Practical Applications of XML Technologies

1
Practical Applications of XML Technologies

• Foundations of Web Services
• WSDL
• Irena Mlýnková
• Martin Necaský
• Dept. of Software Engineering
• Faculty of Mathematics and Physics
• Charles University, Prague, Czech Republic

2
WSDL Basics

• Web Services Description Language
• language for describing web service interfaces
• current version 2.0
• http//www.w3.org/TR/wsdl20-primer
• editors
• David Booth, HP
• Canyang Kevin Liu, SAP Labs

3
WSDL BasicsConceptual Structure

• first approximation

Service
4
WSDL BasicsConceptual Structure

• second approximation

Interface
Implementation
5
WSDL BasicsConceptual Structure

• third approximation

Interface
Operation A
Implementation
Operation B
Operation C
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WSDL BasicsConceptual Structure

• example

Interface
ReserveFlight
Implementation
ConfirmFlight
CheckInFlight
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WSDL BasicsConceptual Structure

• WSDL allows describing of
• interfaces of web services
• where web services implementing these interfaces
  can be accessed and how
• web service
• implements interface composed of one or more
  abstract interfaces
• can be accessed at various places in different
  ways
• SOAP, HTTP,

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WSDL BasicsConceptual Structure
SOAP1.2 Endpoint
Abstract Interface ManageCustomer
Service Interface
Abstract Interface ProcessPurchase A
HTTP GET Endpoint
Abstract Interface ProcessPurchase B
HTTP POST Endpoint
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WSDL BasicsConceptual Structure
Service Description
Abstract Description
Message

Operation
Interface
Concrete Description
Binding

Service
Endpoint
10
WSDL BasicsSyntactical Structure

• root element description
• container for
• abstract definition components
• type system
• element types
• abstract interface
• element interface

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WSDL BasicsSyntactical Structure

• and for
• concrete definition components
• service description
• element service
• binding between service and interface
• element binding

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WSDL BasicsElement description
lt?xml version"1.0" encoding"utf-8"
?gt ltdescription xmlns"http//www.w3.org/ns/wsdl"gt
ltdocumentationgt ... lt/documentationgt
lt!- type system --gt lttypesgt ... lt/typesgt
lt! WSDL 2.0 components --gt ltinterfacegt ...
lt/interfacegt ltbindinggt ... lt/bindinggt
ltservicegt ... lt/servicegt lt/descriptiongt
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WSDL BasicsElement description
DEMO
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WSDL Type System
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WSDL BasicsConceptual Structure
Service Description
Abstract Description
Message

Operation
Interface
Concrete Description
Binding

Service
Endpoint
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WSDL Type SystemElement types

• describes formats for XML messages send and
  received by web service
• any XML schema language with XML syntax can be
  applied inside
• XML Schema, Relax NG, Schematron, etc.
• we (and many others) consider XML Schema
• XML Schema should be already known for you
• non-XML type system can be applied as well

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WSDL Type SystemElement types
lt?xml version"1.0" encoding"utf-8"
?gt ltdescription xmlns"http//www.w3.org/ns/wsdl"gt
ltdocumentationgt ... lt/documentationgt
lt!- type system --gt lttypesgt ... lt/typesgt
lt! WSDL 2.0 components --gt ltinterfacegt ...
lt/interfacegt ltbindinggt ... lt/bindinggt
ltservicegt ... lt/servicegt lt/descriptiongt
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WSDL Type SystemElement types
DEMO
19
WSDL Abstract Interfaces
20
WSDL BasicsConceptual Structure
Service Description
Abstract Description
Message

Operation
Interface
Concrete Description
Binding

Service
Endpoint
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WSDL Abstract Interfaces

• service description contains one or more abstract
  interfaces
• each specified by element interface
• abstract interface encapsulates set of
• supported operations
• faults reported by operations
• describes functionality only in abstract way
• no concrete details of how and where that
  functionality is offered and implemented

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WSDL Abstract InterfacesElement interface
lt?xml version"1.0" encoding"utf-8"
?gt ltdescription xmlns"http//www.w3.org/ns/wsdl"gt
ltdocumentationgt ... lt/documentationgt
lt!- type system --gt lttypesgt ... lt/typesgt
lt! WSDL 2.0 components --gt ltinterfacegt ...
lt/interfacegt ltbindinggt ... lt/bindinggt
ltservicegt ... lt/servicegt lt/descriptiongt
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WSDL Abstract InterfacesElement interface

