Applications of XML Web Services RSS

Applications of XML Web Services • RSS • RDF

Web Services

"Web services are loosely coupled software components delivered over standard Internet technologies. " DBI 2007 HUJI-CS 3

Example Scenario: Get Online Information Get Stock Price Stock Exchange DBI 2007 Return Stock Price HUJI-CS Return Stock Price Stock Broker Application 4

Example Scenario – Online Trade Buy The Hobbit (5) Price: 20. 95 Copies in Stock: 4 Copies in Stock: 5 How Much? Buy it Book Store Buy The Hobbit (5) Book Store 20. 95 The Hobbit (5) Price: 25. 95 Copies in Stock: 0 Copies in Stock: 1 DBI 2007 HUJI-CS 5

Example Scenario: Grid Computation Using seamlessly the combined resources of many computers that are connected to the Internet DBI 2007 HUJI-CS 6

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 DBI 2007 HUJI-CS 7

Calling Remote Functions Could Help • It would help if we could call functions, such as: – Amazon. get. Price(“The Hobbit") – Amazon. buy. Book(“The Hobbit", my. Id) get. Price(…) The Internet DBI 2007 HUJI-CS 8

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 DBI 2007 HUJI-CS 9

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 DBI 2007 HUJI-CS 10

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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. DBI 2007 HUJI-CS 12

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 DBI 2007 HUJI-CS 13

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, … DBI 2007 HUJI-CS 14

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. w 3. org/2000/xp/Group/ DBI 2007 HUJI-CS 16

SOAP Communication DBI 2007 HUJI-CS 17

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 DBI 2007 HUJI-CS Fault - optional 18

POST /soap HTTP/1. 0 SOAPAction: "" Content-Length: 520 A request to xmethods. net: 80. services <? xml version="1. 0" encoding="UTF-8"? > <soapenv: Envelope xmlns: soapenv="http: //schemas. xmlsoap. org/soap/envelope/" xmlns: xsd="http: //www. w 3. org/2001/XMLSchema" xmlns: xsi="http: //www. w 3. org/2001/XMLSchema-instance"> <soapenv: Body> <ns 1: get. Rate soapenv: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/" xmlns: ns 1="urn: xmethods-Currency. Exchange"> <country 1 xsi: type="xsd: string">Euro</country 1> <country 2 xsi: type="xsd: string">Israel</country 2> </ns 1: get. Rate> </soapenv: Body> </soapenv: Envelope> DBI 2007 HUJI-CS 19

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. w 3. org/2001/XMLSchema-instance' xmlns: xsd='http: //www. w 3. org/2001/XMLSchema' xmlns: soapenc='http: //schemas. xmlsoap. org/soap/encoding/' soap: encoding. Style='http: //schemas. xmlsoap. org/soap/encoding/'> <soap: Body> <n: get. Rate. Response xmlns: n='urn: xmethods-Currency. Exchange'> <Result xsi: type='xsd: float'>5. 5825</Result> </n: get. Rate. Response> </soap: Body> </soap: Envelope> DBI 2007 HUJI-CS 20

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. w 3. org/1999/XMLSchema-instance” xmlns: xsd=“http: //www. w 3. org/1999/XMLSchema”> <SOAP-ENV: Body> <ns 1: do. Spelling. Suggestion xmlns: ns 1=“urn: Google. Search” SOAP- ENV: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/"> <key xsi: type="xsd: string">0000000000000</key> <phrase xsi: type="xsd: string">britney speers</phrase> </ns 1: do. Spelling. Suggestion> </SOAP-ENV: Body> </SOAP-ENV: Envelope> DBI 2007 HUJI-CS 21

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. w 3. org/1999/XMLSchema-instance" xmlns: xsd="http: //www. w 3. org/1999/XMLSchema"> <SOAP-ENV: Body> <ns 1: do. Spelling. Suggestion. Response xmlns: ns 1="urn: Google. Search“ SOAPENV: encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/"> <return xsi: type="xsd: string">britney spears</return> </ns 1: do. Spelling. Suggestion. Response> </SOAP-ENV: Body> </SOAP-ENV: Envelope> DBI 2007 HUJI-CS 22

MD 5 Transform DBI 2007 HUJI-CS 23

Baghdad Weather DBI 2007 HUJI-CS 24

Baghdad Weather DBI 2007 HUJI-CS 25

World Cities DBI 2007 HUJI-CS 26

World Cities DBI 2007 HUJI-CS 27

Messaging Patterns • Synchronous – Remote procedure call – Standard HTTP request response • What are the limitations here? message Client Service A reply DBI 2007 HUJI-CS 28

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: DBI 2007 HUJI-CS Reply Dest. Service B Service c reply 29

