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Introduction to Web Services Technology

T HE US N ATIONAL V IRTUAL O BSERVATORY. Introduction to Web Services Technology. Matthew J. Graham CACR/Caltech. Overview. SOA SOAP, WSDL and UDDI Infrastructures: AXIS, .Net (Mono), Python, Perl, PHP Invocation Interoperability

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Introduction to Web Services Technology

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  1. THE US NATIONAL VIRTUAL OBSERVATORY Introduction to Web Services Technology Matthew J. Graham CACR/Caltech NVO Summer School

  2. Overview • SOA • SOAP, WSDL and UDDI • Infrastructures: AXIS, .Net (Mono), Python, Perl, PHP • Invocation • Interoperability • Emerging topics: attachments, state, security, asynchronous NVO Summer School

  3. Service Oriented Astronomy • An application architecture within which all functions are defined as independent services with well-defined invocable interfaces which can be called in defined sequences to form scientific processes. • Web Services are animplementation NVO Summer School

  4. Technological challenges • WS technologies need to address four basic challenges: • Service Description • Service Implementation • Service Publishing, Discovery and Binding • Service Invocation and Execution NVO Summer School

  5. What’s wrong with HTTP GET? • “Things should be made as simple as possible, but no simpler” - Albert Einstein • Highly scalable, predominantly read-only data • REST (Representational State Transfer) • Amazon.com: • has both REST and SOAP APIs • 85% of requests are REST • REST response is 6 times faster than SOAP NVO Summer School

  6. Why is SOAP better? • Send and receive complex datatypes to invoke a particular method not just key-value pairs • Security - not URI parameters • Guaranteed or exact execution • Binds to other protocols NVO Summer School

  7. What is SOAP? • Simple Object Access Protocol • An XML-based communication protocol and encoding format for exchanging structured information in a decentralized, distributed environment • W3C specification (http://www.w3.org/TR/soap) NVO Summer School

  8. Anatomy of a SOAP message • An envelope to encapsulate data which defines formatting conventions for describing the message contents and routing directions • A request/response message exchange pattern (RPC mechanism) • A transport or binding protocol • Data encoding rules for describing the mapping of application-defined datatypes into an XML tag-based representation NVO Summer School

  9. SOAP example Request: <soap:Envelope xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xmlns:xsd=http://www.w3.org/2001/XMLSchema xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ComovingLineOfSight xmlns="http://skyservice.pha.jhu.edu"> <z>float</z> <hubble>float</hubble> <omega>float</omega> <lambda>float</lambda> </ComovingLineOfSight> </soap:Body> </soap:Envelope> Response: <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ComovingLineOfSightResponse xmlns="http://skyservice.pha.jhu.edu"> <ComovingLineOfSightResult>float</ComovingLineOfSightResult> </ComovingLineOfSightResponse> </soap:Body> </soap:Envelope> NVO Summer School

  10. What is WSDL? • Web Services Description Language • An XML grammar for describing a web service as a collection of endpoints capable of exchanging messages in a particular fashion • W3C specification (http://www.w3.org/TR/wsdl) NVO Summer School

  11. Anatomy of a WSDL file - include other WSDLS - define datatypes used in <message> elements - model data exchanged - a subset of operations supported for an endpoint - define input and output messages - concrete protocol and data format specification for a <portType> element - identifies actual endpoint for WS <definitions> <import>* <types> <schema></schema>* </types> <message>* <part></part>* </message> <portType>* <operation>* <input></input> <output></output> <fault></fault>* </operation> </portType> <binding>* <operation>* <input></input> <output></output> </operation> </binding> <service>* <port></port>* </service> </definitions> NVO Summer School

  12. WSDL example (I) <?xml version="1.0" encoding="utf-8"?> <definitions xmlns:http="http://schemas.xmlsoap.org/wsdl/http/" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:s="http://www.w3.org/2001/XMLSchema" xmlns:s0="http://skyservice.pha.jhu.edu" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" targetNamespace="http://skyservice.pha.jhu.edu" xmlns="http://schemas.xmlsoap.org/wsdl/"> <types> <s:schema elementFormDefault="qualified" targetNamespace="http://skyservice.pha.jhu.edu"> <s:element name="ComovingLineOfSight"> <s:complexType> <s:sequence> <s:element minOccurs="1" maxOccurs="1" name="z" type="s:float" /> <s:element minOccurs="1" maxOccurs="1" name="hubble" type="s:float" /> <s:element minOccurs="1" maxOccurs="1" name="omega" type="s:float" /> <s:element minOccurs="1" maxOccurs="1" name="lambda" type="s:float" /> </s:sequence> </s:complexType> </s:element> <s:element name="ComovingLineOfSightResponse"> <s:complexType> <s:sequence> <s:element minOccurs="1" maxOccurs="1" name="ComovingLineOfSightResult" type="s:float" /> </s:sequence> </s:complexType> </s:element> </s:schema> </types> NVO Summer School

