eXtensible Markup Language

Jesús Ibáñez, Toni Navarrete, Josep Blat

Universitat Pompeu Fabra

eXtensible Markup Language

• New Internet mark-up metalanguage

• Previously: SGML, HTML, DHTML’s

• Extensibility, structure and validation

• SGML adaptation for WWW

eXtensible Markup Language

• Defined as standard by W3C (Generic SGML Editorial Review Board - XML Working Group)

• XML != HTML++ ; XML == SGML--

• XML, DTD (Document Type Definition) and XSL (eXtensible Style Language)

Main Characteristics

Describing semantically document content Uncoupling semantic description from

presentation Allowing each user community to define its

own labels, for instance: <PRICE>, <AUTHOR>, <SECTION>, <DATE>, <IMPORTANCE

LEVEL="Expert">

XML Example (without DTD)

<?XML version="1.0" standalone="yes"?>

<conversation>

<greeting>Hello world!</greeting>

<answer>Stop it, I’m getting off!</answer>

</conversation>

Example with DTD (1)

<!DOCTYPE Book[

<!ELEMENT Book(Title, Author, Date, ISBN, Publisher)

<!ELEMENT Title(#PCDATA)>

<!ELEMENT Author(#PCDATA)>

<!ELEMENT Date(#PCDATA)>

<!ELEMENT ISBN(#PCDATA)>

<!ELEMENT Publisher(#PCDATA)>

]>

Example with DTD (2)<?xml version="1.0"? standalone=“no”><!DOCTYPE Book SYSTEM

"file://localhost/xml-course/xsl/Book.dtd"><Book> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>July, 1998</Date> <ISBN>94303-12021-43892</ISBN> <Publisher>McMillan Publishing</Publisher></Book>

DTDs

• Allow to create new sets of labels• Examples:

– <!ELEMENT Title (#PCDATA)>– <!ELEMENT Disk (Disk)+> (1 or more)– <!ELEMENT Book (Book)*> (0 or more)– ? (0 or 1) , (sequence) | (option)– Attributes:

• <!ATTLIST ARTICLE DATE CDATA>(CDATA means Character Data)

• <!ATTLIST PERSON GENDER (male | female) #IMPLIED>(optional)

• <!ATTLIST PERSON GENDER (male | female) “male” #REQUIRED>(required)

DTDs

<!DOCTYPE Discography[

<!ELEMENT Discography (disk)*>

<!ELEMENT Disk (Title, Group, Song*)>

<!ELEMENT Title(#PCDATA)>

<!ELEMENT Group(#PCDATA)>

<!ELEMENT Song (titleS, Duration>

<!ELEMENT titleS(#PCDATA)>

<!ELEMENT Duration(#PCDATA)>

]>

DTDs< Discography>

< Disk>< Title>Brother in arms</ Title>< Group>Dire Straits</ Group>< Song>

< titleS>Money for nothing</ titleS>< Duration>5:20</ Duration>

</ Song>< Song>

<titleS>So far away</titleS><duration>4:10</duration>

</ Song>...

</Disk><Disk>

<Title>On every street</Title><Group>Dire Straits</Group><Song>...

</Disk></Discography>

DTDs

<!DOCTYPE publications[

<!ELEMENT publications (disk | book)*>

<!ELEMENT book ... >

<!ELEMENT disk ... >

]>

DTDs<publications>

<disk><titledisk>Brother in arms</titledisk><group>Dire Straits</group><song>

<titleS>Money for nothing</titleS><duration>5:20</duration>

</song>...

</disc><book>

<titlebook>Cien años de soledad</titlebook><writer>Gabriel García Márquez</writer>...

</book><book>

<titlebook>La ciudad de los prodigios</titlebook><writer>Eduardo Mendoza</writer>...

</book></publications>

DTDs

<?xml version="1.0"?><!DOCTYPE file [

<!ELEMENT file (name+, surname+, address+, picture?)><!ELEMENT name (#PCDATA)><!ATTLIST name sex (male|female) #IMPLIED><!ELEMENT surname (#PCDATA)><!ELEMENT address (#PCDATA)><!ELEMENT picture EMPTY>

]>

<file><name sex=“male”>Toni</name><surname>Navarrete</surname><surname>Terrasa</surname><address>Rambla 32</address>

</file>

Well formed vs valid

• Valid XML: the content conforms to the rules of the associated DTD. – Completeness, good format and attribute values

of the XML data is ensured.

