Media IT - XML and sublanguages

Media IT :: Dr Serge Linckels :: http://www.linckels.lu/ :: serge@linckels.lu ::
Faculty of Science, Technology and Communication (FSTC)
Bachelor en informatique (professionnel)
-- Media IT -–
¯_(ツ)_/¯
Unit 8
XML

8. XML and its Sub-Languages
2
8.1 Limitations of HTML
8.2 XML introduction
8.3 XML specifications
8.4 Document Definition Type (DTD)
8.5 XML Schema
8.6 Namespaces

3
<h1>Christoph Meinel</h1>
<h2>Viola Brehmer</h2>
<ul>
<li>Long Wang</li>
<li>Feng Cheng</li>
<li>Dirk Cordel</li>
<li>Serge Linckels</li>
</ul>
Harald Sack
Limitations of HTML
HTML was initiated to give a structure to a
document and to modify its layout; NOT to
describe semantics
What is this Web page about?
What position has "Viola Brehmer"?
…
Meta-Tags
<meta name="description"
content="Homepage of Serge Linckels">
<meta name="keywords"
content="teacher, athlete">
<meta name="Author"
content="The Master of the Universe">
<meta name="xyz"
content="nothing special">
Do you believe in Meta-Tags?
HTML metadata are created by the author of the Web page.
Their syntax and semantics are individual.

4
Extensible Markup Language (XML)
Markup Language: allows to give a structure to text documents
by using tags
Meta Language: XML does not have a fixed set of tags (new
tags can be created)
Extensible: XML can be adapted (extended) to meet many
different domains, e.g.,
• Mathematical Markup Language (MathML)
• Chemical Markup Language (CML)
• Synchronized Multimedia Integration Language (SMIL)
• WAP Markup Language (WML)
Creator Jon Bosak, 1996
XML is not…
a programming language
a network transport protocol
a database
XML is…
a simple data format
platform independent
does not require special applications

5
Picture created by Harald Sack

6
Picture created by Harald Sack

7
Standard Generalized Markup Language (SGML)
The Standard Generalized Markup Language
(SGML) is a metalanguage in which one can define
markup languages for documents
HTML XML


 XHTML
• Subset of SGML
• Structure of data
• Layout and data
are separated

8
Welcome to LIASIT
LIASIT stands for Luxembourg Advanced Studies in Information
Technology and since August 01, 2006 is a Doctoral School in the Faculty
of Science, Technology and Communication.
The faculty is composed of the following professors: David BASIN, Pascal
BOUVRY, Eric DUBOIS, Thomas ENGEL, Franck LEPREVOST, Christoph
MEINEL, Nicolas GUELFI, and Björn OTTERSTEN.
The PhD Students are: Christoph BRANDT, Pandu DEVARAKOTA, Daniel
FISCHER, Benjamin GATEAU, Markus GROSS, Joel GROTZ, Annie
GUERRIERO, Serge LINCKELS, Nicolas MAYER, Michael NOLL, Benoît RIES,
Michael STIEGHAHN.
Magali MARTIN is the secretary of LIASIT... and also a nice entertainer.
How we can see this…

9
Welcome to LIASIT
LIASIT stands for Luxembourg Advanced Studies in
Information Technology and since August 01, 2006 is a
Doctoral School in the Faculty of Science, Technology
and Communication.
The faculty is composed of the following professors:
David BASIN, Pascal BOUVRY, Eric DUBOIS, Thomas ENGEL,
Franck LEPREVOST, Christoph MEINEL, Nicolas GUELFI,
and Brn OTTERSTEN.
The PhD Students are: Christoph BRANDT, Pandu
DEVARAKOTA, Daniel FISCHER, Benamin GATEAU, Markus
GROSS, Joel GROTZ, Annie GUERRIERO, Serge LINCKELS,
Nicolas MAYER, Michael NOLL, Benot RIES, Michael
STIEGHAHN.
Magali MARTIN is the secretary of LIASIT... and also
a nice entertainer.
What a computer sees…

10
<title>Welcome to LIASIT</title>
<description>LIASIT stands for Luxembourg Advanced Studies
in Information Technology and since August 01, 2006 is
a Doctoral School in the Faculty of Science,
Technology and Communication.</description>
<profs>
<name>The faculty</name>
<name>is composed of</name>
<name>the following</name>
</profs>
<students>
<name>The PhD</name>
<name>Students are:</name>
<name>Christoph BRANDT,</name>
<name>Pandu DEVARAKOTA,</name>
</students>
<administration>
<name>Daniel FISCHER, <name>
</administration>
How we can help…

