Applications of XML
Web Services • RSS • RDF
Web Services
"Web services are
loosely coupled software components
delivered over
standard Internet technologies."
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Example Scenario: Get Online Information
Get Stock Price
Get Stock Price
Stock Exchange
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Return Stock
Price
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Return Stock
Price
Stock
Broker
Application
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Example Scenario – Online Trade
Buy The Hobbit (5)
The Hobbit (5)
Price: 20.95
Copies in Stock: 4
5
How
Buy
Much?
it
Book Store
Buy The Hobbit (5)
Book Store
20.95
The Hobbit (5)
Price: 25.95
1
Copies in Stock: 0
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Example Scenario: Grid Computation
Grid Computation
Using seamlessly
the combined
resources of
many computers
that are connected
to the Internet
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What is a Web Service?
• Self-contained, modular Web application that
can be published, located and invoked across
the Web
• A Web service can perform functions of
varying complexities
• Once deployed, other applications (and other
Web services) can discover and invoke the
deployed service
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Calling Remote Functions Could Help
• It would help if we could call functions, such as:
– Amazon.getPrice(“The Hobbit")
– Amazon.buyBook(“The Hobbit", myId)
getPrice(…)
The
Internet
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Difficulties in Using Remote Functions
• For each remote function, we need to phrase a
call in the specific language that is used for its
implementation
• For each remote function, we need to contact the
provider in order to find out what exactly the
signature (i.e., parameters, return value, inc. the
type) is
• On the server side, each remote function needs
to listen to a server socket bound to a specific
port
– Not in line with protection by firewalls
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The Solution
• Use an agreed interface and a syntax that all
applications are familiar with (e.g., XML)
– For example, SOAP
• Use HTTP to transfer data through port 80
• Use a standard for publishing methods, their
signatures and their usage
– For example, WSDL
• Use standard directory structures for publishing
available services
– For example, UDDI
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Web Services that are Already Available
• Google search (http://www.google.com/apis)
• Weather reports
• Stock prices
• Currency exchanges
• Sending SMS messages, faxes
• Prices of books in Barnes and Nobles
• Dictionaries
• etc.
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Implementing Web Services
• Programmers are given tools that spare the need
to directly write SOAP or WSDL documents
• In Java:
– JAX-RPC: part of SUN tools for publishing and
deploying Web Services
– AXIS: Apache’s tool for handling Web services in Java
• The combination of standards and management
tools (like Axis – next week) makes the invocation
of remote methods a very easy operation
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Programming the Services
• What programming language is used for Web
Services?
– They are independent from programming language
– HTTP can be implemented in any language
– XML contains data but not object (no methods, etc.)
• objects can be represented in XML and vice versa
– SOAP builds on top of XML (Infoset)
• Typical languages:
– Java, C#, Perl, PHP, Python, Ruby, …
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SOAP
Simple Object-Access Protocol
What is SOAP?
• SOAP is a protocol for accessing Web Services
• SOAP is XML based
– Thus, SOAP provides interoperability
• In SOAP, applications exchange information over
HTTP
– Thus, SOAP is not restricted by firewalls
• SOAP allows to exchange structured and typed
information on the Web
– XSchema types are used to add types to XML
• SOAP specification: http://www.w3.org/2000/xp/Group/
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SOAP Communication
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Soap Structure
Put a message into an envelope and describe
additional features in the header (payment, etc.)
