Introduction to XQuery and eXist

Introduction to XQuery and eXist DSA

XSLT Tutorial Problems • Bad language : • No <xsl:annotation ..> ! • <xsd:annotation ..> for XML schema • Some XSLT engines tolerant of extra tags (permissive), others fail • Mime type table on our servers not set up • Should be an entry for file suffices • .xsl, .xslt • To set the MIME type • application/xml • Variations in server and browser configurations

Solution: server-side XSLT • Several XSLT engines • Xalan ( a free Java application) • SAXON • The Native XML Database eXists includes a command to apply a stylesheet to an XML file and get the results – uses Xalan

eXist Native XML Database • Open source • Wolfgang Meier is the chief architect • Written in Java • Deployable in different ways • Embedded in a Java application • Part of a Cocoon pipeline • As web application in Apache/Tomcat • With embedded Jetty HTTPserver (as on stocks) • Multiple Interfaces • REST – to Java servlet • SOAP • XML:RPC

Native XML database • Well-formed XML documents can be added to the database • They are stored in an efficient, searchable B+ tree structure • Documents (files) are organised into collections in a filestore • Non-XML resources (XQuery, CSS, JPEG ..), etc can be stored as binary

Executing an XQuery eXist: Server Client Browser User clicks link Get a.xql parameters servlet fetch a.xql parameters a.xql eXist DB html XQuery Engine render

Simple XQuery xquery version "1.0"; <table border='2'> <tr><th>Name</th><th>Address</th></tr> {for $w in doc('/db/whisky/data_raw.xml')/Whisky/Distillery return <tr><td>{data($w/Name)}</td> <td>{data($w/Address)}</td> </tr> } </table> addressList.xql

XQuery as HTML xQuery header xquery version "1.0"; <table border='2'> <tr><th>Name</th><th>Address</th></tr> {for $w in doc('/db/whisky/data_raw.xml')/Whisky/Distillery return <tr><td>{data($w/Name)}</td> <td>{data($w/Address)}</td> </tr> } </table> Xquery inside XML XPath expression to select nodes XQuery ‘variable’ addressList.xql

Executing an XQuery with XSLT eXist: Server Client Browser User clicks link Get a.xql parameters servlet fetch a.xql parameters a.xql eXist DB XQuery Engine .xml xslt html XSLT Engine render

Simplest XQuery -XSLT xquery version "1.0"; declare namespace transform = "http://exist-db.org/xquery/transform"; let $stylesheet := doc('/db/whisky/whisky.xslt'), $whiskySet := doc('/db/whisky/data_raw.xml') return transform:transform($whiskySet,$stylesheet,()) allWhiskys.xql

Simplest XQuery -XSLT Comma separator xquery version "1.0"; declare namespace transform = "http://exist-db.org/xquery/transform"; let $stylesheet := doc('/db/whisky/whisky.xslt'), $whiskySet := doc('/db/whisky/data_raw.xml') return transform:transform($whiskySet,$stylesheet,()) Retrieve this document a FLWOR expression namespace prefix allWhiskys.xql

XQuery with parameter xquery version=“1.0”; declare namespace transform = "http://exist-db.org/xquery/transform"; declare namespace request="http://exist-db.org/xquery/request"; let $whiskyType := request:request-parameter ("whiskyType",""), $stylesheet := doc('/db/whisky/whisky.xslt'), $whiskySet := <Whisky> {doc('/db/whisky/data_raw.xml')/Whisky/Distillery [WhiskyType = $whiskyType]} </Whisky> return transform:transform($whiskySet,$stylesheet,()) selectWhiskys.xql selectWhiskys.xql

XQuery with parameter xquery version=“1.0”; declare namespace transform = "http://exist-db.org/xquery/transform"; declare namespace request="http://exist-db.org/xquery/request"; let $whiskyType := request:request-parameter ("whiskyType",""), $stylesheet := doc('/db/whisky/whisky.xslt'), $whiskySet := <Whisky> {doc('/db/whisky/data_raw.xml')/Whisky/Distillery [WhiskyType = $whiskyType]} </Whisky> return transform:transform($whiskySet,$stylesheet,()) Get the value of the request parameter with this name Create an XML node XPath filter selectWhiskys.xql

XQuery is bi-lingualXML and XQuery • XML node (with a single root) <a> <b> h</b> </a> • XML Sequence of nodes (<a/>, <b/>, <c/>) • XQuery construct variable value $var function evaluation – see Function list concat($var,’.xm’) for loop FLWOR if-then-else if (cond) then expression else expression • Mixed expressions – need { } around XQuery to distinguish • <a> {if .. } {$x}</a> • if (cond) then <a> Fred </a> else ()

FLWOR expression • FLWOR for $x in sequence let $a := expression, $b := expression where condition order by $var return expression • Returns a Sequence of nodes • Compare with SQL select columns from tables where condition order by • Returns a Relation (table)

An XQuery sticky form • The script here has several shifts between XML to XQuery • Whole interface in one script • Equivalent to PHP + MySQL • XSLT revised to process a sequence of Distillery nodes into a sequence of HTML nodes.

Suggested Suffices • XQuery .xql • XSLT .xslt • XML .xml • CSS .css • JPEG .jpg

Tools for XQuery on stocks • Use a text editor (or Dreamweaver) • Use the admin interface with guest/guest login to create a directory and load all the files – including the XQuery files • To run a script, just click on the script in the directory listing – this will run the script (but with no parameters – you can add these in the Browser • This will show you the URL to execute it – you can then use this to link from any HTML outside the eXist database. • Use the test query interface to test small bits of XQuery and XPath

eXist on your own machine • Use the Java client to • load files • move, copy,rename files • edit files in situ (but no Save-as) • execute queries • backup

Introduction to XQuery and eXist