XML and Related Technologies - Web Technologies (1019888BNR)

2 December 2005
Web Technologies
XML and Related Technologies
Prof. Beat Signer
Department of Computer Science
Vrije Universiteit Brussel
http://www.beatsigner.com

Beat Signer - Department of Computer Science - bsigner@vub.ac.be 2November 25, 2016
What is XML?
 Standardised text format for (semi-)structured
information
 Meta markup language
 tool for defining other markup languages
- e.g. XHTML, WML, VoiceXML, SVG, Office Open XML (OOXML)
 Data surrounded by text markup that describes the data
 ordered labeled tree
<note date="2013-10-17">
<to>Reinout Roels</to>
<from>Beat Signer</from>
<content>Let us discuss exercise 7 this afternoon ...</content>
</note>

... and What is it Not?
 XML is not a programming language
 however, it can be used to represent program
instructions, configuration files etc.
 note that there is an XML application (XSLT) which is
Turing complete
 XML is not a database
 XML is often used to store long-term data but it lacks many
database features
 many existing databases offer an XML import/export
 more recently there also exist native XML databases
- e.g. BaseX or eXist

XML Example
<?xml version="1.0"?>
<publications>
<publication type="inproceedings">
<title>An Architecture for Open Cross-Media Annotation Services</title>
<author>
<surname>Signer</surname>
<forename>Beat</forename>
</author>
<author>
<surname>Norrie</surname>
<forename>Moira</forename>
</author>
<howpublished>Proceedings of WISE 2009</howpublished>
<month>10</month>
<year>2009</year>
</publication>
<publication type="article">
...
</publications>

Evolution of XML
 Descendant of Standard Generalized Markup
Language (SGML)
 SGML is more powerful but (too) complex
 HTML is an SGML application
 XML was developed as a “SGML-Lite” version
 XML 1.0 published in February 1998
 Since the initial XML release numerous associated
standards have been published

Why has XML been so Successful?
 Simple
 General
 Accepted
 Many associated standards
 Many (freely) available tools

XML Specification
 Provides a grammar for XML documents in terms of
 placement of tags
 legal element names
 how attributes are attached to elements
 ...
 General tools
 parsers that can parse all XML documents regardless of particular
application tags
 editors and various programming APIs
 Specification available at http://www.w3.org/TR/xml/

XML Tree Document Structure
 An XML document tree can contain 7 types of nodes
 root node
- always exactly one root node
 element nodes
- element node with optional attribute nodes
 attribute nodes
- name/value pairs
 text nodes
- text belonging to an element or attribute
 comment nodes
 processing instruction nodes
- pass information to a specific application via <? ... ?>
 namespace nodes

Well-Formedness and Validity
 An XML document is well-formed if it follows
the rules of the XML specification
 An XML document can be valid according to its
Document Type Definition (DTD) or XML Schema
 completely self-describing about its structure and content through
- the document content
- auxiliary files referred to in the document
 validity can be checked by a validating XML parser
- online validation service available at http://validator.w3.org
<ELEMENT publication (title, author+, howpublished?, month, year)>
<ELEMENT title (#PCDATA)>
<ELEMENT author (surname, forename)>
<ATTLIST publication type CDATA>
…

Differences Between XML and HTML
 XML is a tool for specifying markup languages rather
than a markup language itself
 specify “special markup languages for special applications”
 XML is not a presentation language
 defines content rather than presentation
 HTML mixes content, structure and presentation
 XML was designed to support a number of applications
and not just web browsing
 XML documents should be well-formed and valid
 XML documents are easier to process by a program (parser)

Differences Between XML and HTML ...
 Readability is more important than conciseness
 e.g. <tablerow> rather than <tr>
 Matching of tags is case sensitive
 e.g. start tag <Bold> does not match end tag </BOLD>
 Markup requires matching start and end tags
 e.g. and 
 exceptions are special non-enclosing tags
e.g. or <image ... />
 Whitespaces in texts are significant