SOAP Envelope
SOAP Header
- optional
SOAP Body
- required
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Fault
- optional
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POST /soap HTTP/1.0
SOAPAction: ""
Content-Length: 520
A request to
services.xmethods.net:80
<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope
xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soapenv:Body>
<ns1:getRate
soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:ns1="urn:xmethods-CurrencyExchange">
<country1 xsi:type="xsd:string">Euro</country1>
<country2 xsi:type="xsd:string">Israel</country2>
</ns1:getRate>
</soapenv:Body>
</soapenv:Envelope>
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HTTP/1.0 200 OK
Date: Sat, 07 May 2005 23:26:21 GMT
Content-Length: 492
The Response
Content-Type: text/xml
<?xml version='1.0' encoding='UTF-8'?>
<soap:Envelope
xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'
xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
xmlns:soapenc='http://schemas.xmlsoap.org/soap/encoding/'
soap:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'>
<soap:Body>
<n:getRateResponse
xmlns:n='urn:xmethods-CurrencyExchange'>
<Result xsi:type='xsd:float'>5.5825</Result>
</n:getRateResponse>
</soap:Body>
</soap:Envelope>
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Example - Calling Google Spelling
<?xml version="1.0" encoding="UTF-8" ?>
<SOAP-ENV:Envelope xmlns:SOAP
ENV=“http://schemas.xmlsoap.org/soap/envelope/”
xmlns:xsi=“http://www.w3.org/1999/XMLSchema-instance”
xmlns:xsd=“http://www.w3.org/1999/XMLSchema”>
<SOAP-ENV:Body>
<ns1:doSpellingSuggestion xmlns:ns1=“urn:GoogleSearch” SOAPENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<key xsi:type="xsd:string">00000000000000000000000000</key>
<phrase xsi:type="xsd:string">britney speers</phrase>
</ns1:doSpellingSuggestion>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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Example - Google Spelling Response
<?xml version="1.0" encoding="UTF-8" ?>
<SOAP-ENV:Envelope xmlns:SOAP
ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:xsi="http://www.w3.org/1999/XMLSchema-instance"
xmlns:xsd="http://www.w3.org/1999/XMLSchema">
<SOAP-ENV:Body>
<ns1:doSpellingSuggestionResponse xmlns:ns1="urn:GoogleSearch“
SOAPENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<return xsi:type="xsd:string">britney spears</return>
</ns1:doSpellingSuggestionResponse>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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MD5 Transform
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Baghdad Weather
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Baghdad Weather
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World Cities
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World Cities
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Messaging Patterns
• Synchronous
– Remote procedure call
– Standard HTTP request
response
• What are the limitations
here?
message
Client
Service
A
reply
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Asynchronous Messaging
• Asynchronous
– A message is sent with directions
on where to send the reply when
it is ready.
• Generalize the callback model
Service
A
– Document oriented
– Tolerates long latencies
• Destination of reply may be
different from origin
message
Client
• Message may transit several
other services
• Analogy: Mail, Email, … To:
From:
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Reply
Dest.
Service
B
Service
c
reply
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The SOAP Header
• A generic mechanism for adding features to a SOAP message
• Contained in the header are header blocks
– Some header blocks are marked as mandatory (mustUnderstand=“true”)
the rest can be ignored.
• The header blocks contain answers to questions like
– Where to send a reply or fault message
• i.e. how to handle asynchronous messaging
– What are the security requirements of this message
– Other “policy” issues that are involved
– Used by the reliable message protocol
• The header is the place where protocol composability takes place
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WS-Addressing
• A soap header used to
– Specify the final
<S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope"
destination and action
xmlns:wsa="http://www.w3.org/2004/12/addressing">
of a message
<S:Header>
– A unique identifier for <wsa:To>http://Z.com/ServiceURI</wsa:To>
<wsa:Action>http://Z.com/DoSomething</wsa:Action>
the message
<wsa:MessageID>
– The endpoint of a reply
http://example.com/SomeUniqueMessageIdString
– The endpoint of a fault </wsa:MessageID>
message
<wsa:ReplyTo>
<wsa:Address>http://X.com/someClient</wsa:Address>
– The details of an
</wsa:ReplyTo>
endpoint
<wsa:FaultTo>
reference
<wsa:Address>http://Y.com//ErrorHandler</wsa:Address>
</wsa:FaultTo>
</S:Header>
<S:Body>
<!-- The message body of the SOAP request appears here -->
</S:Body>
</S:Envelope>
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What is an endpoint reference?
