Funtional Web Service Composition

Functional Composition of Web Services
Rohit Kumar Gupta
Matrikel number : 2557833
Department of Computer Science
University of Saarland
Seminar : Advanced Topics in Service Computing
2 June, 2016
1Functional Composition of Web Services

Outline
1. Introduction
• Web Service
• REST
2. Web Service Composition
• Motivation
• Issues in Web Service Composition
3. State of the Art
4. Proposed Solution
• BPEL for REST
• Control flow for Decentralized Restful Services
• Control flows
5. Evaluation
• Centralized vs Decentralized Web Service composition
6. References

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

Web Service
• What is a Web Service?
- software application
- service over web
- interoperable
- URI
• Example
- single login service is utilized by many applications
Client Server
Software 1 Software 2
Network
Request
Response
login
service
Buxfer
Instagram
Quora

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

REpresentational State Transfer (REST)
REST
- architectural pattern supporting
- modularity
- statelessness
- scalability
- everything is a resource
- every resource has a URI
- format : <protocol>://<application-name>/<ResourceType>/<ResourceID>
- Example - http://amazon.com/products
Standard invocation methods
- Get : provides read only access to resource
- Put : create a new resource
- Post : updates existing resource or create a new resource
- Delete : removes resource

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. Taxonomy
• WSDL
• REST
• BPEL
4. State of the Art
• BPEL for REST
• Control flows
6. Evaluation
7. References

Motivation
• What is a Web Service Composition?
- integration of web services
- high level process
- new utility
Me
Family
Hos-
pital
Police
Insu-
rance
• Real world example : Lets suppose Mr. X had an accident....
4 services :
1. Hospital
2. Family
3. Insurance
4. Police
1
2
3
4
5
6
7
8

Motivation
• If the services are not composed user will have to :
- find each web service separately
- process them and get response
- establish interaction with other web service
- co-ordinance among them
• Why ?
- adds value for client
- wider perspective
- reuse of existing services
-publishable as web services
Me
As Client
Composed
Service as
Server
Hospital Family
Police
Insuranc
e

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. Taxonomy
• WSDL
• REST
• BPEL
4. State of the Art
• BPEL for REST
• Control flows
6. Evaluation
7. References

Core issues in composition
• Service access
- invoking different web services
- handling synchronous and asynchronous response
- management of low level details like interface
• Data flow
- data flow between services
- aggregating
- e.g: cost from Bill service is an input for Payment service
• Data modelling
- formatting
- splitting
- merging
• Control flow
- order of invocation
- decision-making

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

State of the Art
• Web Services Business Process Execution Language (OASIS, 2006)
- assumes WSDL as service interface
- do not support REST features
• REST and Web services in WSDL 2.0 (E. Chinthaka , 2007)
- use new WSDL 2.0 bindings
- WSDL 2.0 is not fully developed to describe Restful web service
- Additional workload of writing WSDL 2.0
• Composing RESTful services with Jopera (Pautasso, 2009)
- stateful composition
• I mentioned these three, there are others as well
Next Target : Implement composition that has all REST features
WSDL – Web Service Description Language

Business Process Execution Language (BPEL)
BPEL
- XML based composition language
- uses WSDL for web service interaction
- internal process control flow
- develops reusable business processes
- basic activities : invoke, receive, and reply
definition of
web service
WSDL
WSDL
WSDL
Client receive
invoke
invoke
reply
Web
service 1
Web
service 2
Flow diagram of BPEL web service

State of the Art

State of the Art
• BPEL, REST web services in WSDL 2.0(2007)
- WSDL 2.0 provides bindings for all HTTP request methods
- BPEL developers create WSDL 2.0 description
- BPEL designed with respect to WSDL 1.1
- lack of semantic information about REST operations
Source : Restful Web Service composition with BPEL for REST

State of the Art

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

BPEL for REST (extension of BPEL for compliance with Restful web services,
Pautasso,2009)
• Invoking Restful Web services
- 4 new activities : get, post, put and delete
- computes and stores URI in BPEL variables
- similar to invoke activity
• Handling invocation failures
- error response (HTTP code : 4xx or 5xx)
- defining fault handlers
• Defining request handlers
- marks progress of composition
- onGet, onPost, onDelete, onPut
• Composition
- receive request
- perform invocation
- inside scope
- outside scope
- inside request handler
-further invocation
-state transition logic
- framing response
defining request handlers
invocation activities according
to business logic
basic intuition
Restful
WS
request

Invocation of Restful web service
fault handlers
address of target resource response received from resource
Meta data
invocation
activity

Publishing Restful web service
tag to publish resource
BPEL variables
request
handlers
framing response

BPEL for REST’s Architecture
Front End : Handles HTTP requests from clients by routing BPEL engine to the corresponding
request handler
Back End : Invoke and bind a Restful services down to an HTTP request-response interaction