XHTML
 XHTML is a reformulation of HTML to make
it an XML application
 we accept that HTML is here to stay
 improve HTML it by using XML with minimal effort
 W3C stopped their work on XHTML (as discussed in lecture 3)
<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Vrije Universiteit Brussel</title>
</head>
<body>
...
</body>
</html>

Differences Between XHTML and HTML
 Documents must be valid
 XHTML namespace must be declared in <html> element
 <head> and <body> elements cannot be omitted
 <title> element must be the first element in the <head>
 End tags are required for non-empty clauses
 empty elements must consist of a start-tag and end-tag pair or an
empty element (e.g. )
 Element and attribute names must be in lowercase
 Attribute values must always be quoted
 Attribute names cannot be used without a value

XML Technologies
XPointerXLink
XPath
XQuery
XSLT

Overview of XML Technologies
 XPath and XPointer
 addressing of XML elements and parts of elements
 XSL (Extensible Stylesheet Language)
 transforming XML documents (XSLT) and XSL:FO
 XLink (XML Linking Language)
 linking in XML
 XQuery (XML Query Language)
 querying XML documents
 Document Type Definition (DTD) and XML Schema
 definition of schemas for XML documents
 DTDs have a very limited expressive power
 XML Schema introduces datatypes, inheritance etc.

Overview of XML Technologies ...
 SAX (Simple API for XML)
 event-based programming API for reading XML documents
 DOM (Document Object Model)
 programming API to access and manipulate XML documents as
tree structures
 RDF (Resource Description Framework)
 specific XML encoding used by the semantic web

Document Object Model (DOM)
 Defines a language neutral API for accessing and
manipulating XML documents as a tree structure
 have already seen the HTML DOM model
 The entire document must be read and parsed before it
can be used by a DOM application
 DOM parser not suited for large documents!
 Two different types of DOM Core interfaces for
accessing supported content types
 generic Node interface
 node type-specific interfaces
 Various available DOM parsers
 e.g. JDOM parser specifically for Java

Document Object Model (DOM) ...
 Different DOM levels
 DOM Level 1
- concentrates on HTML and XML document models
- contains functionality for document navigation and manipulation
 DOM Level 2
- supports XML Namespaces
- stylesheet object model and operations to manipulate it
 DOM Level 3
- specifies content models (DTD and Schemas)

XPath
 Expression language to address elements of an XML
document (used in XPointer, XSLT and XQuery)
 A location path is a sequence of location steps separated
by a slash (/)
 various navigation axes such as child, parent, following etc.
 have a look at our XSLT/XPath reference document that is
available on PointCarré for all the details about XPath
 XPath expressions look similar to file pathnames
/publications/publication
/publications/publication[year>2008]/title
//author[3]

XML Pointer Language (XPointer)
 Address points or ranges in an XML document
 Uses XPath expressions
 Introduces addressing relative to elements
 supports links to points without anchors

XML Linking Language (XLink)
 Standard way for creating links in XML documents
 Fixes limitations of HTML links where
 anchors must be placed within documents
 only entire documents or predefined marks (#) can be linked
 only one-to-one unidirectional links are supported
 XLinks can be defined in separate documents
 third-party link (metadata) server
 Two types of links
 simple links
- associate exactly one local and one remote resource (similar to HTML links)
 extended links
- associate an arbitrary number of resources

XML Linking Language (XLink) ...
 Other XLink features
 linking parts of resources
 links can be defined at
the attribute level
 typed links
 The Annotea project
uses XLink for managing
external annotations
 for example used in the
Amaya Web Browser
 New Microsoft Edge browser
 annotation of arbritatry webpages
Annotation in the Amaya Browser

Simple API for XML (SAX)
 Event-based API for XML document parsing
 many free SAX parsers available (e.g. Apache Xerces)
 Scans the document from start to end
 invokes callback methods
 Different kinds of events
 start of document
 end of document
 start tag of an element
 end tag of an element
 character data
 processing instruction
 SAX parser needs less memory than DOM parser
 DOM parser often uses SAX parser to build the DOM tree