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 (must. Understand=“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 DBI 2007 HUJI-CS 30

WS-Addressing • A soap header used to – Specify the final <S: Envelope xmlns: S="http: //www. w 3. org/2003/05/soap-envelope" destination and action xmlns: wsa="http: //www. w 3. org/2004/12/addressing"> of a message <S: Header> <wsa: To>http: //Z. com/Service. URI</wsa: To> – A unique identifier for <wsa: Action>http: //Z. com/Do. Something</wsa: Action> the message <wsa: Message. ID> – The endpoint of a reply http: //example. com/Some. Unique. Message. Id. String – The endpoint of a fault </wsa: Message. ID> <wsa: Reply. To> message – The details of an <wsa: Address>http: //X. com/some. Client</wsa: Address> </wsa: Reply. To> endpoint <wsa: Fault. To> reference <wsa: Address>http: //Y. com//Error. Handler</wsa: Address> </wsa: Fault. To> </S: Header> <S: Body>  </S: Body> </S: Envelope> DBI 2007 HUJI-CS 31

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: Endpoint. Reference xmlns: wsa=". . . " xmlns: painter=". . . "> <wsa: Address>http: //housepainting. com</wsa: Address> <wsa: Reference. Properties> <painter: Service. Level>Basic Paint Job</painter: Service. Level> </wsa: Reference. Properties> </wsa: Endpoint. Reference> DBI 2007 HUJI-CS 32

Some More Details on SOAP

encoding. Style Attribute • “The SOAP encoding. Style 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. w 3. org/2002/12/soap-encoding – Other encoding rules may be used DBI 2007 HUJI-CS 34

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 p 2 p scenarios where a message can reach several servers) – must. Understand – used to indicate whether a header entry is mandatory or optional for the recipient to process – encoding. Style – as explained before DBI 2007 HUJI-CS 35

SOAP Header Element • Example: <SOAP-ENV: Header> <t: Transaction xmlns: t="some-URI" SOAP-ENV: must. Understand="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 must. Understand is set to 1, which means that the server must either understand honor the transaction request or must fail to process the message DBI 2007 HUJI-CS 36

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 DBI 2007 HUJI-CS 37

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 DBI 2007 HUJI-CS 38

SOAP Fault Codes • Version. Mismatch: Found an invalid namespace for the SOAP Envelope element • Must. Understand: An immediate child element of the Header element, with the must. Understand 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 DBI 2007 HUJI-CS 39

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> DBI 2007 HUJI-CS 40

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: Must. Understand</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 DBI 2007 HUJI-CS 41

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) DBI 2007 HUJI-CS 42

SOAP Request via HTTP POST http: //www. Hello. com/Hello. Application HTTP/1. 0 Content-Type: text/xml; charset=UTF-8 Content-Length: 587 SOAPAction: urn: hello. App <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) DBI 2007 HUJI-CS 43

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 DBI 2007 HUJI-CS 44

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. w 3. org/TR/wsdl DBI 2007 HUJI-CS 46

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 • Client uses the WSDL to properly format the SOAP request and to understand the reply DBI 2007 HUJI-CS WSDL for Service X 1 2 3 message Client 4 Service X reply 47

WSDL Can Describe • What a Web service can do • Where it resides • How to invoke it DBI 2007 HUJI-CS 48

The Structure of a WSDL Document <definition> <type> definition of a type </type> <definition> <message> definition of a message <types> </message> <port. Type> def. of operations (composed of messages) <messages> </port. Type> <binding> how to translate operations into SOAP </binding> <service> the location of the service </service> </definition> DBI 2007 HUJI-CS <port. Types> <bindings> <service> 49

<? xml version="1. 0"? > <definitions name="Currency. Exchange. Service" target. Namespace="http: //www. xmethods. net/sd/Currency. Exchange. Service. wsdl" xmlns: tns="http: //www. xmethods. net/sd/Currency. Exchange. Service. wsdl" xmlns: xsd="http: //www. w 3. org/2001/XMLSchema" xmlns: soap="http: //schemas. xmlsoap. org/wsdl/soap/" xmlns="http: //schemas. xmlsoap. org/wsdl/"> <message name="get. Rate. Request"> <part name="country 1" type="xsd: string"/> <part name="country 2" type="xsd: string"/> </message> <message name="get. Rate. Response"> <part name="Result" type="xsd: float"/> </message> <port. Type name="Currency. Exchange. Port. Type"> <operation name="get. Rate"> <input message="tns: get. Rate. Request" name="get. Rate"/> <output message="tns: get. Rate. Response" name="get. Rate. Response"/> </operation></port. Type> DBI 2007 HUJI-CS 50

