1. Decentralised Middleware and Workflow Enactment
Daniel Goodman

2. Outline Why do this? Topology of the middleware
Decentralised structuring of middleware
Decentralised execution of workflows
Conclusions

3. Why Another Middleware?
Produced to assist with the analysis of climate prediction .net data.
This data is too large to move, and partitioned in such a way that it is not feasible to write workflows to address a specific partitioning.
Existing workflow languages and middleware fail to address this problem.

4. Topology of Middleware
Middleware is constructed from three elements
Data Store – Constructs data structures from data stored at the resource it resides on.
Data Processor – Performs operations on data structures made up of a single piece, i.e. A Matrix or Set.
Process Coordinator – The component users interact with. This element adjusts the generic workflows to match the partitioning of the data and schedules their execution on the Data Processors.

5. Topology of Middleware

6. Addressing Resources
All Data Structures and Functions are addressed by URI’s.
These URI’s are unique to both the server and the system as a whole
These contain the URL of the server they are currently residing on.

7. Locating servers
Process Coordinators maintain lists of Process Coordinators and Data Processors.
User tells the Process Coordinator the location of a new server.
A call is made using a an argument from an unknown server.
Periodically and when discovering new resources, they synchronise with the other Process Coordinators in their lists.

8. Addition of a Single ServerPC PC PC DP DP

9. Merging Two Sets of ServersPC PC PC PC DP DP

10. Discovery of Services
Data Processors publish XML documents on web servers associated with their address, describing the services they provide. These include:
The name of the function
The namespace (ensures uniqueness)
The arguments and if they are read or write
Data Processors can return different XML documents for different users if they have different access properties
If a function is to be removed, it is removed from the document before, allowing servers time to update their records

11. Decentralised Execution
Workflow execution is decentralised by both:
Multiple Process Coordinators, allowing workflows to be invoked from a range of locations
Once invoked, workflows are broken up and distributed to Data Processors.
Data Processors then communicate with each other
They only refer back to the process coordinator at the end of the execution
Or, if there is a problem they are unable to overcome. i.e. The failure of a Data Processor they are working with

12. Example PC DP DP DP DP

13. Conclusion
Allows many independent institutions to construct and then merge resources
Reduces the need for user interaction to configure middleware
Reduces the number of workflows effected by a failing node
Reduces the amount of network communication.