• attributes
• name
• unique among all abstract interfaces within
  containing description
• child elements
• optional documentation
• one or more (in any order)
• fault defines fault
• operation defines operation

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WSDL Abstract InterfacesElement interface
DEMO
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WSDL Abstract InterfacesElement interface/fault

• specifies fault message that may occure during
  execution of any operation within containing
  interface
• referenced from operations within interface that
  may report that fault
• similar to ordinary messages but handled slightly
  differently
• disturbt normal message flow
• binding to underlying communication protocol
  (e.g. SOAP) may be different

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WSDL Abstract InterfacesElement interface/fault

• attributes
• required name
• unique within parent interface
• referenced from operations in same parent
  interface
• optional element
• content model of fault message
• name of element defined in type system of web
  service description

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WSDL Abstract InterfacesElement interface/fault
DEMO
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WSDL Abstract InterfacesElement
interface/operation

• operation provided by containing interface
• specifies message interaction with service via
  that operation
• set of ordinary and fault messages exchanged
  between service and other parties
• associated with message exchange pattern (MEP)
• MEP describes ordering and cardinality of
  messages within interaction via operation

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WSDL Abstract InterfacesElement
interface/operation

• attributes
• required name
• unique within parent interface
• required pattern
• xsanyURI
• identifies desired MEP for operation

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WSDL Abstract InterfacesElement
interface/operation

• attributes
• optional style
• xsanyURI
• identifies set of rules followed in defining
  operation
• e.g. "http//www.w3.org/ns/wsdl/rpc" for
  RPC-style operations

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WSDL Abstract InterfacesElement
interface/operation
DEMO
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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• define sequence and cardinality of abstract
  messages in operation
• each abstract message is represented by
  placeholder
• placeholder is identified by its role and has
  direction ("in" or "out")
• placeholders associated with specific message
  types when operation with that MEP is defined
• minimal contract
• other messages not specified by MEP may be sent
  during interaction

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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• 8 predefined MEPs in Working Draft 27 March 2006
• in-bound MEPs
• service receives first message in interaction
• In-Only, Robust In-Only, In-Out,
• In-Optional-Out
• out-bound MEPs
• service sends first message in interaction
• Out-Only, Robust Out-Only, Out-In,
• Out-Optional-In
• only three predefined MEPs in Recommendation 26
  June 2007
• In-Only, Robust In-Only, In-Out
• however, primer speaks about 8 MEPs

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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• only three predefined MEPs in Recommendation 26
  June 2007
• In-Only
• Robust In-Only
• In-Out
• however, primer of that version speaks about 8
  MEPs
• version inconsistency?

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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• In-Out
• "http//www.w3.org/ns/wsdl/in-out"
• consists of exactly two placeholders
• placeholder
• message label "In", direction "in"
• sent from some node N
• placeholder
• message label "Out", direction "out"
• sent back to N

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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• In-Only
• "http//www.w3.org/ns/wsdl/in-only"
• consists of exactly one placeholder
• placeholder
• message label "In", direction "in"
• sent from some node N

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WSDL Abstract InterfacesMore on Message Exchange
Patterns

• Robust In-Only
• "http//www.w3.org/ns/wsdl/in-only"
• consists of exactly one placeholder
• placeholder
• message label "In", direction "in"
• sent from some node N
• difference between In-Only and Robust In-Only is
  in Fault Propagation Rule applied

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WSDL Abstract InterfacesMore on Fault
Propagation Rules

• rules indicating where faults can occur in
  interaction specified by MEP
• Fault Replaces Message
• any ordinary message after the first one can be
  replaced with fault message
• fault message must have identical direction as
  replaced message and must be delivered to same
  target as replaced message
• if there is no path to target node, fault must be
  discarded
• http//www.w3.org/ns/wsdl/fault-replaces-message
• applied by In-Out MEP

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WSDL Abstract InterfacesMore on Fault
Propagation Rules

• Message Triggers Fault
• any ordinary message including the first can
  trigger fault message
• fault message must have opposite direction to the
  ordinary message and must be delivered to the
  originator of the ordinary message
• if there is no path to the originator, fault must
  be discarded
• http//www.w3.org/ns/wsdl/message-triggers-fault
• applied by Robust In-Only MEP

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WSDL Abstract InterfacesMore on Fault
Propagation Rules

• No Faults
• faults must not be propagated
• http//www.w3.org/ns/wsdl/no-faults
• applied by In-Only MEP

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WSDL Abstract InterfacesMore on Operation Styles