• Specifies the complete details about how to get to
and identify a service
– My address …
• The simplest form
– <wsa:Address>http://X.com/myservice</wsa:Address>
• But more complex forms are possible
– For example qualifying a level of service
<wsa:EndpointReference xmlns:wsa="..." xmlns:painter="...">
<wsa:Address>http://housepainting.com</wsa:Address>
<wsa:ReferenceProperties>
<painter:ServiceLevel>Basic Paint Job</painter:ServiceLevel>
</wsa:ReferenceProperties>
</wsa:EndpointReference>
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Some More Details on SOAP
encodingStyle Attribute
• “The SOAP encodingStyle attribute indicates the encoding rules
used to serialize parts of a SOAP message”
– Needed when sending data structures
• This attribute may appear on any SOAP element, and it will apply to
that element's content and all child elements
• A SOAP message has no default encoding
– Unencoded data may be used in SOAP messages
• The SOAP default XMLSchema for SOAP encoding and data
types is:
http://www.w3.org/2002/12/soap-encoding
– Other encoding rules may be used
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SOAP Header Element
• The SOAP Header element is optional
• It contains application-specific information (like
authentication, payment, etc.) about the SOAP message
• If the Header element is present, it must be the first child
element of the Envelope element
• Attributes that the namespace defines:
– Role – used to address the Header element to particular
servers (relevant to p2p scenarios where a message can
reach several servers)
– mustUnderstand – used to indicate whether a header entry
is mandatory or optional for the recipient to process
– encodingStyle – as explained before
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SOAP Header Element
• Example:
<SOAP-ENV:Header>
<t:Transaction xmlns:t="some-URI"
SOAP-ENV:mustUnderstand="1">5
</t:Transaction>
</SOAP-ENV:Header>
• 5 is the transaction ID of which this method is a part
• In the above example, the SOAP-envelope attribute mustUnderstand is
set to 1, which means that the server must either understand and honor
the transaction request or must fail to process the message
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SOAP Response on Error
• There can be many errors in processing a SOAP request
• Error in Running Methods: For example, suppose that the
"Hello Server" does not allow anyone to say hello on
Tuesday
• Error in Processing SOAP Headers: For example, a
problem running the method as a part of a transaction
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The Fault Element May Include the
Following Sub-Elements
• <faultcode> : A code for identifying the fault
• <faultstring> : A human readable explanation of
the fault
• <faultactor> : Information about who caused the
fault
• <detail> : Holds application-specific error
information related to the Body element of the
SOAP request
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SOAP Fault Codes
• VersionMismatch: Found an invalid namespace for
the SOAP Envelope element
• MustUnderstand: An immediate child element of the
Header element, with the mustUnderstand attribute
set to 1, was not understood
• Client: The message was incorrectly formed or
contained incorrect information
• Server: There was a problem with the server so the
message could not proceed
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SOAP Error Response for Method Error
<SOAP-ENV:Envelope xmlns:SOAP-ENV="
http://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Body>
<SOAP-ENV:Fault>
<faultcode>SOAP-ENV:Server</faultcode>
<faultstring>Server Error</faultstring>
<detail>
<e:myfaultdetails xmlns:e="Hello">
<message>
Sorry, I cannot say hello on Tuesday.
</message>
<errorcode>1001</errorcode>
</e:myfaultdetails>
</detail>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
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SOAP Error Response for Header Error
<SOAP-ENV:Envelope xmlns:SOAP-ENV="
http://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Body>
<SOAP-ENV:Fault>
<faultcode>SOAP-ENV:MustUnderstand</faultcode>
<faultstring>SOAP Must Understand
Error</faultstring>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
No detail element may appear when there is an error
in processing the Headers of a SOAP request
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Sending a Request
• The SOAP request does not contain the address
to which it should be sent
• Q: Where do we put the URL of the Web Service?
