I have a system made of 12 windows services, say A, B ... M. They only exchange information via a queue (MSMQ in this case). The system works in linear fashion - an external party calls A, which publishes a message on a queue that B consumes. The format of the output is fixed, say AResult. B reads AResult, does some processing and publishes BResult to service C, etc.
The problem I'm running into now is that services down the pipeline need data not supplied by the previous step. E.g. service F needs properties from BResult.
I've considered a few alternatives, but they all have shortcomings:
Pass a dictionary of all previous results along. That way say F will be able to read AResult, BResult, etc. The problem is this will introduce high coupling, any change anywhere can break other services.
Have a global God object that different services populate. I've done something similar before and it ended very complex.
Maintain a special object of the most useful data and pass it along each result. E.g. D receives CResult and GlobalContextData and publishes DResult and GlobalContextData. The problem is deciding to include in the context and maintaining it.