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T HE US N ATIONAL V IRTUAL O BSERVATORY

T HE US N ATIONAL V IRTUAL O BSERVATORY. Building Web Services. Matthew J. Graham CACR/Caltech. Overview. WSDL Attachments Security State Asynchrony Message orientation. Design styles. Contract-last development Implement service java org.apache.axis.wsdl.Java2WSDL <interface>

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T HE US N ATIONAL V IRTUAL O BSERVATORY

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  1. THE US NATIONAL VIRTUAL OBSERVATORY Building Web Services Matthew J. Graham CACR/Caltech NVO Summer School 2006

  2. Overview • WSDL • Attachments • Security • State • Asynchrony • Message orientation NVO Summer School 2006

  3. Design styles • Contract-last development • Implement service • java org.apache.axis.wsdl.Java2WSDL <interface>  contract coupled to service implemenation’s interface • Contract-first development • Write XSD and WSDL • java org.apache.axis.wsdl.WSDL2Java -s <wsdl> • Fill in business logic NVO Summer School 2006

  4. 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) • Use WSDL 1.1 • http://www.xmethods.net NVO Summer School 2006

  5. Anatomy of a WSDL file <definitions> </definitions> <import>* - include other WSDLs <types> - define datatypes used in <message> <schema></schema>* </types> <message>* - model data exchanged <part></part>* </message> <porttype>* - describe interfaces supported for <operation>* an endpoint <input></input> - define input and output parameters <output></output> <fault></fault>* </operation> </porttype> <binding>* - formatting and representation of SOAP <operation>* message on the wire <input></input> <output></output> </operation> </binding> <service>* - identifies actual endpoint for WS <port></port>* </service> NVO Summer School 2006

  6. WSDL example • <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: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:element> • <s:element name="ComovingLineOfSightResponse”>… • <s:element minOccurs="1" maxOccurs="1" name="ComovingLineOfSightResult" type="s:float" /> • …</s:element> • </s:schema></types> • <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> • <service name="Distance"> • <port name="DistanceSoap" binding="s0:DistanceSoap"> • <soap:address location="http://voservices.net/Cosmology/ws_v1_0/Distance.asmx" /> • </port> • </service> • </definitions> NVO Summer School 2006

  7. What about the binding? <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> NVO Summer School 2006

  8. Binding attributes • Style (representation on the wire) • rpc: the endpoint treats child elements in the body as XML representation of method call (SOAP 1.1, sec. 7) • document: the body can contain arbitrary XML • Use (how data is serialized across the wire) • encoded: rules in a URL specified by encodingStyle attribute • literal: rules specified by XML schema NVO Summer School 2006

  9. 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 2006

  10. 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 2006

  11. 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 2006

  12. Which flavour to use? • Doc style can pass entire transaction as an XML document (state) • Doc style not constrained by RPC-oriented encoding • Doc style can be validated at call time • Processing overhead in encoding payloads with RPC • Doc style can use low memory parsers such as SAX and StAX • RPC’s natural tendency to expose programming language object structures  doc/literal wrapped (95%) NVO Summer School 2006

  13. Why not doc/literal wrapped? - I rpc/literal doc/literal doc/literal wrapped • <message name=“Request”> • <part name=“x” type=“xs:int”/> • </message> • <types> • <schema> • <element name=“xElement” • type=“xs:int”/> • </schema> • </types> • <message name=“Request”> • <part name=“x” element=“xElement”/> • </message> • <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> • <portType name=“foo”> • <operation name=“method”> • <input message=“Request”/> • </operation> • </portType> • <soap:envelope> • <soap:body> • <method> • <x>5</x> • </method> • </soap:body> • </soap:envelope> • <soap:envelope> • <soap:body> • <xElement>5</xElement> • </soap:body> • </soap:envelope> • <soap:envelope> • <soap:body> • <method> • <x>5</x> • </method>> • </soap:body> • </soap:envelope> NVO Summer School 2006