• A: It depends on the protocol used to send the
request (usually HTTP, but could also be another
protocol, e.g., SMTP)
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SOAP Request via HTTP
POST http://www.Hello.com/HelloApplication HTTP/1.0
Content-Type: text/xml; charset=UTF-8
Content-Length: 587
SOAPAction: urn:helloApp
<SOAP-ENV:Envelope …
Note: There are 2 addresses
(1) URL of a SOAP Server
(2) URI of an application to run (this needn't
correspond to an actual Internet address)
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SOAPAction Header
• Used to indicate the intent of the SOAP HTTP request
• The presence and content of the SOAPAction header field
can be used by servers, such as firewalls, to appropriately
filter SOAP request messages in HTTP
• The header-field value of an empty string ("") means that
the intent of the SOAP message is provided by the URL of
the HTTP Request
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WSDL
Web Services Definition Language
Describing a Web Service
• Need a standard way to describe a Web Service:
– the methods available
– their parameters
– etc.
• WSDL is a standard for describing Web services
using XML, i.e., it is a language for the green
pages of UDDI
• WSDL specification can be found at
http://www.w3.org/TR/wsdl
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The Web Service Definition Language
• A document used by a
client so that it has a
formal description of a
service
Service Registry
• Client fetches the WSDL
for a service from some
location
WSDL for
Service X
1
• Client uses the WSDL to
properly format the
SOAP request and to
understand the reply
2
3
Service
X
message
Client
4
reply
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WSDL Can Describe
• What a Web service can do
• Where it resides
• How to invoke it
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The Structure of a WSDL Document
<definition>
<type>
definition of a type
</type>
<definition>
<message>
definition of a message
<types>
</message>
<portType>
def. of operations (composed of messages)
<messages>
</portType>
<binding>
how to translate operations into SOAP
</binding>
<portTypes>
<bindings>
<service>
the location of the service
<service>
</service>
</definition>
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<?xml version="1.0"?>
<definitions name="CurrencyExchangeService"
targetNamespace="http://www.xmethods.net/sd/CurrencyExchangeService.wsdl"
xmlns:tns="http://www.xmethods.net/sd/CurrencyExchangeService.wsdl"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<message name="getRateRequest">
<part name="country1" type="xsd:string"/>
<part name="country2" type="xsd:string"/>
</message>
<message name="getRateResponse">
<part name="Result" type="xsd:float"/>
</message>
<portType name="CurrencyExchangePortType">
<operation name="getRate">
<input message="tns:getRateRequest" name="getRate"/>
<output message="tns:getRateResponse"
name="getRateResponse"/>
</operation></portType>
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<binding name="CurrencyExchangeBinding" type="tns:CurrencyExchangePortType">
<soap:binding style="rpc" transport="http://schemas.xmlsoap.org/soap/http"/>
<operation name="getRate">
<soap:operation soapAction=""/>
<input name="getRate">
<soap:body use="encoded" namespace="urn:xmethods-CurrencyExchange"
encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
</input>
<output name="getRateResponse">
<soap:body use="encoded" namespace="urn:xmethods-CurrencyExchange"
encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"/>
</output>
</operation>
</binding>
<service name="CurrencyExchangeService">
<documentation>Returns the exchange rate between the two currencies</documentation>
<port name="CurrencyExchangePort" binding="tns:CurrencyExchangeBinding">
<soap:address location="http://services.xmethods.net:80/soap"/>
</port>
</service>
</definitions>
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The Elements of WSDL Documents
• Types – containing XML Schema element and type
definitions
• Message – an abstract typed definition of the data
being communicated
• Operation – an abstract description of an action
supported by the service
• Port Type – an abstract set of operations supported
by one or more endpoints
• Binding – a concrete communication protocol and
data format specification for a particular port type
• Port – a single endpoint defined as a combination of
a binding and a network address
• Service – a collection of named ports, each
associated with a binding and a network address
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Putting it together
• A client uses the wsdl to guide
the creation of the body of the
soap message
• The header of the soap
message is primarily used to
add additional protocol
information
Service Registry
WSDL for
Service X
– For example, the wsdl does
not tell us where to send the
reply
– So far it does not tell us about
security or reliability
requirements or other policy
issues
1
2
3
Service
X
message
Client
4
reply
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Really Simple Syndication
What is RSS?