XML Transformations
 Developers want to be able to transform data from one
format to another
 processing of XML documents
- XML to XML transformation
 post-processing of documents
- e.g. XML to XHTML, XML to WML, XML to PDF, ...
 The Extensible Stylesheet Language Transformations
(XSLT) language can be used for that purpose

XSLT Processor
 The XSLT processor (e.g. Xalan) applies an XSLT stylesheet to an
XML document and produces the corresponding output document
DTD
Source Tree Result Tree
Stylesheet Tree
DTD
XSLT Stylesheet
XML Document XHTML, WML, ...
DOM
Parser
XSLT
Processor
Input Document Output Document

XSL Transformations (XSLT)
 Most important part of XSL
 uses XPath for the navigation
 XSLT is an expression-based language based on
functional programming concepts
 XSLT uses
 pattern matching to select parts of documents
 templates to perform transformations
 Most web browsers support XSLT
 transformation can be done on the client side based on an XML
document and an associated XSLT document

Example
<publications>
<publication type="inproceedings">
<title>An Architecture for Open Cross-Media Annotation Services</title>
<author>
<surname>Signer</surname>
<forename>Beat</forename>
</author>
<author>
<surname>Norrie</surname>
<forename>Moira</forename>
</author>
<howpublished>Proceedings of WISE 2009</howpublished>
<month>10</month>
<year>2009</year>
</publication>
<publication type="article">
...
</publications>

XSLT Stylesheet
<xsl:stylesheet version="1.0" xmlns:xsl="http.w3.org/1999/XSL/Transform">
...
<xsl:template match="author">

<xsl:value-of select="surname"/>

</xsl:template>
...
</xsl:stylesheet>
<?xml version="1.0" encoding="utf-8"?>
<html>
...
Signer
Norrie
...
</html>
output

Other XSLT Statements
 <xsl:for-each select="...">
 select every XML element of a specified node-set
 <xsl:if test="...">
 conditional test
 <xsl:sort select="..."/>
 sort the output
 ...
 Have a look at the XSLT/XPath reference document that
is available on PointCarré
 in exercise 7 you will have the chance to implement and execute
different XSLT transformations

XML for Data Interchange
 Standard representation to exchange information
between different systems
 General way to query data from different systems
 e.g. via the XML Query (XQuery) language
 Connect applications running on different operating
systems and computers with different architectures
 XML Remote Procedure Call (XML-RPC)
 Simple Object Access Protocol (SOAP) which is a successor
of XML-RPC and used for accessing Big Web Services
- discussed later in the course

XML Remote Procedure Call (XML-RPC)
 XML-RPC specification released in April 1998
 Advantages
 XML-based lingua franca understood by different applications
 HTTP as carrier protocol
 not tied to a single object model (as for example in CORBA)
 easy to implement (based on HTTP and XML standards)
 lightweight protocol
 built-in error handling
 Disadvantages
 slower than specialised protocols that are used in closed
networks

XML-RPC Request and Response
POST /RPC2 HTTP/1.0
User-Agent: Java1.2
Host: macrae.vub.ac.be
Content-Type: text/xml;charset=UTF-8
Content-length: 245
<?xml version="1.0" encoding="ISO-8859-1"?>
<methodCall>
<methodName>Math.multiply</methodName>
<params>
<param>
<value><double>128.0</double></value>
</param>
<param>
</param>
</params>
</methodCall>
HTTP/1.1 200 OK
Connection: close
Content-Length: 159
Content-Type: text/xml
Server: macbain.vub.ac.be
<methodResponse>
<params>
<param>
</param>
</params>
</methodResponse>
XML-RPC Request XML-RPC Response

