Library Web Services for Discovery and Delivery of Scientific Information

Library Web Services for Discovery and Delivery of Scientific Information Access 2006 October 13, 2006 Richard Akerman and Bryan Gahagan NRC CISTI

Overview

Service-Oriented Architecture (SOA)

Web Services

Workflow (BPEL)

Conclusions and Next Steps

SOA and Web Services

Service-Oriented Architecture is a methodology

Web Services are a technology

Service-Oriented Architecture

SOA is a software engineering approach that aims to enable reuse of services, for more flexible and enduring software systems

CISTI uses SOA right now within our Enterprise Architecture

SOA Defined

“In Service-Oriented Architecture autonomous , loosely-coupled and coarse-grained services with well-defined interfaces provide business functionality and can be discovered and accessed through a supportive infrastructure. This allows internal and external system integration as well as the flexible reuse of application logic through the composition of services…to support an end-to-end business process.”

Malte Poppensieker , SOA Weblog , addition from ZDnet SOA blog

Web Services

This is a terrible name.

They are not about the web

They are not (necessarily) about services

“Well-defined networkable functions?”

Another way to slice them is “Vendor-Neutral Middleware”

They have attributes that make them well-suited to SOA

Service Composition – Web Services Workflow

Once you have built several Web Services, you may want to combine them together in various ways, or to use them with other Web Services

This has some flavour of “workflow”

There are lots of existing examples:

Lego

Kama Sutra

Orchestration

Controlling the execution flow of multiple services to expose more complex, composite services

Orchestration server is like the conductor of an orchestra

Oversee and control the flow of execution

Web Service Choreography Interface (WSCI) is W3 standard ( http://www.w3.org/TR/wsci/ )

Business Process Execution Language (BPEL) is OASIS standard ( http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsbpel )

A superset of WSCI functionality

Large vendor support

Before Orchestration

Client Talks Directly to Services

Changes in services interface/workflow affect the client

After Orchestration

Client talks to Orchestration server

Changes to services are applied to Orchestration, Client never knows of the changes

Orchestration can expose an existing service interface or create a new one

Orchestration can use external services

Services used for orchestration can easily be made available externally

BPEL

Express long or complex processes in a standardized XML format

Designed to work with WSDL and web services standards

Services usually invoked with SOAP

BPEL Orchestrations exposed using WSDL

Hierarchal and graph-like control flow.

Execute operations in sequence or,

Follow different links between operations depending on conditions

Message correlation using message data

Long running asynchronous processes

Compensation / error handling within scopes

Abstract Processes

BPEL 1.1

<process name="BPELProcess">

<partnerLinks>...</partnerLinks>

<variables>...</variables>

<faultHandlers>...</faultHandlers>

<sequence>

<receive ... />

<assign ... />

<flow>

<invoke ... />

<invoke ... />

<invoke ... />

</flow>

<reply ... />

</sequence>

</process>

Describe the services or “partners” the process will interact with Stores service request / response messages and other process data Handle any errors that occur when invoking a service Receive message from client, start the process Modify variables to create service request messages or manipulate data Invoke a Web Service, store the response in a variable for later manipulation Replay to client (with a response message) Perform activities asynchronously Perform activities in sequence

BPEL Development and Operations