  14. Why not doc/literal wrapped? - II • Overloaded operations: public void myMethod (int x, float y); public void myMethod (int x); • Number of parameters: public void someOtherMethod(int x, float y); • Data graphs: <complexType name=“Node”> <sequence> <element name=“name” type=“string”/> <element name=“left” type=“Node”/> <element name=“right” type=“Node”/> </sequence> </complexType> RPC/encoding: <A> Literal: <A> <name>A</name> <name>A</name> <left href=“9999”/> <left> <right href=“9999”/> <name>B</name> </A> </left> <B id=“9999”> <right> <name>B</name> <name>B</name> </B> </right> </A> A Left Right B Left Right NVO Summer School 2006

  15. 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 2006

  16. WS-* • WS-Semantics • WS-Topic • WS-Transaction • WS-Transaction Management • WS-Transfer • WS-Trust • ASAP • ebXML • MTOM • SAML • SOAP • SwA • UBL • UDDI • WSDL • XACML • XML Encryption • XML Signature • XKMS • WS-I Basic Profile • WS-I Basic Security Profile • WS-Manageability • WS-Management • WS-MetadataExchange • WS-Notification • WS-Policy • WS-PolicyAssertions • WS-PolicyAttachment • WS-PolicyFramework • WS-Polling • WS-Provisioning • WS-Reliability • WS-ReliableMessaging • WS-RemotePortals • WS-ResourceFramework • WS-ResourceLifetime • WS-ResourceProperties • WS-Routing • WS-SecureConversation • WS-Security • WS-SecurityPolicy • WS-Addressing • WS-AtomicTransaction • WS-Attachments • WS-BaseNotification • WS-BPEL • WS-BrokeredNotification • WS-BusinessActivity • WS-CAF • WS-Choreography • WS-CDL • WS-Context • WS-Coordination • WS-CoordinationFramework • WS-Discovery • WS-DistributedManagement • WS-Enumeration • WS-Eventing • WS-ExperienceLanguage • WS-Federation • WS-GAF • WS-Inspection • WSIL NVO Summer School 2006

  17. Attachments: opaque data • “By value” • XML representation or • use xs:hexBinary or xs:base64Binary within the body • data expansion by a factor of ~1.33 - 4 • anything within SOAP body gets parsed • processing costs of encoding/decoding • “By reference” • attach pure binary data as external unparsed entity outside SOAP message • use reference URI within the body NVO Summer School 2006

  18. Reference solutions • SwA (SOAP with Attachments) • Multipart MIME message: SOAP (0), data (1-n) • Use Content-Id as reference in body • Lack of length header on message sections • No recommendation just W3C Note • DIME (Direct Internet Message Encapsulation) • Uses faster and more efficient binary encoding • No standard, disowned by Microsoft • Both introduce a data structure outside realm of XML data model: no rules to specify how attachment content related to SOAP envelope so incompatible with WS-* NVO Summer School 2006

  19. MTOM • Message Transmission Optimization Mechanism • Uses MIME - backwards compatible with SwA • Uses XOP:Include as reference mechanism (XOP = XML Binary Optimized Packaging) • Conceptually binary data is base64-encoded in SOAP XML document  compatible with WS-* • Implementations: • Axis2 (http://ws.apache.org/axis2) • Xfire (http://xfire.codehaus.org) • WSE 3.0 (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwse/html/newwse3.asp) NVO Summer School 2006

  20. Security • Transport level (https) • Message level: • End-to-end: allows for unlimited intermediaries • Data origin authentication • Different types of security tokens/credentials: • unsigned (username/password) • binary (X.509 certificate) • XML (SAML token) • Multiple credentials NVO Summer School 2006

  21. WS-Security • OASIS standard (http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wss)) • Security token validation (authentication): • validate authentication assertions made by principals • Message integrity (signing): • verify message origin • validate encryption keys • confirm security token claims • Message confidentiality (encryption) • Introduces extra XML into SOAP header NVO Summer School 2006

  22. WSS Implementations • Java: • WSS4J (http://ws.apache.org/wss4j) used by Axis2/XFire • C#: • WSE 2.0 (http://msdn.microsoft.com/webservices/webservices/building/wse/default.aspx) • WSRF.Net (http://www.cs.virginia.edu/~gsw2c/wsrf.net.html) • Perl : • WSRF::Lite (http://www.sve.man.ac.uk/Research/AtoZ/ILCT) • Python: • pyGridWare (http://dsd.lbl.gov/gtg/projects/pyGridWare/) NVO Summer School 2006

