T Network Application Frameworks and XML Web Services and WSDL Sasu Tarkoma Based on slides by Pekka Nikander

Contents n Short review of XML & related specs n Web Services u Driving forces u Architecture & protocol stack n WSDL 1.1 u WSDL document elements u Mapping SOAP to WSDL n WSDL 2.0 n Implementations n Towards the Semantic Web n Summary

XML n XML (eXtensible Markup Language) is a framework for defining markup languages n Standardized by W3C n Idea: to separate syntax from semantics, custom markup, internationalization, platform independence n XML Document: prolog, elements, attributes, entity references, comments n Validated using DTD or schema n Two things: well-formedness and validity

Related standards n Namespaces u Modular document definition, multiple inheritance, collision avoidance n XPath / XQuery u Navigation and query of parts of the document n XML linking language (Xlink) n XML Schema u definition of document structure and custom data types n XSLT u Transformation of documents

Namespaces n Many documents can have identical elements that denote different things u Namespaces are the XML way to classify elements u A qualified name is a name subject to namespace interpretation n W3C Recommendation n In general, a namespace is just a tag u An arbitrary string u Does not need to be a URI n A common practice to store a schema / WSDL into the place referenced by the URI u Semantics depends on the specific platform u Some XML validators use these

Example namespace <!-- the 'price' element's namespace is --> <edi:price xmlns:edi=' units='Euro'>32.18

About Schemas n XML language for describing and constraining the content of XML documents n A W3C Recommendation n Used to specify u The allowed structure of an XML document u The allowed data types contained in XML documents n XML Schema documents are XML documents n Schema document: schema element and element, attribute, and type definitions + annotations

Driving forces I n Universal data access / representation u Independent of OS, programming language, network protocol, … n Move from human-centric to application- centric web u Applications converse with each other and use machine-related information published on the web u Application-areas: package tracking, card verification, shopping bots, single sign-on, calendar, ,...

Driving forces II n Making Web a programming interface u We have had servlets, CGI, CORBA for years u Idea is to standardise languages and protocols to have better integration n Make service composition possible u Faster project throughput u Cope with heterogeneity n Deferred binding u Many levels of deference

A Basic Web Service Computer A Language: C++ OS: W2000 Computer A Language: C++ OS: W2000 Computer B Language: Java OS: Linux Computer B Language: Java OS: Linux XML Independent of language, OS, network protocols

Additional properties n A web service should be self-describing u Interface is published with the implementation u Minimum interface is human readable description u The interface can also be written in a common XML grammar (WSDL) n A web-service should be discoverable u The web service is published u Interested parties can find it n Not mandatory but desirable properties

Standardization n W3C Web Services u XML Protocol Working Group F SOAP u Web Services Addressing Working Group u Web Services Choreography Working Group u Web Services Description Working Group F WSDL n OASIS u E-business standards, UDDI n WS-I (Web Service Interoperability Org.) u Binding profiles,..

Web Service Architecture n The three major roles in web services u Service provider F Provider of the WS u Service Requestor F Any consumer / client u Service Registry F logically centralized directory of services n A protocol stack is needed to support these roles

XML Messaging n Several alternatives for XML messaging u XML Remote Procedure calls (XML-RPC) u SOAP u Regular XML transported over HTTP XML-RPCSOAP HTTP POST/GET

SOAP Version 1.2 n The definition of the XML-based information for exchanging structured and typed information between peers n A SOAP message is formally specified as an XML Infoset n Infosets can have different on-the-wire representations, one common example of which is as an XML 1.0 document. n A stateless, one-way message exchange paradigm n Applications can create more complex interaction patterns u request/response, request/multiple responses

Web Services Protocol Stack n Message Transport u Responsible for transporting messages u HTTP, BEEP n XML Messaging u Responsible for encoding messages in common XML format u XML-RPC, SOAP n Service Description u Responsible for describing an interface to a specific web service u WSDL n Service discovery u Responsible for service discovery and search u UDDI

