Unit 10: XML and Web
 eXtensible Markup Language
 “... is a simple, very flexible text format derived from SGML (ISO
8879). Originally designed to meet the challenges of large-scale
electronic publishing, XML is also playing an increasingly important
role in the exchange of a wide variety of data on the Web and
elsewhere. ”
W3 Consortium
 XML …
 is not a solution but a tool to build solutions
 is not a language but a meta-language that require
interoperating applications that use it to adopt clear conventions
on how to use it
 is a standardized text format that is used to represent structured
information
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SGML, XML and their applications
Meta-Markup Language
SGML
Application
Markup Language
XML
HyTime HTML
XHTML SMIL SOAP WML
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Well-Formed XML Documents
 The document has exactly one root element
 The root element can be preceded by an optional XML declaration
 Non-empty elements are delimited by both a start-tag and an end-tag.
 Empty elements are marked with an empty-element (self-closing) tag
 Tags may be nested but must not overlap
 All attribute values are quoted with either single (') or double (\") quotes
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<address>
<street>
<line>123 Pine Rd.</line>
</street>
<city name=\"Lexington\"/>
<state abbrev=\"SC\"/>
<zip base=\"19072\" plus4=\"\"/>
</address>
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Valid XML Documents
 Are well-formed XML documents
 Are documents that conform the rules defined by certain schemas
 Schema: define the legal building blocks of an XML document. It
defines the document structure with a list of legal elements. Two
ways to define a schema:
 DTD: Document Type Definition
 XML Schema
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DTD Example: Embedded and External Definitions
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<!DOCTYPE address [
<!ELEMENT address (street, city, state, zip)>
<!ELEMENT street line+>
<!ELEMENT line (#PCDATA)>
<!ELEMENT city (#PCDATA)>
<!ELEMENT state (#PCDATA)>
<!ELEMENT zip (#PCDATA)> ]>
<address> ... </address>
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<!DOCTYPE address SYSTEM
\"http://dtd.mycompany.com/address.dtd\">
<address> ... </address>
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DTD Limitations
 DTD is not integrated with Namespace technology so users cannot
import and reuse code
 DTD does not support data types other than character data
 DTD syntax is not XML compliant
 DTD language constructs are no extensible
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XML Schema: Example
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<xsd:schema xmlns:xsd=\"http://www.w3.org/2000/10/XMLSchema\"
elementFormDefault=\"qualified\">
<xsd:import namespace=\" \"/>
<xsd:element name=\"address\">
<xsd:complexType>
<xsd:sequence>
<xsd:element name=\"street\">
<xsd:complexType>
<xsd:all maxOccurs=\"unbounded\">
<xsd:element name=\"line\" type=\"xsd:string\"/>
</xsd:all>
</xsd:complexType>
</xsd:element>
<xsd:element name=\"city\" type=\"xsd:string\"/>
<xsd:element name=\"state\" type=\"xsd:string\"/>
<xsd:element name=\"zip\" type=\"xsd:string\"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>
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Processing XML Documents
 Using a programming language and the SAX API.
 SAX is a lexical, event-driven interface in which a document is
read serially and its contents are reported as \"callbacks\" to
various methods on a handler object of the user's design
 Using a programming language and the DOM API.
 DOM allows for navigation of the entire document as if it were a
tree of \"Node\" objects representing the document's contents.
 Using a transformation engine and a filter
 XSLT, XQuery, etc
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XML Uses
 Alternative/complement to HTML
 XML + CSS, XML + XSL, XHTML
 Declarative application programming/configuration
 Configuration files, descriptors, etc.
 Data exchange among heterogeneous systems
 B2B, e-commerce: ebXML
 Data Integration from heterogeneous sources
 Schema mediation
 Data storage and processing
 XML Databases, XQuery (XPath)
 Protocol definition
 SOAP, WAP, WML, etc.
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eXtensible Stylesheet Language: XSL
 XSL serves the dual purpose of
 transforming XML documents
 exhibiting control over document rendering
 XSL consists of two parts:
 XSL Transformations (XSLT):
 An XML language for transforming XML documents
 It uses the XML Path Language (XPath) to search and transverse
the element hierarchy of XML documents
 XSL Formatting Objects (XSL-FO):
 An XML language for specifying the visual formatting of an XML
document.
 It is a superset of the CSS functionally designed to support print
layouts.