11
<title>Welcome to LIASIT</title>
<description>LIASIT stands for Luxembourg Advanced
Studies in Information Technology and since August 01,
2006 is a Doctoral School in the Faculty of Science,
Technology and Communication.</description>
<profs>
<name>The faculty</name>
<name>is composed of</name>
<name>the following</name>
</profs>
<students>
<name>The PhD</name>
<name>Students are:</name>
<name>Christoph BRANDT,</name>
<name>Pandu DEVARAKOTA,</name>
</students>
<administration>
<name>Daniel FISCHER, </name>
</administration>
How we can help…

12
<profs>
<name>Thomas Engel</name>
<name>Christoph Meinel</name>
<name>David Basin</name>
<name> Björn Ottersten</name>
</profs>
<students>
<name>Benoît Ries</name>
<name>Daniel Fischer</name>
<name>Christoph Brandt,</name>
<name>Pandu Devarakota</name>
<name>Serge Linckels</name>
</students>
Benefits of XML
Document is well-structured
Applications can process the file
XML file
Thomas Engel
Christoph Meinel
David Basin
Björn Ottersten
Benoît Ries
Daniel Fischer
Christoph Brandt
Pandu Devarakota
Serge Linckels
pure text file
Problems with text file
No structure
Difficult to process
Attention: although XML adds a certain amount of
semantics to the document, there are sill
information that are missing, e.g., what is the
relation between "profs" and "students"?

13
<person type="Teacher">
<hp>http://www.linckels.lu</hp>
<size>173</size>
<phone>691-111111</phone>
</person>
element
attribute
child-element
value
Terminology
Tree representation
person
name hp size phone
Serge Linckels
http://www.linckels.lu
173
691-111111
General
XML is composed of text and tags
Tags come in pairs, e.g., <hp></hp>
Tags must be properly nested, e.g.,
<person><hp></person></hp>
<person><hp></hp></person>
Tags are case sensitive: <hp> ≠ <HP>

14
<staff>
</staff>
XML structure
<size>173</size>
<phone>26 00 11 22</phone>
</person>
<name>Denis Zampunieris</name>
<phone>4666445290</phone>
</person>
same element can be used
repeatedly
Nested tags can be
part of a list too.
Order is not
significant.
Element or attribute?
<name>
<first>Serge</first>
<last>Linckels</last>
</name>
<name first="Serge" last="Linckels”></name>
Both variants are semantically identical
or

15
XML Names
Can include:
- letters (a..z, A..Z)
- digits (0..9)
- these punctuation chars:
- underscore (_)
- hyphen (-)
- period (.)
- special chars like ö, ç, Ω
Examples for valid XML Names:
<drivers_licence>
<_oki-doki>
<téléphone>
<this.works>
CDATA Sections
Everything between <![CDATA[ and ]]>
is treated as raw character data.
<![CDATA[This is just some
code that is ignored,
10 print "Hello world"
20 goto 10
]]>
<phone>26 00 11 22</phone>
</person>
Comments
Comments are between 
like in HTML

16
XML declaration
<?xml version="1.0" encoding="ASCII" standalone="yes"?>
<size>173</size>
</person>
encoding: XML is pure text, but can use different encoding, e.g.,
ASCII, Latin-1, Unicode, ISO-8859-1. When omitted then Unicode is
default.
standalone:
- "yes", no external DTD/Schema is given
- "no", external DTD/Schema is specified
XML-defined character sets
Unicode: 95156 characters from most of
Earths living languages (variants: UCS-2,
UCS-4, UTF-8, UTF-16)
ISO character sets: e.g., ISO-8859-15 (Latin
9) is ASCII + accented letters + €

17
JSON – Javascript Object Notation
No element names
Primary data format used for asynchronous
browser/server communication (AJAX)
Language-independent data format
Supported by many programming languages

Exercise

8.4 Document Type Definition (DTD)
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<name>
</name>
</person>
<Personne>
<Type>Teacher</Type>
<Nom>Serge Linckels</Nom>
<HP>http://www.linckels.lu</HP>
<Sexe>M</Sexe>
</Personne>
?
Formal syntax is required
DTD – Document Type Definitions
Syntax of XML document is described
Validating parser checks syntax:
XML document with DTD syntax
A XML document is valid if it respects the
syntax defined in its DTD
<!ELEMENT person (name, phone*)>
<!ELEMENT name (first, last)>
<!ELEMENT first (#PCDATA)>
<!ELEMENT last (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
#PCDATA: value of type string
A person-element can contain
1 name sub-element and 0..*
phone sub-elements
Attention: a document can be well-formed
but not valid!
Web browser only checks if well-formed.

