XML Mini-Tutorial

A schema for recipesThe following is a complete schema for the recipe example, written in the DSD schema language:... XML: XLink, XPointer, and XPathXLink, XPointer, and XPath are three

The recipe exampleSchema languages

A schema for recipesXLink, XPointer, and XPathPointing at recipes

XML-QLQuerying the recipesXSLT

A style sheet for recipesExercises

XML Mini-Tutorial

http://www.brics.dk/~mis/ITU/XML/ [18/09/2000 14:24:26]

What is XML?

XML is a framework for defining markup languages:

there is no fixed collection of markup tags;

XML is not a replacement for HTML:

HTML should ideally be just another XML language;

Rhubarb Cobbler made with bananas as the main sweetener

It was delicious Basicly it was

Combine all and use as cobbler, pie, or crisp

Related recipes: <a href="#GardenQuiche">Garden Quiche</a>

There are many problems with this approach:

the semantics is encoded into text formatting tags;

It would be much better to invent a special recipe markup language:

<recipe id="117" category="dessert">

<title>Rhubarb Cobbler</title>

<author><email>Maggie.Herrick@bbs.mhv.net</email></author> <date>Wed, 14 Jun 95</date>

This example illustrates:

the markup tags are chosen purely for logical structure;

A concrete view of XML

An XML document is a (Unicode) text with markup tags and other meta-information

Markup tags denote elements:

.<foo attr="val" > </foo>

| | | |

| | | a matching element end tag

| | the contents of the element

| an attribute with name attr and value val, values enclosed by ' or "

an element start tag with name foo

There is a short-hand notation for empty elements: <foo attr="val" />

Note: XML is case sensitive!!

An XML document must be well-formed:

start and end tags must match;

Special characters can be escaped using Unicode character references:

&#38; yields &;

The strange syntax is a legacy from SGML

The following service checks well-formedness of an XML document (given a full URL):

XML: a concrete view

http://www.brics.dk/~mis/ITU/XML/concrete.html [18/09/2000 14:24:32]

process clear

XML technologies

Just a notation for trees is not enough:

the real force of XML is generic languages and tools!

- grammars to define classes of documents;

linking between documents

- a generalization of HTML anchors and links;

addressing parts of documents

- it is not enough that only the author can place anchors;

We have some problems here:

the meaning of head and big depends on the context;

Do not be confused by the use of URI for namespaces:

they are not supposed to point to anything;

we rely on existing organizations that control domain names.

●

All XML technologies (are supposed to) respect namespaces

XML: namespaces

http://www.brics.dk/~mis/ITU/XML/namespaces.html (2 of 2) [18/09/2000 14:24:35]

The recipe example

Consider the following raw data describing some (Danish) recipes:

Schema languages

The syntax of a new XML language must be formalized:

this is similar to the formal syntax of a programming language;

A modern schema language:

is itself an XML language (and can be used to describe itself);

A schema for recipes

The following is a complete schema for the recipe example, written in the DSD schema language:

<AttributeDecl Name="kvantitet" Optional="no"/>

<AttributeDecl Name="tid" Optional="yes"/>

<AttributeDecl Name="navn" Optional="no"/>

<AttributeDecl Name="antal" Optional="yes">

<Else>

<Not><Attribute Name="enhed"/></Not> <Content IDRef="indhold"/>

XML: XLink, XPointer, and XPath

XLink, XPointer, and XPath are three related mechanisms:

they generalize the link mechanisms from HTML;

HTML links are just too simple:

an anchor must be placed at every link destination (problem with read-only documents)

- we want to express relative locations;

●

the link definition must be at the same location as the link source

- we want out-of-line links ("link databases");

●

only individual nodes can be linked to

- we want links to whole tree fragments;

●

a link always has one source and one destination

- we want links with multiple sources and destinations.

●

The XLink pointer model looks like this:

These technologies are not really supported by any browsers today

XML: XLink, XPointer, and XPath

http://www.brics.dk/~mis/ITU/XML/xpath.html [18/09/2000 14:24:38]

Pointing at recipes

The following simple XPath expressions point to parts of the XML recipe document:

//ingrediens[@navn="radiser i små tern"]/@antal

200

//ingrediens[@antal="100" and @enhed="g"]/@navn

flødeost med løg og urter

og saml hurtigt dejen Tryk den ud i en smurt springform (ca 22 cm

i diameter) Lad dejen gå halvt op ad formens side Stil den

tildækket i køleskabet i mindst 1 time Forbag bunden midt i ovnen

i 12 minutter ved 200 grader

XPath expressions navigate step by step through the XML tree

XML: pointing at recipes

http://www.brics.dk/~mis/ITU/XML/xpathrecipe.html [18/09/2000 14:24:39]

XML-QL is a query language for XML documents:

XML document can be seen as generalizations of database relations;

Relations are special, restricted cases of XML trees:

XML query languages are not released until 2001

XML: XML-QL

http://www.brics.dk/~mis/ITU/XML/xmlql.html [18/09/2000 14:24:40]

Querying the recipes

The following XML-QL queries extract information from the XML recipe document:

