Composition of RESTful Services

Prof. Cesare Pautasso
http://www.pautasso.info
[email protected]
@pautasso

REpresentational State Transfer

REST defines the architectural style of the Web

Resource Identification through URI
Uniform Interface for all resources:
- GET (query the state, read-only)
- PUT (Create/Update a resource, idempotent)
- DELETE (Delete a resource, idempotent)
- POST (Create/Access a resource)
Multiple representations of the same resource
Hyperlinks model resource relationships and valid state transitions for dynamic protocol description and discovery

REST Architectural Elements

User Agent
Proxy
Gateway
Origin Server
Gateway
HTTP Connector
Cache

REST middleware is primarily designed to scale a single server, which may need to service a large number of clients

A Composite REST service provides an aggregated view over the state of multiple REST services

The behavior of /C is defined by
composing /R and /S

The composite resource /C only aggregates
the state of its components /R and /S

The composite resource /C augments or
caches the state of its components

The composite representation C refers to its component resources /R and /S via hyperlinks

A composite representation is interpreted by the client that follows its hyperlinks and aggregates the state of the referenced component resources

A composite representation may be retrieved from a composite service

Example: DoodleMap

Vote to choose a meeting place based on its geographic location

Composite REST Service

Compose Yahoo! Local Search with Doodle

Composite REST Service

Create a new poll using the locations

Composite Representation

Demo

Composing REST Services

How to program a composite resource?

Business Process Modeling

JOpera (RESTful BPM engine)
BPEL for REST
BPMN for REST

Scripting Languages

S - REST service composition for JS

The S Scripting Language

for Scalable, Stateful, RESTful Services

PPOPP 2012

S: Hello World

service S { 
  res '/hello' on GET { 
  //handle GET request
    respond 'World!'; 
  }
}

Request handlers contain any JavaScript code (with some S extensions)

S: Proxy

service Proxy { 
  res '/hello1' on GET { 
    respond get '/hello2'; 
  }
  res '/hello2' on GET { 
    respond get 'http://api.inf.usi.ch/'; 
  }
}

S: Composition

service Composition { 
  res '/search' on GET { 
    res a = 'http://www.bing.com/?q=$query';
    res b = 'http://www.google.com/?q=$query';
    respond a.get + b.get; 
  }
}

S: Stateful Services

service Stateful { 
 res '/hello' {
  state s = 'World'
  on GET { 
    respond 'Hello ' + s
  }
  on PUT { 
   s = $name
  }
 }
}

S: DoodleMap

service DoodleMap { 
 res '/doodlemap' {
  state id = 0;
  on POST { 
   res yls = 'http://local.yahooapis.com/search' + 
   	     '?query=$query&zip=$zip';
   res doodle = 'http://doodle-test.com/.../polls'
   var local = yls.get;
   var pollurl = doodle.post(xml_format(local,$title));
   state ui_html[id++] = render('GoogleMap', local, pollurl);
   res id {
     on GET { 
       respond ui_html[$id];
     }
   } 
   respond { 302: {"Location": "/doodlemap/"+id}}
   var timer = setInterval(function() { 
     var pollState = res(pollurl).get;
     var participants = countParticipants(pollState);
     if (participants == $maxParticipants) {
       res(pollurl).put("closed");
       clearInterval(timer);
     } 
   },1000);
  }
 }
}

Conclusion

REST service composition extends the role of intermediary to support the aggregation of multiple distributed resources
REST service composition takes advantage of hypermedia to shift some of the composition work (and state) to the client (Composite Representation)
REST composition fits very well with Business Process Management (JOpera, BPEL/BPMN for REST)
S is a RESTful extension to JavaScript to
script stateful and composite services

http://ws-rest.org/2013/

References

Roy Fielding, Architectural Styles and the Design of Network-based Software Architectures, University of California, Irvine, 2000
Leonard Richardson, Sam Ruby, RESTful Web Services, O’Reilly, May 2007, ISBN 0-596-52926-0
Jim Webber, Savas Parastatidis, Ian Robinson, REST in Practice: Hypermedia and Systems Architecture, O'Reilly, 2010
Daniele Bonetta, Achille Peternier, Cesare Pautasso, Walter Binder, S: a Scripting Language for High-Performance RESTful Web Services, 17th ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming (PPoPP 2012), New Orleans, LA, USA, February 2012
Cesare Pautasso, Erik Wilde, Push-Enabling RESTful Business Processes, 9th International Conference on Service Oriented Computing (ICSOC 2011), Paphos, Cyprus, December 2011
Cesare Pautasso, BPMN for REST, In Proceedings of the 3rd International Workshop on BPMN (BPMN 2011), Lucerne, Switzerland, November 2011
Guy Pardon, Cesare Pautasso, Towards Distributed Atomic Transactions over RESTful Services, In: REST: From Research to Practice, Springer 2011
Cesare Pautasso, Composing RESTful Services with JOpera, In: Proc. of the International Conference on Software Composition (SC2009), July 2009, Zurich, Switzerland.
Cesare Pautasso, RESTful Web Service Composition with BPEL for REST, Data & Knowledge Engineering, Volume 68, Issue 9, September 2009, Pages 851-866
Erik Wilde, Cesare Pautasso, (eds.) REST: From Research to Practice, Springer, 2011
Thomas Erl, Benjamin Carlyle, Cesare Pautasso, Raj Balasubramanian, SOA with REST: Principles, Patterns & Constraints for Building Enterprise Solutions with REST, Prentice Hall, 2012

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