• RSS is used for effectively publishing headlines
and frequently updated content
• RSS files (also called RSS feeds) are XML that
conform to a very simple schema
• Publishers make the RSS feed available on the
Web
– ynet: http://www.ynet.co.il/Integration/StoryRss2.xml
– cnn: http://rss.cnn.com/rss/cnn_topstories.rss
– Intel products: http://rss.intel.com/rss/intel-products.xml
• RSS readers are responsible for being updated
– That is, have the most recent copy of the feed
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So Why RSS?
• A standard, unified way of distributing headlines
– Application readers need only to know the feed URL
– Easy to query (“anything new about the middle east?”)
and integrate news from multiple sources
• Efficiency: RSS feeds typically contain a small
fragment of text for each news item
– Thus, a lot of traffic is saved
– Compare it to downloading the Web page of the
publishing company
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Mozilla’s Reader
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Goggle’s Reader
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Example: Ynet Feed
<?xml version="1.0" encoding="Windows-1255"?>
<rss version="2.0">
<channel>
<title>ynet - Updates for RSS</title>
<link>http://www.ynetnews.com/home/0,7340,L-3254,00.html</link>
<description></description>
<copyright>Ynet - news and content from Israel (Yedioth Ahronoth web site)</copyright>
<language> en </language>
<pubDate>Sun, 15 Apr 2007 00:03:31 +0200</pubDate>
<lastBuildDate> Sun, 15 Apr 2007 00:03:31 +0200 </lastBuildDate>
<image>
<title>Ynet</title>
<link>http://www.ynetnews.com/home/0,7340,L-3254,00.html</link>
<url>http://www.ynetnews.com/images/ECENTRAL_logo.gif</url>
</image>
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Example: Ynet Feed (cont’d)
<item>
<category>Updates</category>
<title>Egypt pours cold water on talk of &quot;Negotiations&quot; </title>
<description></description>
<link>http://www.ynetnews.com/articles/0,7340,L-3387877,00.html</link>
<pubDate>Sat, 14 Apr 2007 23:51:24 +0200</pubDate>
<guid>http://www.ynetnews.com/articles/0,7340,L-3387877,00.html</guid>
</item>
<item>
<category>Updates</category>
<title>US: N. Korea must immediately invite IAEA inspectors</title>
<description></description>
<link>http://www.ynetnews.com/articles/0,7340,L-3387866,00.html</link>
<pubDate>Sat, 14 Apr 2007 22:30:39 +0200</pubDate>
<guid>http://www.ynetnews.com/articles/0,7340,L-3387866,00.html</guid>
</item>
<item> …
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The Channel Element
• This element represents the feed itself
• A channel contains item elements and, in
addition, other elements that describe the feed
• Three sub-elements are required title, link
and description
• The channel of the previous example had also an
image and a language sub-elements
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The item Element
• Each item element defines one news item
• An item has three mandatory sub-elements:
– The title of the item
– A description of the item
– A link (usually, points to a Web interface of the item)
• Optional sub-elements:
– pubDate – date of publication
– comments – a link to comments about the item
– category
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Title, Link
Description
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Resource Description Framework
The Semantic Web Vision
• The vision of the semantic-Web activity is that
Web data will entail the semantics of data in a
manner that is understood (and can be
processed) automatically by computers
– Common formats
– Documents integrate data from diverse resources
(rather than invent their own specific objects)
– A language that specifies how the data relates to realworld objects
• Instantiated by developing a variety of languages
and specifications (RDF, SPARQL, OWL, …)
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What is RDF?
• A part of the semantic-Web activity
• RDF is a general-purpose language for
representing information on the Web
– Specifically, objects and relationships
• Designed to allow computer applications to
process data based on its semantics
– Rather than displaying data to humans (as opposed to
RSS)
• An RDF document is actually a labeled graph that
is represented in XML
– The specific language is called RDF/XML
– W3C recommendation (Feb. 2004)
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RDF Data
The basic element: Triple (labeled edge)
Subject
RDF document:
edge-labeled graph
predicate
Object
Person#845
address
#1002
street
Herzel
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postalCode
6941
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The XML Syntax of RDF
John Smith
page.html
John’s Home Page
<?xml version=“1.0”?>
<rdf:RDF
xmlns:rdf=“http://www.w3.org/TR/WD-rdf-syntax#”
xmlns:dc=“http://purl.org/metadata/dublin_core#”>
<rdf:Description about=“page.html”>
<dc:Creator>John Smith</dc:Creator>
<dc:Title>John’s Home Page</dc:Title>
</rdf:Description>
</rdf:RDF>
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Structured Values
page.html
dc:Creator
dc:Title
John’s Home Page
Name
John Smith
Email
js@corp.com
...
