** on adopting content-based routing in service oriented architectures

WS-Eventing and WS-Notification are defined in SOA to introduce asynch notifications among web services.

WS-Notification has the following parts

• WS-Base Notification
• WS-Brokered Notification
• WS-Topic
  

WS-Notification gets close to WS-Eventing when it comes to WS-Base Notification which introduces the core roles of

• notification producer
  
• subscription manager: enables a subscriber to pause/resume/cancel a subscription
  
• subscriber
• notification consumer

WS-Brokered Notification introduces concept of notification broker rather than direct communication between the source and the sink of messages.

ESB also supports Content-Based Routing (CBR) in order to transfer messages from one service to another in a B2B type of interaction. Messages can be routed based on some pre-defined rules.

Mule and IBM Web Sphere are examples of ESB messagebrokers.

** Addressing QoS for pub/sub and CBR systems is a challenge

Different discovery approaches

• SeCSE: an apprach based on facets for discovery of services in different phases
• DIRE is the publication infrastructe developed for SeCSE
• in DIRE registries can hold any type of service
• REDS is used as a pub/sub mechanism to replicate service descriptions
• Service descriptions are shared among all registries subscribed to a topic
  
• WS-Discovery proposal
• IP multicast -> only applicable to large scale systems
• Meteor-S uses MWSDI and JXTA to provide p2p network of UDDI registries
  

overall two methods for service discovery

• replication of service descriptions
• propagation of queries within the network of registries

Vision of SOA promotes an environment which is GLOBAL and OPEN for service providers to offer their services and consumers to access and use them. Composition at runtime is also promoted to enable dynamic adaptation to changes in the environment.

--> PAPER ARGUMENT: a scalable service discovery infrastructure to allow different organizations to offer and access services globally, complemented by a pub/sub infrastructure to suit the needs of those systems that have an inherently asynch behavior and to monitor the environment.

------------

REDS is a framework of java classes to easily build a modular CBR infrastructure.

• Defining message and filter
  
• Routing Strategy can be modified
  

There are three challenges in CBR:

• the matching challenge
• the security challenge
• the reconfigurability challenge

Open issues:

• QoS for the middleware (e.g., how messages are delivered FIFO, random , etc.)
• Dependability vs Scalability
• Expresiveness vs Scalability
• Reflectiveness
• Context-awareness: context information to be used as notifications