directory
```
/afs/informatik.uni-goettingen.de/course/xml-lecture/Mondial/Mondial-Distributed
```
.

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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>
(although it seems to have internal problems)
Another XML Schema validator is available at http://apps.gotdotnet.com/xmltools/xsdvalidator/Default.aspx (somewhat weird behavior - seems to require a namespace declaration).

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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.
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