20
<?xml version="1.0" standalone="no"?>
<!DOCTYPE person SYSTEM "http://www.linckels.lu/person.dtd">
<name>
</name>
</person>
person.xml
person.dtd
URI of the DTD-file
e.g., "/mydisk/person.dtd"
Validating a document
A Web browser does not validate documents
but only checks it for well-formedness
XML validators APIs are available in Java
Online validators, e.g.,
http://www.stg.brown.edu/service/xmlvalid/
http://www.w3.org/2001/03/webdata/xsv

21
<?xml version="1.0"?>
<!DOCTYPE person [
]>
<name>
</name>
</person>
Valid XML document with internal
DTD
Sequences
* Zero or more of the element is allowed
? Zero or one of the element is allowed
+ One or more of the element is required
Elements must appear in the specified order
Choices
<!ELEMENT color (red | green)
Here, the element color can have a child-
element red or green, not both at a time.

22
<!DOCTYPE person [
<!ATTLIST name first CDATA #IMPLIED
last CDATA #REQUIRED
>
]>
<name first="Serge" last="Linckels" />
</person>
Attribute declarations
Attribute defaults:
#IMPLIED: value is optional
#REQUIRED: value is required
#FIXED: value is constant
Literal: value is given as quoted string
Attribute types:
CDATA: any string of text
Enumeration: list of values
ID: unique XML name
IDREF: unique identification of some
element in the document
IDREFS: set of IDREFs
Valid XML document with internal DTD

23
<family>
<person id="jane" mother="mary" father="john">
<name>Jane Doe</name>
</person>
<person id="john" children="jane jack">
<name>John Doe</name>
</person>
<person id="mary" children="jane jack">
<name>Mary Smith</name>
</person>
<person id="jack" mother="mary" father="john">
<name>Jack Smith</name>
</person>
</family>
DTD – ID, IDREF and IDREFS
<!DOCTYPE family [
<!ELEMENT family (person*)>
<!ELEMENT person (name)>
<!ELEMENT name (#PCDATA)>
<!ATTLIST person
id ID #REQUIRED
mother IDREF #IMPLIED
father IDREF #IMPLIED
children IDREFS #IMPLIED>
]>
XML document
DTD

24
Problems and limitations
DTD are context-free grammars; recursive definitions are possible
Order matters, e.g.,
<!ELEMENT person (last, first)>
Workaround:
<!ELEMENT person ((last, first) | (first, last))>
Can become unclear:
<!ELEMENT person ((name | phone | e-mail)*)>
Lacks of expressiveness, e.g., restriction over references are not possible
All elements are global in one namespace
XML Schema, more powerful than DTD and W3C recommendation
No support for newer features of XML
DTD are expressed in a non-XML syntax
…but there are numerous other XML schema languages, e.g., RELAX NG, ISO DSDL, Schematron…

Exercise
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!DOCTYPE university [
<!ELEMENT university (teachers)>
<!ELEMENT teachers (teacher*)>
<!ELEMENT teacher (first, name, title, office?, teach*)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT office (#PCDATA)>
<!ELEMENT teach* EMPTY>
<!ATTLIST teach course IDREF #REQUIRED>
]>

8.5 XML Schema
27
XML Schema - Overview
XML Schema is an XML document containing a formal description of what comprises a valid
XML document
An XML document described by a schema is called an instance document
More explicit restrictions on the number and sequence of child elements are possible
Example
<fullName>Serge Linckels</fullname>
XML document
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="fullName" type="xs:string" />
</xs:schema>
XML Schema
xs: is standard
prefix for XML
Schema namespace

8.5 XML Schema
28
Atomic types (more than 40!)
string: Unicode string
integer: positive or negative number
boolean: true/false or 0/1
ID, IDREF, IDREFS: cf. DTD
Simple types
New simple types can be created by using atomic types
<xs:element name="first" type="xs:string" />
<xs:element name="age" type="xs:integer" />
<xs:element name="link" type="xs:anyURI" />
<xs:element name="year" type="xs:year" />
<xs:simpleType name="aName" base="xs:string" />
Restrictions can be defined
<xs:simpleType name="aName">
<xs:resriction base="xs:string>
<xs:maxLength value="50" />
</xs:restriction>
</xs:simpleType>

8.5 XML Schema
29
More about restrictions
Restrictions (facets) can be defined over simple types using xs:restriction
<xs:simpleType name="location">
<xs:enumeration value="work" />
<xs:enumeration value="school" />
<xs:enumeration value="mobile" />
</xs:restriction>
</xs:simpleType>
Enumerations:
<xs:simpleType name="age">
<xs:resriction base="xs:unsignedShort>
<xs:minExclusive value="0" />
<xs:maxInclusive value="120" />
</xs:restriction>
</xs:simpleType>
Numeric facets:
possible values:
• minInclusive
• maxInclusive
• minExclusive
• maxExclusive

