Web Services Overview
Francisco Curbera
IBM T.J. Watson Research Center
Livermore July 25 2001
Outline
1. Why Web Services?
2. The Web Services Computing Stack.
3. Summary.
Livermore July 25 2001
1. Why Web Services?
Livermore July 25 2001
Today’s Web
Web designed for application to human interactions
Served very well its purpose:
Information sharing: a distributed content library.
Enabled B2C e-commerce.
Non-automated B2B interactions.
How did it happen?
Built on very few standards: http + html
Shallow interaction model: very few assumptions made about
computing platforms.
Result was ubiquity.
Livermore July 25 2001
What’s next?
The Web is everywhere. There is a lot more we can do!
E-marketplaces.
Open, automated B2B e-commerce.
Business process integration on the Web.
Resource sharing, distributed computing.
Current approach is ad-hoc on top of existing standards.
e.g., application-to-application interactions with HTML forms.
Goal:
enabling systematic application-to-application
interaction on the Web.
Livermore July 25 2001
Web Services
“Web services” is an effort to build a
distributed computing platform for the
Web.
Yet another one!
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Designing Web Services I
Goals
Enable universal interoperability.
Widespread adoption, ubiquity: fast!
Compare with the good but still limited adoption of the
OMG’s OMA.
Enable (Internet scale) dynamic binding.
Support a service oriented architecture (SOA).
Efficiently support both open (Web) and more
constrained environments.
Livermore July 25 2001
Designing Web Services II
Requirements
Based on standards. Pervasive support is critical.
Minimal amount of required infrastructure is
assumed.
Only a minimal set of standards must be implemented.
Very low level of application integration is expected.
But may be increased in a flexible way.
Focuses on messages and documents, not on APIs.
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Web Services Model
Web service applications are
encapsulated, loosely coupled Web
“components” that can bind
dynamically to each other
Livermore July 25 2001
2. The Web Services Framework
Livermore July 25 2001
Web Services Framework
Framework can be described in terms of
What goes “on the wire”:
Formats and protocols.
What describes what goes on the wire:
Description languages.
What allows us to find these descriptions:
Discovery of services.
Livermore July 25 2001
XML Messaging: SOAP
SOAP 1.1 defined:
An XML envelope for XML messaging,
Headers + body
An HTTP binding for SOAP messaging.
SOAP is “transport independent”.
A convention for doing RPC.
An XML serialization format for structured data
SOAP Attachments adds
How to carry and reference data attachments using in
a MIME envelope and a SOAP envelope.
Livermore July 25 2001
The SOAP Envelope
<SOAP-ENV:Envelope
xmlns="http://schemas.xmlsoap.org/soap/envelope/">
< SOAP-ENV:Header>
...
</ SOAP-ENV:Header>
< SOAP-ENV:Body>
...
</ SOAP-ENV:Body>
...
</ SOAP-ENV: Envelope>
Livermore July 25 2001
What goes on the wire
Internet-scale integration needs
a lingua-franca Context
Context
XML messaging protocol
Transactions
Transactions
over HTTP: SOAP
Routing
Routing
Intra-enterprise integration
needs to allow alternates: Reliability
Reliability
CORBA, RMI
Messaging Security
Security
In-memory method calls
Attachments
Attachments
W3C
SOAP
SOAP
Livermore July 25 2001
Descriptions: Meta-data
Integration requires Agreements
Agreements
interoperable machine- Flows
Flows and
and
WSFL
understandable descriptions Composition
Composition
Public
Public Flows
Flows
Enables dynamic, delayed
binding of components. Service
Service QoS
QoS
Language extensibility provides Service
Service
WSDL
support for different levels of
application integration. Interface
Interface
XML
XML Schema
Schema
Livermore July 25 2001
Web Services Description Language
Provides functional description of network services:
IDL description
Protocol and deployment details
Platform independent description.
Extensible language.
A short history:
WSDL v1.0, 9/2000
WSDL v1.1 submitted to W3C 3/2001.
A de facto industry standard.