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XQuery (XML Query): Example (source)
<bib>
<book year=\"1994\">
<title>TCP/IP Illustrated</title>
<author><last>Stevens</last><first>W.</first></author>
<publisher>Addison-Wesley</publisher>
<price>65.95</price>
</book>
<book year=\"1992\">
<title>Advanced Programming in the Unix environment</title>
<author><last>Stevens</last><first>W.</first></author>
<publisher>Addison-Wesley</publisher>
<price>65.95</price>
</book>
<book year=\"2000\">
<title>Data on the Web</title>
<author><last>Abiteboul</last><first>Serge</first></author>
<author><last>Suciu</last><first>Dan</first></author>
<publisher>Morgan Kaufmann Publishers</publisher>
<price>39.95</price>
</book>
</book>
</bib>
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XQuery (XML Query): Example (query)
<results>
{ let $a := doc(\"http://bstore1.example.com/bib/bib.xml\")//author
for $last in distinct-values($a/last),
$first in distinct-values($a[last=$last]/first)
order by $last, $first
return For each author, retrieve its last, first names as
<author> well as the title of its books, ordered by last, first
names
<name>
<last>{ $last }</last><first>{ $first }</first>
</name>
{ for $b in doc(\"http://bstore1.example.com/bib.xml\")/bib/book
where some $ba in $b/author
satisfies ($ba/last = $last and $ba/first=$first)
return $b/title }
</author> }
</results>
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XQuery (XML Query): Example (result)
<results>
<author>
<name>
<last>Abiteboul</last><first>Serge</first>
</name>
<title>Data on the Web</title>
</author>
<author>
<name>
<last>Stevens</last><first>W.</first>
</name>
<title>TCP/IP Illustrated</title>
<title>Advanced Programming in the Unix environment</title>
</author>
<author>
<name>
<last>Suciu</last><first>Dan</first>
</name>
<title>Data on the Web</title>
</author>
</results>
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A Smarter Web Is Possible
People and communities have data stores and applications to share
 Vision:
 Expand the Web to include more machine-understandable resources
 Enable global interoperability between resources you know should be
interoperable as well as those you don't yet know should be
interoperable
Key Web technologies:
 Web Services: Web of Programs
 Standards for interactions between programs, linked on the Web
 Easier to Expose and Use services (and data they provide)
 Semantic Web: Web of Data
 Standards for things, relationships and descriptions, linked on the Web
 Easier to Understand, Search for, Share, Re-Use, Aggregate, Extend
information
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Web Services
 “A Web service is a software system designed to support interoperable
machine-to-machine interaction over a network. It has an interface
described in a machine-processable format (specifically WSDL). Other
systems interact with the Web service in a manner prescribed by its
description using SOAP-messages, typically conveyed using HTTP with an
XML serialization in conjunction with other Web-related standards”. Web
Services Glossary, W3C, http://www.w3.org/TR/ws-gloss/
UDDI: Universal
Description,
Discovery and
Integration
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Simple Object Access Protocol (SOAP)
 SOAP is a simple XML based protocol to let applications exchange
information over HTTP.
 A SOAP message is a XML document containing the following
elements:
 A required Envelope element that identifies the XML document as a
SOAP message
 An optional Header element that contains header information
 A required Body element that contains call and response information
 An optional Fault element that provides information about errors that
occurred while processing the message
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SOAP Request: Example
POST /InStock HTTP/1.1
Host: www.stock.org
Content-Type: application/soap+xml; charset=utf-8
Content-Length: nnn
<?xml version=\"1.0\"?>
<soap:Envelope
xmlns:soap=\"http://www.w3.org/2001/12/soap-envelope\"
soap:encodingStyle=\"http://www.w3.org/2001/12/soap-
encoding\">
<soap:Body xmlns:m=\"http://www.stock.org/stock\">
<m:GetStockPrice>
<m:StockName>IBM</m:StockName>
</m:GetStockPrice>
</soap:Body>
</soap:Envelope>
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SOAP Response: Example
HTTP/1.1 200 OK
Content-Type: application/soap; charset=utf-8
Content-Length: nnn
<?xml version=\"1.0\"?>
<soap:Envelope
xmlns:soap=\"http://www.w3.org/2001/12/soap-envelope\"
soap:encodingStyle=\"http://www.w3.org/2001/12/soap-
encoding\">
<soap:Body xmlns:m=\"http://www.stock.org/stock\">
<m:GetStockPriceResponse>
<m:Price>34.5</m:Price>
</m:GetStockPriceResponse>
</soap:Body>
</soap:Envelope>
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Web Services Description Language (WSDL)
 A WSDL document describes a <definitions>
web service using these major <types>
elements: type definition ......
 <portType>: The operations </types>
performed by the web service <message>
 <message>: The messages message definition ...
used by the web service </message>
 <types>: The data types used
<portType>
by the web service
port definition ....
 <binding>: The communica- </portType>
tion protocols used by the web
<binding>
service
binding definition ..