XML-RPC Error Message
HTTP/1.1 200 OK
Connection: close
Content-Length: 159
Content-Type: text/xml
Server: macbain.vub.ac.be
<methodResponse>
<fault>
<value>
<struct>
<member>
<name>faultCode</name>
<value><int>873</int></value>
</member>
<member>
<name>faultString</name>
<value><string>Error message</string></value>
</member>
</struct>
</value>
</fault>
</methodResponse>
XML-RPC Response

XML-RPC Scalar Values
XML-Tag Type Corresponding Java Type
<i4> or <int> four-byte signed integer Integer
<boolean> 0 or 1 Boolean
<string> ASCII string String
<double> double-precision signed float Double
<dateTime.iso8601> date/time Date
<base64> base64-encoded binary byte[]

XML-RPC Composed Values
 Complex data types can be represented by nested
<struct> and <array> structures
XML-Tag Type Corresponding Java Type
<struct> A structure contains
<member> elements and
each member contains a
<name> and a <value>
element
Hashtable
<array> An array contains a single
<data> element which can
contain any number of
<value> elements
Vector

OMX-FS
XML-RPC Example: GOMES
 Object-Oriented GUI for
the Object Model Multi-
User Extended Filesystem
 GOMES is implemented in
Java and uses XML-RPC
to communicate with the
Object Model Multi-user
Extended File System
(OMX-FS) which was im-
plemented in the Oberon
programming language
XML-RPC

Framework for Universal Client Access
 Generic database interface instead of developing a new
interface from scratch for each new device type
 The presented eXtensible Information Management
Architecture (XIMA) is based on
 OMS Java object database
- managing the application data
 Java Servlet Technology
 generic XML database interface
- separation of content and representation
 XSLT
- appropriate XSLT stylesheet chosen based on User-Agent HTTP header field

XIMA Architecture
OMS Java Workspace
OMS Java API
XML Server
HTML Servlet WML Servlet VXML Servlet
HTML
Browser
WML
Browser
VXML
Browser
Delegation
Builds XML
based on JDOM
XML + XSLT
→ Response
OM Model
Collections, Associations,
multiple inheritance and
multiple instantiation
Main Entry Servlet

Generic XIMA Interfaces
XHTML Interface WML Interface

Voice Interfaces
 Trend for ubiquitous information services
 small screens, keyboards etc. often clumsy to use
 Sometimes it is necessary to have hand-free interfaces
 e.g. while driving or operating a machine
 Alternative input modality for visually impaired users
 Voice interfaces can be accessed by a regular phone
 no new device is required
 no installation effort
 Improvements in speech recognition and text-to-speech
synthesis make automatic voice interfaces more feasible
 e.g. for call centers

VoiceXML Architecture
 Various solutions
 development: IBM WebSphere Voice Server SDK
 deployment: BeVocal Cafe Voice Portal
Speech
Recogniser
Converts voice
input into text
Speech model
Language
Analyser
Extracts meaning
from text
Grammar
Application
Server
Gets data (text)
from database
Application
database
Speech
Synthesiser
Generates
speech output
Pronounciation
rules
MeaningText Text
Voice Input Voice Output
Speech Speech

VoiceXML Architecture (for XIMA)
XIMA Framework
Apache
Web Server
Tomcat
OMS Java
Database
Websphere Voice
Server SDK
BeVocal
Voice Portal

Basic VoiceXML Concepts
 Dialogue
 conversational state in a form or menu
 form
- interaction that collects values for field item variables
 menu
- presents user with a choice of options
- transition to next dialogue based on choice
 Input
 recognition of spoken input (or recording of spoken input)
 recognition of DTMF (dual-tone multi-frequency) input
 Output
 speech synthesis (TTS)
 recorded audio files

VoiceXML Form Example
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd" version="2.0">
<form id="drinkForm">
<field name="drink">
<prompt>Would you like to order beer, wine, whisky, or nothing?</prompt>
<grammar src="drinks.grxml" type="application/srgs+xml"/>
</field>
<block>
<submit next="http://www.wise.vub.ac.be/drinks.php"/>
</block>
</form>
</vxml>