WS Protocol Stack Transport: HTTP, FTP, BEEP, SMTP, JMS XML Messaging: SOAP, XML-RPC, XML Description: WSDL Discovery: UDDI

Main components today n XML data representation u XML Schema Definitions (xsd) for types u XML Namespaces for unambiguity n SOAP u Basic transport (XML messaging) u Sync / async communication and RPC n WSDL u Description of (SOAP) services n UDDI u Service registry

Example WS layering Transport: HTTP(S), SMTP, JMS,.. XML processor SOAP processor Serialization / deserialization (java to XML mapping) Service container J2EE integration Management services:Admin, UDDI, depl., auditing

How it could work n 1. A standard body creates a WSDL definition n 2. A service programmer implements a service according to the WSDL definition n 3. A client programmer implements a client according to the WSDL definition n 4. A service provider deploys the sevice, and registers it into UDDI n 5. A client program pulls WSDL from UDDI, checks conformance, an uses SOAP for access

2. Creating server application n Pull WSDL definition from somewhere (UDDI) u Only use high-level WSDL, no bindings yet n Generate platform specific skeleton code using automated tools n Write the actual program code

3. Creating client application n Pull WSDL definition from somewhere (UDDI) u Use only high-level WSDL, no bindings yet n Generate platform specific stub code using automated tools n Write the actual program code

4. Deploying the service UDDI WSDL document WSDL document WSDL portType WSDL portType WSDL binding WSDL binding WS service SOAP proc. Transport

5. Using a service UDDI WSDL portType WSDL portType WSDL binding WSDL binding WS service SOAP proc. Transport WSDL document WSDL document

About invocation mechanisms n WS does not define an invocation mechanism n Alternatives u Microsoft.NET framework u Java-based framework F JAVA API for WSDL (JWSDL) F JAX-RPC F Java API for XML registries (JAXR) F Apache Axis F...

WSDL with Java Services WSDL document JAXR UDDI Publish firewall WS requester Business partner or other system SOAP RQ Bind SOAP RQ 1. WSDL is published to UDDI 2. Look up WS 3. Retrieve WSDL description 4. Call WS JAXR= Java API for XML Registries

What is WSDL? n WSDL: Web Service Description Language n An XML language used to describe and locate web services u location of web service u methods that are available u data type information and XML messages n Commonly used to describe SOAP-based services n W3C standard (work in progress) u Initial input: WSDL 1.1 as W3C Note u Current version 2.0 (last call) u Some differences between 1.1 and 2.0 n WSDL 1.1 in WS-I Basic Profile 1.0 and 1.1.

WSDL Document Elements (v.1.1.) n - data type definitions n - Abstract definition of the data being transmitted n - A set of abstract operations n - Concrete protocol an data format specifications for the operations and messages defined by a particular portType n - An address for binding n - Aggregate a set of related ports

WSDL Overview : ROOT WSDL element : The data types that are used : What messages are transmitted? : The supported operations : The binding to concrete protocols : Reference to actual location

A WSDL Document n A WSDL document contains two parts n Abstract part u Interfaces, types, messages n Concrete part u Binding to conrete protocol and encoding

31 of 20 Mapping SOAP to WSDL

Message Styles n The WSDL 1.1 specification defines two SOAP message styles n Determined in binding n Document u contains one or more child elements called parts u There are no SOAP formatting rules for what the contains u preferred, loose coupling, easy validation n RPC u contains an element with the name of the method or remote procedure being invoked u This element in turn contains an element for each parameter of the procedure u less popular today, tighter coupling

The main structure (v.1.1) XML Schema types.. a set of operations Communication protocols A list of binding and ports

Types n define data types used in message declaration n For platform neutrality, WSDL uses XML Schema syntax to define data u XML Schema must be supported by any vendor of WSDL conformant products u Other kinds of type definitions also possible F Possible interoperability issues u If the service uses only XML Schema built-in simple types, such as strings and integers, the types element is not required