</binding>
</definitions>
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WSDL Document: Example (fragment)
<message name=“getStockPriceRequest\">
<part name=\"StockName\" type=\"xs:string\"/>
</message>
<message name=“getStockPriceResponse\">
<part name=\"Price\" type=\"xs:float\"/>
</message>
<portType name=“StockMarket\">
<operation name=“getStockPrice\">
<input message=\"getStockPriceRequest\"/>
<output message=
\"getStockPriceTermResponse\"/>
</operation>
</portType>
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RESTful Web Services
 The overhead associated to SOAP makes it impractical in high-
traffic scenarios
 Representational State Transfer (REST): architectural style for
networked systems based on the following principles:
 Application state and functionality are abstracted into resources
 Every resource is uniquely addressable by an URI
 Client-Server: Clients pull resource representations
 Stateless: each request from client to server must contain all needed
information.
 Uniform interface: all resources are accessed with a generic interface
(HTTP-based)
 Interconnected resource representations
 Layered components - intermediaries, such as proxy servers, cache
servers, to improve performance, security
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RESTful Web Services (cont.)
 A RESTful web service is a simple web service implemented using
HTTP and the principles of REST.
 A RESTful web service is a collection of resources. Its definition
comprises:
 The URI for the web service as a whole (<baseURI>)
 A URI scheme to address individual resources, e.g. <baseURI>/<ID>
 The MIME type of the data supported by the web service (JSON, XML)
 The set of operations supported by the web service using HTTP
methods:
 POST: To create a resource on the server
 GET: To retrieve the current state of the resource
 PUT: To change the state of a resource or to update it
 DELETE: To remove or delete a resource
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RESTful WS: Example (adapted from Wikipedia)
Resource GET PUT POST DELETE
http://www.stock.org List the N/A Create a new N/A
/stocks members of entry in the
the collection where
collection. the ID is
For example assigned
list all the automatically by
stocks. the collection.
The ID created is
typically returned
by this operation.
http://www.stock.org Retrieve the Update the N/A Delete the
/stocks/IBM addressed addressed addressed
member of member of the member of
the collection collection or the
create it with a collection.
defined ID.
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Semantic Web = The Web of Data
 “The Web was designed as an information space, with the goal that
it should be useful not only for human-human communication, but
also that machines would be able to participate and help. One of the
major obstacles to this has been the fact that most information on
the Web is designed for human consumption, and even if it was
derived from a database with well defined meanings (in at least
some terms) for its columns, that the structure of the data is not
evident to a robot browsing the web. Leaving aside the artificial
intelligence problem of training machines to behave like people, the
Semantic Web approach instead develops languages for
expressing information in a machine processable form”.
 \"If HTML and the Web made all the online documents look like one
huge book, RDF, schema, and inference languages will make all
the data in the world look like one huge database\"
Tim Berners-Lee
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The Current Web
 Resources:
 Identified by URI's
 untyped
 Links:
 href, src, ...
 limited, non-descriptive
 Users:
 A lot of information, but its
meaning must be interpreted
and deduced from the content
as it has been done since
millenniums
 Machines:
 They don‟t understand.
dsbw 2008/2009 2q 25

The Semantic Web
 Resources:
 Globally identified by URIs
 or locally (Blank)
 Extensible
 Relational
 Links:
 Identified by URIs
 Extensible
 Relational
 Users:
 More an better information
 Machines:
 More processable information
(Data Web)
dsbw 2008/2009 2q 26

Semantic Web: How?
Make web resources more accessible to automated
processes
 Extend existing rendering markup with semantic markup
 Metadata annotations that describe content/function of web accessible
resources
 Use Ontologies to provide vocabulary for annotations
 “Formal specification” is accessible to machines
 A prerequisite is a standard web ontology language
 Need to agree common syntax before we can share semantics
 Syntactic web based on standards such as HTTP and HTML
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Semantic Web: It’s annotation, stupid!
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Semantic Web: Standards and Tools
RDF (Resource Description
Framework): simple data model to
describe resources and their
relationships
RDF Schema: is a language for
declaring basic class and types for
describing the terms used in RDF,
that allows defining class
hierarchies
SPARQL: SPARQL Protocol and
RDF Query Language
OWL: Web Ontology Language.
Allows enriching the description of
properties and classes, including,
among others, class disjunction,
association cardinality, richer data
types, property features (eg.
symmetry), etc.