  13. WSDL example (II) <message name="ComovingLineOfSightSoapIn"> <part name="parameters" element="s0:ComovingLineOfSight" /> </message> <message name="ComovingLineOfSightSoapOut"> <part name="parameters" element="s0:ComovingLineOfSightResponse" /> </message> <portType name="DistanceSoap"> <operation name="ComovingLineOfSight"> <documentation>Return the comoving line of sight distance...</documentation> <input message="s0:ComovingLineOfSightSoapIn" /> <output message="s0:ComovingLineOfSightSoapOut" /> </operation> </portType> <binding name="DistanceSoap" type="s0:DistanceSoap"> <soap:binding transport="http://schemas.xmlsoap.org/soap/http" style="document" /> <operation name="ComovingLineOfSight”> <soap:operation soapAction="http://skyservice.pha.jhu.edu/ComovingLineOfSight" style="document" /> <input> <soap:body use="literal" /> </input> <output> <soap:body use="literal" /> </output> </operation> </binding> <service name="Distance"> <documentation>...</documentation> <port name="DistanceSoap" binding="s0:DistanceSoap"> <soap:address location="http://voservices.net/Cosmology/ws_v1_0/Distance.asmx" /> </port> </service> </definitions> NVO Summer School

  14. WSDL binding flavours (I) RPC Document • <message name=“Request”> • <part name=“x” type=“xs:int”/> • </message> • <message name=“empty”/> • <portType name=“foo”> • <operation name=“method”> • <input message=“Request”/> • <output message=“empty”/> • </operation> • </portType> • <types> • <schema> • <element name=“xElement” type=“xs:int”/> • </schema> • </types> • <message name=“Request”> • <part name=“x” element=“xElement”/> • </message> • <message name=“empty”/> • <portType name=“foo”> • <operation name=“method”> • <input message=“Request”/> • <output message=“empty”/> • </operation> • </portType> Literal • <message name=“Request”> • <part name=“x” type=“xs:int”/> • </message> • <message name=“empty”/> • <portType name=“foo”> • <operation name=“method”> • <input message=“Request”/> • <output message=“empty”/> • </operation> • </portType> Encoding NVO Summer School

  15. WSDL binding flavours (II) RPC Document • <soap:envelope> • <soap:body> • <method> • <x>5</x> • </method> • </soap:body> • </soap:envelope> • <soap:envelope> • <soap:body> • <xElement>5</xElement> • </soap:body> • </soap:envelope> Literal • <soap:envelope> • <soap:body> • <method> • <x xsi:type=“xs:int”>5</x> • </method> • </soap:body> • </soap:envelope> Encoding NVO Summer School

  16. WSDL binding flavours (III) Document/literal wrapped • <types> • <schema> • <element name=“method”> • <complexType> • <sequence> • <element name=“x” type=“xs:int”/> • </sequence> • </complexType> • </element> • </schema> • </types> • <message name=“Request”> • <part name=“parameters” element=“method”/> • </message> • <message name=“empty”/> • <portType name=“foo”> • <operation name=“method”> • <input message=“Request”/> • <output message=“empty”/> • </operation> • </portType • <soap:envelope> • <soap:body> • <method> • <x>5</x> • </method>> • </soap:body> • </soap:envelope> NVO Summer School

  17. UDDI • Universal Description, Discovery and Integration • A platform-independent, open framework for publishing and discovering information about web services • OASIS specification (http://www.uddi.org) NVO Summer School

  18. What do I need? • SOAP library • WSDL parser • Client and server stub code generator • Service container • (UDDI library) NVO Summer School

  19. What’s available? • Java (http://www.javaskyline.com/webservices): • Axis (http://ws.apache.org/axis) • Globus (http://www.globus.org) • C#: • .Net; Mono (http://www.go-mono.com) • OGSI.NET / WSRF.NET (http://www.cs.virginia.edu/~gsw2c/wsrf.net.html) • Perl: • SOAP::Lite (http://www.soaplite.com) • OGSI::Lite / WSRF::Lite (http://www.sve.man.ac.uk/Research/AtoZ/ILCT) • Python: • SOAPpy / ZSI (http://pywebsvcs.sourceforge.net) • Twisted (http://www.twistedmatrix.com/products/twisted) • PyGlobus/PyGridWare • PHP • NuSOAP (http://dietrich.ganx4.com/nusoap) • XForms (http://www.w3.org/MarkUp/Forms) NVO Summer School

  20. Client Invocation Models • Static: use generated stubs • Dynamic: • no generated code • a proxy dynamically generates a class at runtime that conforms to a particular interface, proxying all invocations to a single ‘generic’ method • standard Java : use javax.xml.rpc.Service.getPort() and createCall() • .Net : use RealProxy class (must extend ContextBound) or Reflection.Emit NVO Summer School

  21. Interoperability • Suitable for and capable of being implemented in a neutral manner on multiple operating systems and in multiple programming languages • Not all web services are interoperable! • Web Services Interoperability Organisation (http://www.ws-i.org) • WS-I Testing Tools NVO Summer School

  22. Emerging technologies • Attachments: • DIME vs. MTOM (http://www.w3.org/TR/soap12-mtom) • Security: • WS-Security (http://www-106.ibm.com/developerworks/webservices/library/ws-secure) • WSS4J? • State: • WSRF (http://www.globus.org/wsrf) • Asynchronous: • WS-CAF (http://www.arjuna.com/standards/ws-caf”) • WSRF NVO Summer School

  23. Conclusions • Make sure a web service is the best solution to an application requirement • Focus on the WSDL • Use your favourite language and platform • Interoperability is a great idea • Be aware of emerging and converging technologies NVO Summer School

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