• specifies additional information about operation
• may define various constraints
• e.g. structural constraints on element
  declarations specifying content models of
  messages of operation
• particular operation style identified by IRI
• three predefined operation styles in WSDL 2.0
• http//www.w3.org/ns/wsdl/style/rpc
• http//www.w3.org/ns/wsdl/style/iri
• http//www.w3.org/ns/wsdl/style/multipart

42
WSDL Abstract InterfacesMore on Operation Styles

• http//www.w3.org/ns/wsdl/style/rpc
• restrictions on message content models to allow
  RPC-based communication
• http//www.w3.org/ns/wsdl/style/iri
• restrictions on message content models when HTTP
  is applied as network communication protocol
• allows serialization of messages to HTTP
  requests/response with GET/POST/PUT/DELETE HTTP
  methods
• e.g. GET does not allow HTTP message body and
  everything must be encoded into HTTP message
  header and/or HTTP request query

43
WSDL Abstract InterfacesElement
interface/operation

• ordinary messages specified by child elements
• input, output
• fault messages specified by child elements
• infault, outfault
• any number of ordinary and fault messages in any
  order
• restricted by associated MEP

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WSDL Abstract InterfacesElement
interface/operation/inputoutput

• specifies one ordinary input/output message
• attributes
• optional messageLabel
• xsNCName
• identifies role the message plays in MEP
• unique within containing operation
• predefined values "In", "Out"
• not necessary when standard MEP is applied

45
WSDL Abstract InterfacesElement
interface/operation/inputoutput

• attributes
• required element
• union of xstoken and xsQName
• specifies message content model
• values
• any any single element
• none no content
• other content is described by extension
  property that references non-XML content
  declaration
• reference to element declared in type system

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WSDL Abstract InterfacesElement
interface/operation/inputoutput
DEMO
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WSDL Abstract InterfacesElement
interface/operation/infaultoutfault

• specifies one fault input/output message
• attributes
• optional messageLabel
• xsNCName
• identifies role the message plays in MEP
• unique within containing operation
• predefined values "In", "Out"
• not necessary when standard MEP is applied

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WSDL Abstract InterfacesElement
interface/operation/infaultoutfault

• attributes
• required ref
• xsQName
• reference to abstract fault within containing
  interface
• specifies fault content model
• allows reusability of faults within the interface
  

49
WSDL Abstract InterfacesElement
interface/operation/infaultoutfault
DEMO
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WSDL Abstract InterfacesImports

• XSD element import can be used for importing
  external XML schemas into type system
• attributes namespace and schemaLocation
• WSDL element import can be used for importing
  external WSDL descriptions
• attributes namespace and schemaLocation
• attribute extends of element interface that
  allows extending external interfaces
• list of xsQName

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WSDL Abstract InterfacesImports
DEMO
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WSDL Abstract Interfaces

• "not-yet-picked" "low-hanging" fruit for
  interoperability efforts
• service can be bounded to more abstract
  interfaces
• abstract interface can be defined separately from
  web service itself

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WSDL Abstract Interfaces

• Real-world scenario 1
• two standardization organizations
• each defining own standardized abstract interface
  for processing purchase orders
• each has own type system, abstract operations and
  faults
• concrete purchase order processing web service
  supports three abstract interfaces
• one own abstract interface
• two standardized interfaces

54
WSDL Abstract Interfaces

• Real-world scenario 2
• party understands standardized abstract interface
  for purchasing flights
• it is necessary to find all services that support
  that abstract interface

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WSDL Bindings
56
WSDL BasicsConceptual Structure
Service Description
Abstract Description
Message

Operation
Interface
Concrete Description
Binding

Service
Endpoint
57
WSDL Bindings

• service description contains one or more bindings
• each specified by element binding
• binding supplies protocol and encoding details to
  given abstract interface
• implementation details needed to access service
  via that interface
• for each particular protocol there is binding
  extension
• two predefined binding extensions in WSDL 2.0
• SOAP and HTTP
• other binding extensions can be created

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WSDL Bindings

• binding is expressed with mixture of constructs
  from WSDL 2.0 namespace and binding extension
  namespace
• we will study WSDL 2.0 constructs with SOAP1.2
  binding extensions

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WSDL BindingsElement binding
lt?xml version"1.0" encoding"utf-8"
?gt ltdescription xmlns"http//www.w3.org/ns/wsdl"gt
ltdocumentationgt ... lt/documentationgt
lt!- type system --gt lttypesgt ... lt/typesgt
lt! WSDL 2.0 components --gt ltinterfacegt ...
lt/interfacegt ltbindinggt ... lt/bindinggt
ltservicegt ... lt/servicegt lt/descriptiongt
60
WSDL BindingsElement binding

