This is a subject that I have been working on for quite some time, and the more I have investigated this subject, the moreI have realized that this model is very powerful in today's ever changing business world. This model allows your BPEL processes to be very dynamic, both from a development point of view and from a runtime point of view by adding an additional intangible runtime value. Lets review each of these individually first. Please note that this blog post will not contain any code examples.
Dynamic BPEL PartnerLinks
In a lot of development environments, we sometimes do not know what service we are going to call or for that matter where does this service resides. So its very hard at development time to provide an endpoint to our BPEL process, so the questions to answer are what service do we call, and where does it live?
This is where dynamic partnerlinks come in handy, they resolve both questions, by providing the answers at runtime (magically ;o) ). Well not really magically but these values are passed to the BPEL process at runtime, and using the ws-addressing feature of BPEL PM we can invoke and receive callbacks from these dynamic endpoints, without having to provide these values at design time. The only caveat is that you need to know the data model of your service that you will be calling, so you need to know the XSD or a variant of the XSD. For an example please visit the BPEL Cookbook on OTN. (I have a working example of dynamic partnerlinks for 11G, which I will post at a later date).
Dynamic Routing of BPEL processes
This aspect of the model relates to using some sort of a Business Rules Engine, which will route your workflow based on some business logic/events, all of it dynamic. So the only two things given would be the start and the end, what path was taken to get to the end will not be known at design time, its only at runtime that all will unfold and told. There are no caveats here, but you need to design and develop your business rules, make them available to BPEL to allow for dynamic routing of your workflows.
Now if we take the dynamic partnerlinks and combine it with dynamic routing, you end up with a double whammy, a fully dynamic BPEL process AND workflow!! How many times have you wished for this, well wait no longer, cuz here she is!!
Its a little hard to imagine but the benefits of this model are enormous for e.g.:
- minimum impact on your parent BPEL process, even if you change your endpoints or even the work that the service does, it has no impact on the calling BPEL process
- the only contract between the BPEL process and partnerlinks is the XSD, as long as that stays constant, it does not matter to the BPEL process
- by having all dynamic partnerlinks (or most, or some of them, you may still have to have some static PL), by changing the workflow it does not matter what services are called since they all conform to same XSD contract
- this model allows you to quickly change the partnerlinks and workflow (rules) with no impact on the BPEL process, since these rules and partnerlinks are external to the BPEL process - no redeployment!
-imagine being able to point to another version of your service and only have it called when a certain rule is satisfied, while still having the older service/rule up and running and doing this with NO DOWN TIME!!
Of course with all the benefits come some costs :) and the one cost (not bad odds one cost vs so many benefits) is the contract between services, i.e. the XSD --> for this whole model to work you need to come up with a common XSD for all the dynamic services that will be called, also known as a canonical XSD. Now, this canonical XSD can be a simpler version of a "true" canonical XSD, not as many elements in it, just enough to satisfy the endpoint. But this still means work on your part to come with this legal contract, and it may mean "modifying" services to meet this requirement. Some of the services that you are calling may not owned by you, so it may get tricky unless you can get a confirmation that the XSD's will not change in the near future (and the endpoint/implementation may not change that frequently either).
The thing to note here, this model works best for use cases where you are expecting a lot of change, for example in the legal industry, or policy driven industries (insurance, banks), due to the very dynamic nature of these businesses, they may need to change their process very frequently. If however, your business needs are static and do not except much change, this model may prove to "hectic", though it will not hurt, - if you are looking to implement this approach it would be prudent to do a feasibility exercise first.
Another benefit of this approach, and in my view one of the most important, is for all your long-running BPEL processes - my definition of a long running BPEL process (aka "active durable processes") is a process that cannot survive a rolling upgrade (usually 2 days), i.e. it has to finish where it started.
Processes can run for months/years - the problem with active durable processes is that if you have to change their implementation or if you have to migrate, you need to wait while they finish. Well, with this model, you can make all your active durable processes, into multiple short-running dynamic BPEL processes(a small design change), so any change to their implementation will have no impact at all on the BPEL processes.
So here ya go, a powerhouse at your disposal. As always comments and feedback welcome!