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Resource Description Framework (RDF)
 RDF is graphical formalism ( + XML syntax + semantics)
 for representing metadata
 for describing the semantics of information in a machine-
accessible way
 RDF Statements are <subject, predicate, object> triples that
describe properties of resources :
<Carles,hasColleague,Ernest>
 XML representation:
<Description about=\"some.uri/person/carles_farre\">
<hasColleague
resource=\"some.uri/person/ernest_teniente\"/>
</Description>
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RDF Schema
 RDF Schema allows you to define vocabulary terms and the
relations between those terms
 it gives “extra meaning” to particular RDF predicates and
resources
 this “extra meaning”, or semantics, specifies how a term should
be interpreted
 Examples:
<Person,type,Class>
<hasColleague,type,Property>
<Professor,subClassOf,Person>
<Cristina,type,Professor>
<hasColleague,range,Person>
<hasColleague,domain,Person>
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Problems with RDFS
 RDFS too weak to describe resources in sufficient detail
 No localized range and domain constraints
 Can‟t say that the range of hasChild is person when applied to persons
and elephant when applied to elephants
 No existence/cardinality constraints
 Can‟t say that all instances of person have a mother that is also a
person, or that persons have exactly 2 parents
 No transitive, inverse or symmetrical properties
 Can‟t say that isPartOf is a transitive property, that hasPart is the
inverse of isPartOf or that touches is symmetrical
 …
 Difficult to provide reasoning support
 No “native” reasoners for non-standard semantics
 May be possible to reason via FO axiomatization
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Web Ontology Language (OWL)
 OWL is RDF(S), adding vocabulary to specify:
 Relations between classes
 Cardinality
 Equality
 More typing of and characteristics of properties
 Enumerated classes
 Three species of OWL
 OWL full is union of OWL syntax and RDF
 OWL DL restricted to FOL fragment (≅ SHIQ Description Logic)
 OWL Lite is “easier to implement” subset of OWL DL
 OWL DL Benefits from many years of DL research
 Well defined semantics
 Formal properties well understood (complexity, decidability)
 Known reasoning algorithms
 Implemented systems (highly optimised)
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OWL in RDF(S) notation: Example
Person ⊓ ∀hasChild.(Doctor ⊔ ∃hasChild.Doctor)
<owl:Class>
<owl:intersectionOf rdf:parseType=\" collection\">
<owl:Class rdf:about=\"#Person\"/>
<owl:Restriction>
<owl:onProperty rdf:resource=\"#hasChild\"/>
<owl:toClass>
<owl:unionOf rdf:parseType=\"collection\">
<owl:Class rdf:about=\"#Doctor\"/>
<owl:Restriction>
<owl:onProperty
rdf:resource=\"#hasChild\"/>
<owl:hasClass rdf:resource=\"#Doctor\"/>
</owl:Restriction>
</owl:unionOf>
</owl:toClass>
</owl:Restriction>
</owl:intersectionOf>
</owl:Class>
dsbw 2008/2009 2q 34

SPARQL Protocol And RDF Query Language
 Designed to query collections of triples…
 …and to easily traverse relationships
 Vaguely SQL-like syntax (SELECT, WHERE)
 “Matches graph patterns”
SELECT ?sal
WHERE { emps:e13954 HR:salary ?sal }
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SQL vs SPARQL
EMP_ID NAME HIRE_ SALARY emps:e13954 HR:name 'Joe'
DATE
emps:e13954 HR:hire-date 2000-04-14
13954 Joe 2000-04-14 48000 emps:e13954 HR:salary 48000
10335 Mary 1998-11-23 52000 emps:e10335 HR:name „Mary'
emps:e10335 HR:hire-date 1998-11-23
… … … … emps:e10335 HR:salary 52000
04182 Bob 2005-02-10 21750 …
SELECT hire_date SELECT ?hdate
FROM employees WHERE
WHERE salary >= 21750 { ?id HR:salary ?sal
?id HR:hire_date ?hdate
FILTER ?sal >= 21750 }
dsbw 2008/2009 2q 36

Semantic Web Services
Web Services
Dynamic UDDI, WSDL, SOAP Semantic Web Services
Static WWW Semantic Web
URI, HTML, HTTP RDF, RDF(S), OWL
 The main aim is to enable highly flexible Web services
architectures, where new services can be quickly discovered,
orchestrated and composed into workflows by
 creating a semantic markup of Web services that makes them
machine understandable and use-apparent is necessary
 developing an agent technology that exploits this semantic
markup to support automated Web service composition and
interoperability
dsbw 2008/2009 2q 37

References
 KAPPEL, Gerti et al. Web Engineering, John Wiley & Sons, 2006.
Chapter 14.
 SHKLAR, Leon and ROSEN, Rich. Web Application Architecture:
Principles, Protocols and Practices, 2nd Edition. John Wiley &
Sons, 2009. Chapters 5 and 13.
 www.w3.org
 www.w3schools.com
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