<schema targetNameSpace=" xmlns:xsd=" <element name="tickerSymbol" type="xsd:string" minOccur="1" maxOccur="10"/> </element Specifies that the child elements can appear in any order. Each child element can occur 0 or 1 time Namespace definitions Only one of the elements is allowed

Corresponding XML instance ABC 1234

WSDL Messages n The element defines the data elements of an operation u the name of the message u contains zero or more message part elements n The parts can be compared to the parameters of a function call in a traditional programming language n All parts are typed by an XML Schema type n V.2.0 changes: message element is not used, replaced by patterns

WSDL Ports n The element is the most important WSDL element n The operations that can be performed, the messages that are involved n A defines the connection point to a web service, an instance of n It can be compared to a function library (or a module, or a class) in a programming language

Example

Operation Types (v.1.1) n One-Way: The operation can receive a message but will not return a response n Request-Response: The operation can receive a request and will return a response n Solicit-Response: The endpoint sends an output message and then receives an input message. n Notification: The operation can send a message but will not wait for a response n v.2.0 changes: abstract message patterns

One way and Notification Example

Bindings n The element defines u The message format and u protocol details

Example <binding name="StockQuoteSoapBinding" type="tns:StockQuotePortType"> <soap:binding style="document" transport=" <soap:operation soapAction=" Must use for document-style. For RPC style type encoding info is eliminated. Difference is that for RPCliteral params have schemas but the whole body does not. Specifies that the SOAPAction HTTP header be used for identifying the service RPC or document. RPC has a wrapper for func. Names & params

Service n Real-life address of the service u A URL containing a DNS name <port name="StockQuotePort" binding="tns:StockQuoteBinding">

Putting it together Source:

WSDL 2.0 n 3 specifications n Part 1: Core u Abstract interfaces, independent of protocol and encoding n Part 2: Message Exchange Patterns u Predefined types of interactions n Part 3: Bindings u SOAP and HTTP/MIME binding n Lot’s of changes from 1.1

Changes from 1.1 to 2.0 n Adding further semantics to the description language. n Removal of message constructs. These are specified using the XML schema type system in the types element. n No support for operator overloading. n PortTypes renamed to interfaces. Support for interface inheritance is achieved by using the extends attribute in the interface element. n Ports renamed to endpoints. n Abstracted message patterns

WSDL 2.0 Conceptual Model Source:

WSDL 2.0 Component Model Source: First%20Look%20at%20WSDL%202.0.article

Message Exchange Patterns MEP in-only robust-in-only In-out out-only robust-only-out out-in out-optional-in Description Single input message Output followed by an opt. Input Input message + output message Single output message Output followed by input msg Single input message Fault No Trigger Replace No Trigger Replace Trigger in-optional-outInput followed by an opt. OutputTrigger

Implementations n Microsoft.NET u SOAP 1.1, WSDL 1.1 n Java API for XML-based RPC (JAX-RPC) u SOAP 1.1, WSDL 1.1 n Java API for XML Registries (JAXR) n Apache Axis u Tools for automatically creating WSDL to/from Java u SOAP 1.1 and 1.2, WSDL 1.1, JAX-RPC 1.0 n IBM Websphere, BEA Web Logic, SAP NetWeaver, …

What about semantics? n In many cases, applications (or agents) need to deduce and infer about information n In order to make this possible u Semantic information is needed n Tim Berners Lee, the inventor of the WWW, has proposed the Semantic Web u Application centric u Semantic and logic layers

Semantic Web layers UnicodeURI XML+Namespaces+XML Schema Trust Proof Rules Logic Data Ontology vocabulary Data RDF + RDF Schema Doc Dig. Sig.

Summary n Deferred binding, using Web, composition n Some details and conventions still unclear u Possible interoperability issues n Parts hard to understand u Namespaces u Schemas u Differences between versions u Document vs. RPC SOAP style F Also literal vs. encoded F More about this next week