• attributes
• required name
• xsNCName
• unique within containing service description
• optional interface
• xsQName
• indicates interface for which binding information
  is being specified
• if present all interface operations and faults
  must be binded inside

61
WSDL BindingsElement binding

• attributes
• required type
• xsanyURI
• specifies kind of binding details inside
• http//www.w3.org/ns/wsdl/soap for SOAP1.2
  binding
• http//www.w3.org/ns/wsdl/http for HTTP binding

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WSDL BindingsElement binding

• attributes
• optional wsoapprotocol
• xmlnswsoap"http//www.w3.org/ns/wsdl/soap"
• specifies underlying network transfer protocol
  for SOAP1.2
• http//www.w3.org/2003/05/soap/bindings/HTTP/ for
  HTTP

63
WSDL BindingsElement binding

• child elements
• optional documentation
• one or more (in any order)
• fault defines fault binding
• operation defines operation binding

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WSDL BindingsElement binding
DEMO
65
WSDL BindingsElement binding/fault

• specifies binding of abstract fault to concrete
  message format
• e.g., for SOAP
• SOAP codes and subcodes representing abstract
  fault in SOAP fault messages

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WSDL BindingsElement binding/fault

• attributes
• required ref
• xsQName
• references abstract fault for which binding
  information is being specified
• optional wsoapcode
• union of xsQName, xstoken
• maps abstract fault to specific SOAP fault with
  given code
• optional wsoapsubcodes
• union of (list of xsQName), xstoken
• specification of SOAP subcodes

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WSDL BindingsElement binding/fault
DEMO
68
WSDL BindingsElement binding/operation

• specifies binding of abstract message to concrete
  message format
• e.g., for SOAP
• binding abstract WSDL MEP to SOAP MEP

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WSDL BindingsElement binding/operation

• attributes
• required ref
• xsQName
• references abstract message for which binding
  information is being specified
• optional wsoapmep
• union of xsanyURI, xstoken
• maps abstract fault to specific SOAP fault with
  given code

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WSDL BindingsElement binding/operation
DEMO
71
WSDL BindingsDefining SOAP Header Blocks

• WSDL SOAP binding extensions allow defining
  required/optional header blocks in SOAP messages
• element header contained in elements fault, input
  and output

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WSDL BindingsElement header

• attributes
• required element
• xsQName
• element declaration within containing service
  type system
• required mustUnderstand
• xsboolean
• when true, SOAP header block must be complemented
  with SOAP mustUnderstand attribute set to true

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WSDL BindingsElement header

• attributes
• required required
• xsboolean
• specifies whether this SOAP header block is
  required or not

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WSDL BindingsElement header
DEMO
75
WSDL Services
76
WSDL BasicsConceptual Structure
Service Description
Abstract Description
Message

Operation
Interface
Concrete Description
Binding

Service
Endpoint
77
WSDL Services

• WSDL description contains one or more services
• service specifies set of endpoints where
  particular deployed implementation of bindinded
  interface is provided
• endpoints are alternate places at which service
  is provided

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WSDL ServicesElement service
lt?xml version"1.0" encoding"utf-8"
?gt ltdescription xmlns"http//www.w3.org/ns/wsdl"gt
ltdocumentationgt ... lt/documentationgt
lt!- type system --gt lttypesgt ... lt/typesgt
lt! WSDL 2.0 components --gt ltinterfacegt ...
lt/interfacegt ltbindinggt ... lt/bindinggt
ltservicegt ... lt/servicegt lt/descriptiongt
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WSDL ServicesElement service

• attributes
• required name
• xsNCName
• unique within containing service description
• required interface
• xsQName
• indicates interface implemented by this service

80
WSDL ServicesElement service

• child elements
• required endpoint

81
WSDL ServicesElement service
DEMO
82
WSDL ServicesElement endpoint

• defines details of particular service endpoint at
  which service is available
• endpoint service access point
• attributes
• required name
• xsNCName
• unique within containing service

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WSDL ServicesElement endpoint

• attributes
• required binding
• xsQName
• indicates binding of interface implemented by
  service
• optional address
• xsanyURI
• physical address where service can be accessed

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WSDL ServicesElement endpoint
DEMO
85
WSDL 2.0 vs. WSDL 1.1