Example – E-commerce scenario
Client can :
• place an order
• get order information
•delete order
•update order
•pay
gives product information
and price catalog
composed service
state transition

Implementation Code

Outcome
• Issues addressed
dynamic late binding - appending URI dynamically (extract using XPath language)
dynamic typing - uses header attribute to know content-type dynamically
state transition logic – based on response code
uniform interface
• Open issues
 composition is stateful, BPEL process is centralized
 advanced control flow constructs is not discussed
 dealing with delayed response

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

Control flow for Decentralized Restful Services (Bellido, Alarcon,
Pautasso,2013)
Four issues to handle :
1. Hypermedia Aware
2. Open Connection
3. Decentralization
4. Statelessness
The main focus of this paper include:
• leveraging existing communication protocols
• discuss control flow patterns
• stateless composition of Restful service

Hypermedia aware
1. Hypermedia Aware
- component identification at runtime
- control flow discovery
- awareness about resources using ReLL
2. Open Connection
- handle long running business processes
- using callback connectors
3. Decentralization
- distribution of composition responsibility
- concurrency
- availability of composed service
- load balancing
4. Statelessness
- state information stored at client side
- scalability
- deallocate resources

Hyper media awareness using Resource Linking Language (ReLL)
• Resource Linking Language
- XML document
- resource descriptor
- semantically defines links
- dynamic extraction of data
- contains resource identifier, representation, links to other resources
- composed service invokes descriptor of a resource as needed
Source : Control Flow for Decentralized REST

Open Connection and Decentralization
1. Hypermedia aware
2. Open Connection
3. Decentralization
- concurrency
- load balancing
4. Statelessness
- scalability

Centralized composition
Lets, first consider the case of Centralized composition
Example : we have 3 services
1. Commerce
2. Seller
3. Bank

Open Connection and Decentralized composition
• Each time different resource handles composition state
• Issue of coupling is also handled
Composition logic
and state stored
Component
resources

Statelessness
1. Hypermedia aware
2. Open Connection
3. Decentralization
- concurrency
- load balancing
4. Statelessness
- scalability

Statelessness
Statelessness
- send aggregated state information to composite resources
- composite resource to stores only business logic
- composite resource redirects new state to client with fresh instructions
- callback address of next composite resource to invoke
- composite resource deallocates resources like memory used
- shared responsibility
Client
Composed
resource
• current state + old states received
• request for next instruction
• new state
• next instruction to execute
• callback address
Only business
logic stored
Composition
state stored

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flows
5. Evaluation
6. References

Control flows
Sequence
WS 1 WS 2
Client
Unordered
Sequence
WS 1 WS 2
Client WS 2 WS 1

Control flows … continue
Alternate
WS 1
Client WS 2
Iterative
WS 1
Client
Evaluation condition

Parallel
WS 1
Client
WS 3
Parallel
1. Synchronization – for all
2. Discriminator – for one
3. Partial Join – fixed number
4. Selection – number not fixed
Control flows … continue
Evaluation condition
WS 2

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flow
5. Evaluation
6. References

Centralized v/s Decentralized Web Service composition
Response Time
- total time between sending of request and receiving response
- resource loading and unloading tasks
Parameter
processing capacity : 100 request/sec
queue size : 100 request
n : number of components

Centralized v/s Decentralized Web Service composition ... continue
Availability
- proportion of successful service invocation
- concurrency
Parameter

Centralized v/s Decentralized Web Service composition ... continue
Throughput
- Amount of workload processed per unit time
Parameter

Resolved and Open issues
Open
- handling HTTP response with 200, while removing coupling issue
- dependency on user
- security of data financial data
- unresponsive web services
- handling exchange of massive state information over HTTP
Resolved
- scalability
- statelessness
- decentralization
- control flow
- asynchronous responses

Outline
1. Introduction
• Web Service
• REST
• Motivation
3. State of the Art
• BPEL for REST
• Control flow
5. Evaluation
6. References

References
- A. Lagares Lemos, F. Daniel, B. Benatallah: “Web Service Composition: A Survey of Techniques and
Tools”. ACM Computing Surveys, 48(3), ACM. 2015
- M. Garriga, C. Mateos, A. Flores, A. Cechich, A. Zunino: “RESTful Service Composition at a Glance: A
Survey". Journal of Network and Computer Applications. Elsevier. 2015
- OASIS, Web Services Business Process Execution Language (WSBPEL) 2.0, 2006
- Bellido, J., Alarcon, R., and Sepulveda, C. 2011. Web linking-based protocols for guiding RESTful M2M
interaction.
- Composing restful services with jopera
Cited by :
- Autonomous Composition and Execution of REST APIs for Smart Sensors
- REST Web Service Description for Graph-Based Service Discovery
- An Overview and Classification of Service Description Approaches in Automated Service Composition
Research

Thank You

Funtional Web Service Composition

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