  23. State • Stateless is good: • In case of failure, just restart without concern of previous interactions (reliability) • New service instances can be created/destroyed in response to system load (scalability) • How to handle state? • Separate web service and state information (resource) • Identify resource with a unique key • Use message exchanges with the service to interact with the resource (manipulate state) NVO Summer School 2006

  24. WS-Resource • An entity composed of a web service and a stateful resource • The address is called an endpoint reference (WS-Addressing) • ACID: • Updates made in all-or-nothing fashion (atomicity) • Consistent state even after failure (consistency) • Updates isolated within a given work unit (isolation) • Permanence of updates (durability) NVO Summer School 2006

  25. WS-RF: the nuts and bolts • WSDL for a stateful service: <definitions> <import>* <types> <xs:schema> <xs:element name=“StatefulResourceProperties”>…</xs:element> <xs:schema> <types> <porttype wsdlpp:extends=“…” wsrp:ResourceProperties=“tns:StatefulResourceProperties”> • Implementations: • Java: GT4 (htttp://www.globus.org); Apache WSRF (http://ws.apache.org/wsrf) • .NET: WSRF.Net (http://www.cs.virginia.edu/~gsw2c/wsrf.net.html) • Python: pyGridWare (http://dsd.lbl.gov/gtg/projects/pyGridWare/) • Perl: WSRF::Lite (http://www.sve.man.ac.uk/Research/AtoZ/ILCT) NVO Summer School 2006

  26. Asynchrony • Real world is asynchronous • No current standards for asynchronous services but most promising is OASIS ASAP (http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=asap) • Toolkits exist which facilitate asynchronous activities: • WS-RF (see above) • Axis2 (http://ws.apache.org/axis2) • JMS (http://java.sun.com/products/jms) / Caffeine (http://caffeine.berlios.de/site/) • WSIF (http://www.apache.org/wsif) NVO Summer School 2006

  27. Messaging operations • WSDL 1.1 defines four types of messaging operation that an endpoint can support: • One-way: endpoint receives a message • Request/response: endpoint receives a message and sends a correlated message • Solicit/response: endpoint sends a message and receives a correlated message • Notification: endpoint sends a message • One-way/two-way transport behaviour NVO Summer School 2006

  28. Patterns for asynchrony (I) • Fire and Forget: • Request/response (Transport timeout) C S C S C S NVO Summer School 2006

  29. Patterns for asynchrony (II) • Polling: • Callback: C S C S NVO Summer School 2006

  30. WS-Addressing • No standard SOAP way to specify: • where a message is going • how to return a response • where to report an error • WS-Addressing provides: • To • ReplyTo • FaultsTo • Anonymous • MessageId / RelatesTo • Standard for including service-specific attributes NVO Summer School 2006

  31. What’s wrong with WSDL (for SOAP)? • Focuses on interface abstraction to describe services (‘RPC mindset’) • Limited modelling of interaction patterns (no more than 2 message exchanges) • No choreographical information (x  y  z) • Difficult to describe infrastructure protocols that use SOAP headers • Technologies that use WSDL as a basis tend to be more verbose and complex than necessary NVO Summer School 2006

  32. MEST (MESsage Transfer) • Messaging: • No notion of client/server: just peers • Largely time independent: messages delivered when peer is available • Messages can be duplicated and delivered to multiple peers • Messages and services are first class abstractions (no interfaces, data and operations) • SSDL (http://www.ssdl.org) • Indigo: dual contracts are beyond WSDL NVO Summer School 2006

  33. SSDL • SOAP is the messaging vector over arbitrary transport (and transfer) protocols • WS-Addressing used for embedding addressing information within SOAP envelopes and binding those addresses onto underlying transport protocols • XML Infoset is the underlying component model • Use Xinclude for contract modularization • Promotes protocol framework extensibility NVO Summer School 2006

  34. SSDL structure • Schemas • XML Schemas • Messages • SOAP documents • Protocols (how messages relate to each other) • MEP (WSDL 2.0) • Communicating Sequential Processes • Rules (uses preconditions on send and receive events) • Sequential Constraints • Endpoints • WS-Addressing Endpoint Reference NVO Summer School 2006

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