<Description about=“page.html”>
<dc:Creator>
<Description>
<corp:Name>John Smith</corp:Name>
<corp:Email>js@corp.com</corp:Email>
</Description>
</dc:Creator>
<dc:Title>John’s Home Page</dc:Title>
</Description>
</RDF>
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Dublin Core
• A set of fifteen basic properties for describing
generalized Web resources
• The “obvious” mapping of Dublin Core
properties into RDF properties has not yet
been approved by the Dublin Core initiative,
but is generally a good example
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Dublin Core
• “Title”: the name given to the resource
• “Creator”: the person or organization primarily
responsible for the resource
• “Subject”: what the resource is about
• “Description”: a description of the content
• “Publisher”: the person or organization
responsible for making the resource available
• “Contributor”: someone who has provided content
to the resource other than the creator
• “Date”: date of creation or publication
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Dublin Core
• “Type”: type of resource, such as home page, technical
report, novel, photograph…
• “Format”: data format of the resource
• “Identifier”: URL, ISBN number, …
• “Source”: another resource that this resource is derived
from
• “Language”: the language of the content
• “Relation”: another resource and its relationship to this one
• “Coverage”: the portion of time or space described by this
resource (atlases, histories, etc.)
• “Rights”: the intellectual property rights adhering to this
resource, or a pointer to them
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Concise Introduction to RDF:
Found in www.vanx.org, by
Yuri Khramov, SchemaSoft
Outline
1. Semantic Web Initiative and Metadata
2. Resource Description Framework (RDF)
basics
3. Advanced topics: collections, reification
4. Vocabularies: Dublin Core, RSS,..
5. RDF Schema
6. How to get RDF to work?
7. Conclusion
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Semantic Web
The Web was built for human consumption, and
although everything on it is machine-readable, this
data is not machine-understandable
Semantic Web -- a web of data that can be
processed directly or indirectly by machines
The solution proposed here is to use metadata to
describe the data contained in the Web
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RDF Basics
• Resources
• Properties that have Values
• Statement: Resource A has property B with
Value C
B
C
A
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www.vanx.org/presentations/RDF
Author
Name
Mail address
Yuri
Khramov
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Yurik@schemasoft.com
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Advanced RDF
• Containers: bags, sequences, alternatives
• aboutEach, aboutEachPrefix
• Reification (higher order statements)
• Namespaces and Vocabularies
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Dublin Core et al.
• Defined as Open Metadata
• Usual “Library Catalog” Elements, like Creator, Title,
Publisher, Date, Language
• Extended by: Source, Relations,Type (what is it – text,
image, software), Format
• URI (Identifier)
• Used for cataloging “Global Web Library”
• Others: RSS (RDF Site Summary) – NetScape,
• PRISM – publishing – Adobe, Quark, ..
• <indecs> - e-business – EU companies
•
RDF mappings for P3P, PICS,…
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RDF Schema
• Not an XML Schema!
• A “companion” specification for RDF spec
• Class, Type, subClassOf,
• domain, range
• Misc: label, comment, isDefinedBy,etc.
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Creating RDF documents
• Manually from HTML or “user domain XML”
• With special assisting tools – like Protégé,
Reggie, DC-dot, RDF for XML
• Ideally – with some automated procedure from
HTML/XML documents
• Can we use XSLT there?
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Can we use RDF now?
• IBM’s Java Central Station (uses RDF)
• Mozilla’s Aurora (RDF-based)
• MUZE DATAX project
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