Introduction to XQuery and eXist DSA

XSLT Tutorial Problems Bad language : – No ! – 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 DB a.xql XQuery Engine parameters html Client Browser eXist: Server Get a.xql parameters servlet fetch a.xql render User clicks link

Simple XQuery xquery version "1.0"; Name Address {for $w in doc('/db/whisky/data_raw.xml')/Whisky/Distillery return {data($w/Name)} {data($w/Address)} } addressList.xql

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

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

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

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

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

XQuery is bi-lingual XML and XQuery XML node (with a single root) h XML Sequence of nodes (,, ) 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 – {if.. } {$x} –if (cond) then Fred 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