• Well formed: adjusted to XML syntax– An XML document without DTD can be well

formed but, of course, cannot be valid.

XML Schemata

• XML Schemata to define the structure of XML documents (same as DTDs)

• BUT in XML syntax. Advantage: same parser to validate, tools for dynamic creation

• Use of Namespaces• Improved data type definition (41 instead of 10, plus

user-defined)• Object orientation allows new types by extension or

restriction of previous ones• Validation (a document wrt a scheme, a scheme wrt

scheme of schemes)

Schema definition

• An XML document whose root is “schema” and within it elements and attributes are defined:<?xml version="1.0“?><schema>

... elements and attributes definition</schema>

• element definition<element name=“name of the element”

type=“type of the element”[options...]

>

Simple types of elements– string: characters chain

– boolean (false, 0, true, 1)

– float (32 bits)

– double (64 bits)

– decimal (integer)

– timeDuration

– recurringDuration (several subtypes)

– binary

– uriReference (Uniform Resource Indicator)

And derived from these basic ones

Data type structure

Example

<?xml version="1.0“ encoding="ISO-8859-1“?><bookshop>

<book isbn="84-111-1111-1"><title>El Quijote</ title><author>Miguel de Cervantes</author><publisher>Plaza y Janés</publisher><character>Don Quijote</character><character>Sancho Panza</character><character>Dulcinea</character><character>Rocinante</character></book><book isbn="84-222-2222-2"> <title>La ciudad de los prodigios</ title><author>Eduardo Mendoza</author><publisher>Seix-Barral</publisher><character>Onofre Boubila</character><character>Efren Castells</character></book><book isbn="84-333-3333-3"><title>Cien años de soledad</title><author>Gabriel García Márquez</author><publisher>Planeta</publisher><character>Aureliano Buendía</character></bookshop>

XML document previous to schema definition

Building blocks: simple elements and cardinality

• Simple elements:<element name=“title" type="string" /><element name="author" type="string" /><element name=“publisher" type="string" /><element name=“character"

minOccurs="0" maxOccurs="unbounded" />

• A DTD would be like:<!ELEMENT title (#PCDATA)>

• In the cardinality definition we replace the DTD symbols ?, *, +

Building blocks: Complex types• The element book is composite, thus we define it as a

complex type:<element name=“book">

<complexType><sequence>

<element name=“title" type="string" /><element name="author" type="string" /><element name=“publisher" type="string" /><element name=“character" minOccurs="0"

maxOccurs="unbounded" /></sequence>

</complexType></element>

Alternative: naming complex types

• We could also define a complex type with a name:<element name=“book” type=“Booktype” />

<complexType name=“Booktype”><element name=“title" type="string" /><element name="author" type="string" /><element name=“publisher" type="string" /><element name=“character" minOccurs="0"

maxOccurs="unbounded" /></complexType>

Remark: the combination of both is not allowed

<element name=“book” type=“Booktype”><complexType name=“Booktype”>

<element name=“title" type="string" /><element name="author" type="string" /><element name=“publisher" type="string" /><element name=“character" minOccurs="0"

maxOccurs="unbounded" /></complexType>

</element>

Building blocks: empty elements• Elements such as HTML tags <hr> or

<img ...> are empty<hr />

<img src=“image.gif” />

• Empty has to be declared as an implicit complex type

<element name=“img”><complexType content=“empty”>

<attribute name=“src” type=“string” /></complexType>

</element>

<element name=“hr”><complexType

content=“empty” /></element>

A level upwards ...• Let us define “bookshop”:<element name=“bookshop">

<complexType><element name=“book"

minOccurs="0” maxOccurs="unbounded"><complexType>

...</complexType>

</element></complexType>

</element>

A schema definition is a BOTTOM-UP process

Attribute definition

• Elements can have attributes associated to them• In DTDs, we would write:

<!ATTLIST book isbn #REQUIRED>

In XML Schema:<attribute name=“name of the attribute”

type=“type of the attribute”[options of the attribute ...]

>

Attribute definition• At the end of the element definition

<element name=“book" minOccurs="0" maxOccurs="unbounded"><complexType>

<element name=“title" type="string" /><element name="autor" type="string" /><element name=“publisher" type="string" /><element name=“character"

minOccurs="0" maxOccurs="unbounded" />

<attribute name="isbn" type="string" /></complexType>

</element>

General ordering

• The definitions are ordered for a better legibility:– 1) Simple types definition– 2) Attributes definition– 3) Complex types definition

Referencing the schema• We then add the schema reference in the XML

document: assume it is book.xml and bookshop is book.xsd then we would write:<?xml version="1.0" encoding="ISO-8859-1"?>

<bookshop

xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance”

xsi:noNamespaceSchemaLocation=“book.xsd”

>

...