<binding name="Currency. Exchange. Binding" type="tns: Currency. Exchange. Port. Type"> <soap: binding style="rpc" transport="http: //schemas. xmlsoap. org/soap/http"/> <operation name="get. Rate"> <soap: operation soap. Action=""/> <input name="get. Rate"> <soap: body use="encoded" namespace="urn: xmethods-Currency. Exchange" encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/"/> </input> <output name="get. Rate. Response"> <soap: body use="encoded" namespace="urn: xmethods-Currency. Exchange" encoding. Style="http: //schemas. xmlsoap. org/soap/encoding/"/> </output> </operation> </binding> <service name="Currency. Exchange. Service"> <documentation>Returns the exchange rate between the two currencies</documentation> <port name="Currency. Exchange. Port" binding="tns: Currency. Exchange. Binding"> <soap: address location="http: //services. xmethods. net: 80/soap"/> </port> </service> </definitions> HUJI-CS DBI 2007 51

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 DBI 2007 HUJI-CS 52

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 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 message Client 4 Service X reply DBI 2007 HUJI-CS 53

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/Story. Rss 2. 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 DBI 2007 HUJI-CS 55

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 DBI 2007 HUJI-CS 56

Mozilla’s Reader DBI 2007 HUJI-CS 57

Goggle’s Reader DBI 2007 HUJI-CS 58

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> <pub. Date>Sun, 15 Apr 2007 00: 03: 31 +0200</pub. Date> <last. Build. Date> Sun, 15 Apr 2007 00: 03: 31 +0200 </last. Build. Date> <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> DBI 2007 HUJI-CS 59

Example: Ynet Feed (cont’d) <item> <category>Updates</category> <title>Egypt pours cold water on talk of " Negotiations" </title> <description></description> <link>http: //www. ynetnews. com/articles/0, 7340, L-3387877, 00. html</link> <pub. Date>Sat, 14 Apr 2007 23: 51: 24 +0200</pub. Date> <guid>http: //www. ynetnews. com/articles/0, 7340, L-3387877, 00. html</guid> </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> <pub. Date>Sat, 14 Apr 2007 22: 30: 39 +0200</pub. Date> <guid>http: //www. ynetnews. com/articles/0, 7340, L-3387866, 00. html</guid> </item> <item> … DBI 2007 HUJI-CS 60

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 DBI 2007 HUJI-CS 61

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: – pub. Date – date of publication – comments – a link to comments about the item – category DBI 2007 HUJI-CS 62

Title, Link Description DBI 2007 HUJI-CS 63

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, …) DBI 2007 HUJI-CS 65

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 – W 3 C recommendation (Feb. 2004) DBI 2007 HUJI-CS 66

RDF Data The basic element: Triple (labeled edge) Subject RDF document: edge-labeled graph street Herzel DBI 2007 predicate Object Person#845 address #1002 city Netanya HUJI-CS postal. Code 6941 67

The XML Syntax of RDF page. html or John Smith t Crea : DC DC: Title John’s Home Page <? xml version=“ 1. 0”? > <rdf: RDF xmlns: rdf=“http: //www. w 3. 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> DBI 2007 HUJI-CS 68

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> DBI 2007 HUJI-CS 69

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 DBI 2007 HUJI-CS 70

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 DBI 2007 HUJI-CS 71

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 DBI 2007 HUJI-CS 72

Concise Introduction to RDF: Found in www. vanx. org, by Yuri Khramov, Schema. Soft

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 DBI 2007 HUJI-CS 74

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 DBI 2007 HUJI-CS 75

RDF Basics • Resources • Properties that have Values • Statement: Resource A has property B with Value C B A DBI 2007 HUJI-CS C 76

www. vanx. org/presentations/RDF Author Name Yuri Khramov DBI 2007 Mail address Yurik@schemasoft. com HUJI-CS 77

Advanced RDF • Containers: bags, sequences, alternatives • about. Each, about. Each. Prefix • Reification (higher order statements) • Namespaces and Vocabularies DBI 2007 HUJI-CS 78

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) – Net. Scape, • PRISM – publishing – Adobe, Quark, . . • <indecs> - e-business – EU companies • RDF mappings for P 3 P, PICS, … DBI 2007 HUJI-CS 79

RDF Schema • Not an XML Schema! • A “companion” specification for RDF spec • Class, Type, sub. Class. Of, • domain, range • Misc: label, comment, is. Defined. By, etc. DBI 2007 HUJI-CS 80

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? DBI 2007 HUJI-CS 81

Can we use RDF now? • IBM’s Java Central Station (uses RDF) • Mozilla’s Aurora (RDF-based) • MUZE DATAX project DBI 2007 HUJI-CS 82