Livermore July 25 2001
WSDL Structure
Service
portType
Abstract definition of a Port Port
(e.g. http://host/svc)
service (set of operations) Binding
(e.g. SOAP)
Binding
Multiple bindings per
portType:
portType
How to access it
SOAP, JMS, direct call
operation(s)
Ports inMesage outMessage
Where to access it
Abstract interface
Livermore July 25 2001
Using WSDL
1. As extended IDL: WSDL allows tools to generate
compatible client and server stubs.
Tool support for top-down, bottom-up and “meet in the
middle” development.
2. Allows industries to define standardized service
interfaces.
3. Allows advertisement of service descriptions, enables
dynamic discovery and binding of compatible services.
Used in conjunction with UDDI registry
4. Provides a normalized description of heterogeneous
applications.
Livermore July 25 2001
Client invocation
Single stub can invoke services over different bindings
Depends only on abstract interface.
Are independent of binding (but pluggable).
Add new bindings without recompiling/redeploying stub
Allows optimisations RMI-
based on the bindings of service. IIOP
Will support extended Client Proxy SOAP/
object HTTP
services models if described
In WSDL JMS/
MQ
Livermore July 25 2001
WSFL Overview
WSFL describes Web
Service compositions. [ WS]
1. Usage patterns of Web [ WS]
Services: describes
workflow or business
processes. A
2. Interaction patterns: C
describes overall
partner interactions.
Livermore July 25 2001
WSFL Flow Models
Activities represent
Control links define units of processing.
execution flow as a
directed acyclic graph
Activities are associated
[ WS]
with specific typed
service providers
Flow of data is
modeled through
data links.
Activities can be
mapped to the flow
interface
Livermore July 25 2001
Using Flow Models
“Public flows” provide a representation of the service behavior as
required by its users.
Typically, an abstraction of the actual flow begin executed
Defines a “behavioral contract” for the service.
Internal implementation need not be flow-based.
Flows are reusable: specify components types, but not what specific
services should be used!
“Private flows” are the flows executed in practice.
WSFL serves as a “portable flow implementation language”
Same language is used in WSFL to represent both types of processes.
Livermore July 25 2001
Global Models
Global models describe how the
composed Web Services
interact.
A
RosettaNet automated.
C
Like an ADL.
Interactions are modeled as links
between endpoints of two
service interfaces (WSDL
operations).
An essentially distributed
B
description of the interaction.
Livermore July 25 2001
Discovery: Finding Meta-data
Static binding requires
service “libraries”.
Dynamic binding
requires runtime
discovery of meta-data Directory
Directory UDDI
Inspection ADS,
Inspection DISCO
Livermore July 25 2001
UDDI Overview
UDDI defines the operation of a service registry:
Data structures for registering
Businesses
Technical specifications: tModel is a keyed reference to a
technical specification.
Service and service endpoints: referencing the supported
tModels
SOAP Access API
Rules for the operation of a global registry
“private” UDDI nodes are likely to appear, though.
Livermore July 25 2001
Web Service
Web Service
UDDI Relationships
businessEntity
businessEntity
businessEntity
businessService Rosetta-Net
businessService
BASDA
bindingTemplate Simple.Buy
bindingTemplate
InstanceDetails Schemas,
InstanceDetails
Interchange specification
categoryBag tModels
SIC CODE
keyedReference
keyedReference NAICS
identifierBag
DUNS Numbers
keyedReference
keyedReference Thomas Registry ID
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3. Summary
Livermore July 25 2001
Summary
The Web services framework is being defined,
standardized and supported by the industry at a record
pace.
Broad industry acceptance and standard compliance will
make it ubiquitous.
Will bring an unprecedented level of interoperability to
Web applications.
The benefits of Web services, however, are not limited to
the Web!
Livermore July 25 2001
For more information
SOAP
http://www.w3c.org/TR/soap
WSDL
http://www.w3c.org/TR/wsdl
UDDI
http://www.uddi.org
WSFL
http://www.ibm.com/software/webservices
Me:
mailto:curbera@us.ibm.com
Livermore July 25 2001