<titel>Hornfisk med radisesalat</titel>

<titel>Islagkage med chokolade</titel>

<titel>Rabarberdessert med jordbær</titel>

<?xml version="1.0"?>

<opskriftermedsukker>

<navn>Citrontærte</navn>

<navn>Islagkage med chokolade</navn>

<navn>Rabarberdessert med jordbær</navn>

<ingrediens navn="jordbær i skiver">

<ret>Rabarberdessert med jordbær</ret>

<ret>Rabarberdessert med jordbær</ret>

<ret>Islagkage med chokolade</ret>

<ret>Rabarberdessert med jordbær</ret>

<ret>Græsk farsbrød og agurkesalat</ret>

<ret>Græsk farsbrød og agurkesalat</ret>

<ret>Hornfisk med radisesalat</ret>

<ret>Laksemousse</ret>

</ingrediens>

<ingrediens navn="knust fed hvidløg">

<ret>Græsk farsbrød og agurkesalat</ret> </ingrediens>

<ingrediens navn="groft salt">

<ingrediens navn="Feta ost 45+">

<ret>Græsk farsbrød og agurkesalat</ret> </ingrediens>

<ingrediens navn="frisk, rød chilipeber"> <ret>Filokurve med tigerrejer</ret>

</ingrediens>

<ingrediens navn="tørret basilikum">

<ret>Smørrebrød med flødeost og tomat</ret> </ingrediens>

<ingrediens navn="lille hakket zittauerløg"> <ret>Græsk farsbrød og agurkesalat</ret> </ingrediens>

<ingrediens navn="smør">

<ret>Filokurve med tigerrejer</ret>

<ret>Græsk farsbrød og agurkesalat</ret> </ingrediens>

<ingrediens navn="hakket hvidløgsfed">

<ret>Filokurve med tigerrejer</ret>

</ingrediens>

<ingrediens navn="creme fraiche">

<ret>Filokurve med tigerrejer</ret>

<ret>Islagkage med chokolade</ret>

</ingrediens>

<ingrediens navn="smeltet overtrækschokolade">

<ret>Islagkage med chokolade</ret>

</ingrediens>

<ingrediens navn="agurk">

<ret>Filokurve med tigerrejer</ret>

</ingrediens>

<ingrediens navn="udbenet hornfisk">

<ret>Hornfisk med radisesalat</ret>

<ingrediens navn="frisk, klippet purløg">

<ret>Hornfisk med radisesalat</ret>

</ingrediens>

<ingrediens navn="jordbærskiver">

<ret>Rabarberdessert med jordbær</ret>

</ingrediens>

<ingrediens navn="limefrugt i halve skiver">

<ret>Filokurve med tigerrejer</ret>

</ingrediens>

<ingrediens navn="creme fraiche 18%">

<ret>Hornfisk med radisesalat</ret>

</ingrediens>

<ingrediens navn="friske, hakkede citronmelisseblade">

<ret>Filokurve med tigerrejer</ret>

<ingrediens navn="agurk i små tern">

<ret>Hornfisk med radisesalat</ret>

</ingrediens>

<ingrediens navn="cherrytomater i skiver">

<ret>Smørrebrød med flødeost og tomat</ret>

</ingrediens>

<ingrediens navn="magert, hakket svinekød">

<ret>Græsk farsbrød og agurkesalat</ret>

</ingrediens>

<ingrediens navn="flødeost med løg og urter">

<ret>Smørrebrød med flødeost og tomat</ret>

XML: querying the recipes

http://www.brics.dk/~mis/ITU/XML/xmlqlrecipe.html (5 of 7) [18/09/2000 14:24:42]

<ingrediens navn="hakket lammekød">

<ret>Græsk farsbrød og agurkesalat</ret>

<ingrediens navn="parboiled ris">

<ret>Græsk farsbrød og agurkesalat</ret>

</ingrediens>

<ingrediens navn="blødt smør i mindre stykker"> <ret>Citrontærte</ret>

</ingrediens>

<ingrediens navn="iskold piskefløde">

<ret>Rabarberdessert med jordbær</ret>

<ingrediens navn="radiser i små tern"> <ret>Hornfisk med radisesalat</ret>

An XSLT style sheets transforms an XML document into another:

if the target language is XHTML, then this is similar to a CSS style sheet;

There is little support for XSLT style sheets yet:

Netscape 4 does nothing;

http://www.brics.dk/~mis/ITU/XML/xslt.html [18/09/2000 14:24:43]

http://www.brics.dk/~mis/ITU/XML/karoline.xml process clear

A style sheet for recipes

The following XSLT style sheet illustrates many features (the two namespaces are in different colors):

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns="http://www.w3.org/1999/xhtml">

<xsl:if test="@alkohol">

<td align="right"><xsl:value-of select="@alkohol"/>%</td> </xsl:if>

Add the necessary HTML to the following style sheet:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns="http://www.w3.org/1999/xhtml">

</html>

4

XML: exercises

http://www.brics.dk/~mis/ITU/XML/exercises.html [18/09/2000 14:24:45]