</bookshop>

Namespaces

• An XML Namespace is a collection of names (of elements and attributes) identified by an URI

• Namespaces are a very flexible tool. The re-use of schemata, names, mixing them is promoted.

• For instance we could use elements from two name spaces< BOOKS>

<bk: BOOK xmlns:bk="urn: BookLovers.org:BookInfo“xmlns:money="urn:Finance:Money">

<bk:TITLE>A Suitable Boy</bk:TITLE><bk:PRICE money:currency="US Dollar">22.95</bk:PRICE>

</bk:BOOK></BOOKS>

Namespaces

• http://www.w3.org/2000/10/XMLSchema– This is the Namespace for the schemata. Suffix xsd is

used; if none, it is the default namespace

• http://www.w3.org/2000/10/XMLSchema-instance– Namespace for the documents instantiated from a

schema. The prefix xsi is usually used.

Example

<schema xmlns="http://www.w3.org/2000/10/XMLSchema ” 1

targetNamespace="http://www.upf.es/namespaces/Book” 2

elementFormDefault="qualified” 3

xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance”

xsi:schemaLocation=

"http://www.w3.org/2000/10/XMLSchema

http://www.w3.org/2000/10/XMLSchema.xsd"

xmlns:bk="http://www.publishing.org/namespaces/Book">

1 Indicates the default namespace, which is XMLSchema

2 Indicates that the elements and attributes in this schema are defined upon the namespace http://www.upf.es/namespaces/Book

3 Indicates that all the elements created in this namespace and used in the instantiated documents have to be qualified with a prefix (if we had used unqualified, only the global elements could go)

Example (2)

<schema xmlns="http://www.w3.org/2000/10/XMLSchema ”

targetNamespace="http://www.upf.es/namespaces/Book”

elementFormDefault="qualified”

xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance” 4

xsi:schemaLocation= 5

"http://www.w3.org/2000/10/XMLSchema 6

http://www.w3.org/2000/10/XMLSchema.xsd" 7

xmlns:bk=" http://www.upf.es/namespaces/Book">

4 Indicates that this XML document is instantiated from the general Schema on Schemata

5 This is the namespace where the attribute schemaLocation is defined

6 The namespace for the general Schema on Schemata

7 URI of this Schema on Schemata

Example (3)

<schema xmlns="http://www.w3.org/2000/10/XMLSchema ”

targetNamespace="http://www.upf.es/namespaces/Book”

elementFormDefault="qualified”

xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance”

xsi:schemaLocation=

"http://www.w3.org/2000/10/XMLSchema

http://www.w3.org/2000/10/XMLSchema.xsd"

xmlns:bk="http://www.upf.es/namespaces/Book">8

8 We give a prefix to the target namespace to facilitate the use in documents, for instance:

<element ref=“bk:Title" minOccurs="1" maxOccurs="1"/>

Example (and 4)• In the instantiated document:<bookshop xmlns ="http://www.upf.es/namespaces/Book”

1

xmlns:xsi="http://www.w3.org/2000/10/XMLSchema-instance” 2

xsi:schemaLocation=“http://www.upf.es/namespaces/book.xsd"> 3

1 We define the default namespace of the document

2 We include the namespace where schema instantiation is defined (xsi)

3 With schemaLocation we specify where is the Schema for this document (book.xsd)

Other important concepts

• ID and IDREFS

• DOM (Document Object Model)

• X-path

• X-pointer

• X-link

ID and IDREFS

• ID attribute for unique identification of element. Similar role of URI. Example assigning the identity “attack”:<paragraph id=“attack”>Suddenly the skies were filled with

aircraft</paragraph>

• IDREFS (identity reference) easiest way of referring to an ID. Example: In a DTD defined attributes of employee “empnumber” as an ID and “boss” as IDREFS; here we say that Hank’s ID is 126 and his boss is 124 (defined earlier):< employee empnumber=“emp126” boss=“emp124”>

Hank</employee>

DOM (Document Object Model)

• DOM is a technology for accessing and manipulating parts of an XML document

• DOM models a document as a tree whose nodes are its elements

• Then some properties and methods exist for the objects, allowing the access and manipulation