VoiceXML Menu Example
<?xml version="1.0" encoding="UTF-8"?>
<vxml xmlns="http://www.w3.org/2001/vxml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2001/vxml
http://www.w3.org/TR/voicexml20/vxml.xsd" version="2.0">
<menu id="mainMenu">
<prompt>
This is the main menu. What would you like to order? <enumerate/>
</prompt>
<choice next="#foodForm">food</choice>
<choice next="#drinkForm">drink</choice>
</menu>
...
</vxml>

associationscollections objects
The database contains #Collections and #Associations
Would you like to go to the collections, to the associations,
directly to an object or back to the main menu?
The database contains the
following # associations
Choose an association
Association 'name' contains #A
Would you like to list the
members or go back?
Association 'name' contains the
following # associations
Choose a 'domaintype' or
a 'rangetype' or say back
Object 'oID' is dressed with type 'type' and currently viewed as type 'type'. It contains #Attr, #Links, and #Methods
Choose a link
or say back
The object contains the
following # attributes
Would you like to hear the attributes, the links or
the methods or go back?
You can choose among
the following links
You can choose among
the following methods
You can view the object
as the following types
The database contains the
following # collections
Choose a collection
Collection 'name' contains #M
Would you like to list the
members or go back?
Collection 'name' contains the
following # members
Choose one of the members
The database contains #Objects
Choose an object or say back
Choose a method
or say back
Choose one of the
types or say back
The result of the
method is Result

Example: Avalanche Forecasting System
Project to provide WAP
and voice access

Other XML Applications
 Synchronized Multimedia Integration Language (SMIL)
 animations (timing, transitions etc.)
 Mathematical Markup Language (MathML)
 mathematical notations (content and structure)
 Scalable Vector Graphics (SVG)
 two-dimensional vector graphics (static or dynamic)
 Ink Markup Language (InkML )
 digital ink representation (e.g. from digital pen)
 Note that XML standards can also be combined
 e.g. XHTML+Voice Profile 1.0

Other XML Applications …
 Office Open XML (OOXML)
 file format (ZIP) for representing word processing documents,
presentations etc. (e.g. *.docx, *.pptx and *.xlsx)
- various XML files within these ZIP documents
- specific markup languages for different domains (wordprocessingML,
presentationML, spreadsheetML, …)
<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<p:sld xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main"
xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships"
xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main">
... <a:p>
<a:r><a:rPr lang="en-GB" dirty="0" smtClean="0" />
<a:t>Other XML</a:t>
</a:r>
<a:r><a:rPr lang="en-GB" dirty="0" smtClean="0" />
<a:t>Applications ...</a:t>
</a:r>
<a:endParaRPr lang="en-GB" dirty="0" />
</a:p> ...
</p:sld>
single slide from a pptx file

Exercise 7
 XML and Related Technologies

References
 Elliotte Rusty Harold and W. Scott Means,
XML in a Nutshell, O'Reilly Media, September 2004
 XML and XML Technology Tutorials
 http://www.w3schools.com
 Masoud Kalali, Using XML in Java
 http://refcardz.dzone.com/refcardz/using-xml-java
 VoiceXML Version 2.0
 http://www.w3.org/TR/voicexml20/
 VoiceXML Version 2.0
 http://www.w3.org/TR/voicexml20/

References ...
 Amaya Web Browser
 http://www.w3.org/Amaya/
 XML-RPC Homepage
 http://www.xmlrpc.com
 B. Signer et al., Aural Interfaces to Databases based
on VoiceXML, Proceedings of VDB6, Brisbane,
Australia, 2002
 http://beatsigner.com/publications/signer_VDB6.pdf
 eXtensible Information Management Architecture (XIMA)
 http://www.beatsigner.com/xima.html

2 December 2005
Next Lecture
Web 2.0 Patterns and Technologies

XML and Related Technologies - Web Technologies (1019888BNR)

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