8.5 XML Schema
30
More about restrictions
<xs:simpleType name="mobile-phone">
<xs:pattern value="ddd-dd dd dd" />
</xs:restriction>
</xs:simpleType>
Enforcing format:
Enforces the rule that a
mobile phone-number
consists of 3 digits, a
dash, 2 digits, a space, 2
digits, another space and
finally 2 digits.
<xs:simpleType name="TypeAuthor">
<xs:list itemType="xs:string />
</xs:simpleType>
Lists:
<xs:element name="author" type="TypeAuthor" />
XML Schema – element definition
XML Schema – simple type definition
The author element of an
instance document can
contain an unlimited list
of strings, each separated
by a whitespace

8.5 XML Schema
31
Complex types
A complex type is an element that contains
child-elements
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="person">
<xs:complexType>
<xs:sequence>
<xs:element name="last" type="xs:string" />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
<person>
</person>
XML document
XML Schema
Only elements can have complex types,
attributes always have simple types
sequence: order of elements matters (a,b)
all: order of elements does not matter (a,b or b,a)
choice: one or the other element (a xor b)

8.5 XML Schema
32
Occurrence Constraints
Set the number of times an element may occur:
minOccurs: minimum occurrences
maxOccurs: maximum occurrences
<xs:element name="middle" type="xs:string"
minOccurs="0" maxOccurs="unbounded“ />
The default value for minOccurs and maxOccurs is 1
In this example, maxOccurs is not set, but has a default value of 1. Therefore, the middle
element may appear 0 or 1 times.
The value unbounded indicates that the element may appear an unlimited number of times.

8.5 XML Schema
33
Derived complex types
Deriving by extension: add new definitions to existing complex type. E.g.,
add the phone element to the existing person type.
<xs:complexType name="PersonWithPhone">
<xs:extension base="person">
<xs:sequence>
<xs:element name="phone" type="xs:string" />
</xs:sequence>
</xs:extension>
</xs:complexType>
Deriving by restriction: by omitting parts of the parent definition, the
restriction element create a new, constrained type.
<xs:complexType name="PersonWithMoreNames">
<xs:restriction base="person">
<xs:sequence>
<xs:element name="first" type="xs:string" minOccurs="2" />
</xs:sequence>
</xs:restriction>
</xs:complexType>
Structure cannot be
changed!
Only available for
complex types

8.5 XML Schema
34
<xs:element name="person">
<xs:complexType>
<xs:sequence>
</xs:sequence>
<xs:attribute name="job" type="xs:string" />
</xs:complexType>
</xs:element>
Attribute declarations
Attributes can be declared globally by top-level xs:attribute
<xs:attribute name="job" type="xs:string" use="optional" />
Attributes can be declared locally as part of a complex type definition
<person job="Teacher">
</person>
possible values:
optional or required
XML document

8.5 XML Schema
35
Conclusion: DTD vs. XML Schemas
XML Schemas is a more powerful language than DTD to specify the syntax of XML
documents; therefore, it is more expressive in terms of semantics
XML Schemas is a W3C recommendation and widely used. As DTD are simpler to use, they
are still used today

8.6 Namespaces
36
<compactDisk author="HS">
<titel>Remixes</titel>
<track number="1">
<titel>Night over Manaus</titel>
<author>Boozoo Bajou</author>
</track>
</compactDisk>
Problem of ambiguous names
XML names can be used for different
elements. But this creates ambiguities.
XML namespaces disambiguate elements with the same name from each
other by assigning elements and attributes to URIs.
Qualified names, prefixes and local parts
Elements are identified by qualified names:
cd:titel
prefix local name
qualified name

8.6 Namespaces
37
Using XML namespaces
<cd:compactDisk
xmlns:cd = "http://www.linckels.lu/cd"
xmlns:tr = "http://www.xyz.com/tracks"
author="HS">
<cd:titel>Remixes</cd:titel>
<tr:track number="1">
<tr:titel>Night over Manaus</tr:titel>
<tr:author>Boozoo Bajou</tr:author>
</tr:track>
</cd:compactDisk>
Each element exists in a unique
namespace
Namespace URIs are purely formal
identifiers; they are not the
addresses of a page, and they are
not meant to be followed as links
<tr:title>Remixes</tr:title>
Instead of using a prefix, the complete URI can be indicated, e.g.,
<http://www.xyz.com/tracks#title>
Remixes
</http://www.xyz.com/tracks#title>
Namespace binding: each prefix in a qualified name must be associated with a URI
Namespaces only apply to elements,
not to attributes

38
XML in a Nutshell
Elliotte R. Harold, W. Scott Means, W. Scott Means
E-Librarian Service
User-Friendly Semantic Search in Digital Libraries
Serge Linckels, Christoph Meinel

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