X-PATH

• X-Path is a language for referencing parts of an XML document

• It is used, for instance, to transform a document through XSL

• X-Path is based upon DOM; and uses paths (similar to URLs) to reference parts of a document

X-POINTER

• X-Pointer is a language for pointing at a part of an XML document

• X-Pointer uses X-path for pointing

• X-Pointer enables linking

Linking using XML: X-LINK

• X-Link is a language for describing how to link resources in XML

• We use attributes for the element link in the NameSpace xlink at "http://www.w3.org/XML/XLink/1.0"

• The attributes are used to describe end-points, traversal, effect, resources

Tools

• XML Browsers (visualisers)

• XML Editors

• XML Parsers

• XML Servers

• Relational DB to XML converters

• XSL Editors

• XSL Processors

XSL

Transformation Engine(XSL Parser)

XSL

XML HTML

• Allows to incorporate a design into an XML document, generating HTML, PDF, mail, SMS message, ...

• Using CSS and DSSSL (SGML)

XSL<?xml version="1.0"?><!DOCTYPE BookCatalogue SYSTEM "file://localhost/xml-course/xsl/BookCatalogue.dtd"><BookCatalogue> <Book> <Title>My Life and Times</Title> <Author>Paul McCartney</Author> <Date>July, 1998</Date> <ISBN>94303-12021-43892</ISBN> <Publisher>McMillin Publishing</Publisher> </Book> <Book> <Title>Illusions The Adventures of a Reluctant Messiah</Title> <Author>Richard Bach</Author> <Date>1977</Date> <ISBN>0-440-34319-4</ISBN> <Publisher>Dell Publishing Co.</Publisher> </Book> <Book> <Title>The First and Last Freedom</Title> <Author>J. Krishnamurti</Author> <Date>1954</Date> <ISBN>0-06-064831-7</ISBN> <Publisher>Harper &amp; Row</Publisher> </Book></BookCatalogue>

XSL

Document/

PI<?xml version=“1.0”?>

DocumentType<!DOCTYPE BookCatalogue ...>

ElementBookCatalogue

ElementBook

ElementBook

ElementBook

ElementTitle

ElementAuthor

ElementDate

ElementISBN

ElementPublisher

... ...

TextMy Life ...

TextPaul McCartney

TextJuly, 1998

Text94303-12021-43892

TextMcMillin Publishing

XSL

<?xml version="1.0"?><xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:template match="/"> <xsl:apply-templates/> </xsl:template> <xsl:template match="BookCatalogue"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Book"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Title"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Author"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Date"> <xsl:apply-templates/> </xsl:template> <xsl:template match="ISBN"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Publisher"> <xsl:apply-templates/> </xsl:template> <xsl:template match="text()"> <xsl:value-of select="."/> </xsl:template></xsl:stylesheet>

XSL<?xml version="1.0"?><xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> <xsl:template match="/"> <HTML> <HEAD> <TITLE>Book Catalogue</TITLE> </HEAD> <BODY> <xsl:apply-templates/> </BODY> </HTML> </xsl:template> <xsl:template match="BookCatalogue"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Book"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Title"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Author"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Date"> <xsl:apply-templates/> </xsl:template> <xsl:template match="ISBN"> <xsl:apply-templates/> </xsl:template> <xsl:template match="Publisher"> <xsl:apply-templates/> </xsl:template> <xsl:template match="text()"> <xsl:value-of select="."/> </xsl:template></xsl:stylesheet>

BookCatalogue.xsl

added these

XML-based formats

• XML is an architecture not an application– SMIL (Synchronized Multimedia Integration Language)

– RDF (Resource Description Framework) for metadata

– CDF (Channel Definition Format) canales Microsoft

– MathML (Mathematical Markup Language)

– CML (Chemical Markup Language)

– BSML (Bioinformatic Sequence Markup Language)

– JML

– WIDL (B2B integration)

Processing

• Two orientations to process XML documents using Java as programming language:

DOM (Document Object Model) tree structure (nodes, elements and text), most used

SAX (Serial Access with the Simple API for XML) event based Fastest, less memory requirements, more difficult to

program

Some references• http://www.w3.org/

– Official web with all the standards

• http://www.xml.com/– Web from O’Reilly publishers. A lot of good documentation and

resources.

• http://www.xfront.com/– Very good tutorials of XSL and XML-Schema

• http://xml.apache.org– Apache parsers and documentation (Xerces, Xalan, ...)

• XML and Java. B. McLAUGHLIN. O’Reilly, 2000– Interesting about their combination using Apache parsers