The work is using BSPA - CCS for BSP - “Bulk synchronous process algebra”. BSPA is bilevel - local level and global level. The programmer can address processors by number within a machine, but can also send messages between machines.
There are two kinds of comm: computation within the par step; and also message-sending for the global transfer step and synchronisation barrier.
The cost model is to expand individual expression to serial form (by expanding par into sum-of-sequence) and from there using “cost rules” to arrive at an expression representing the cost of the calculation. The clever step is the recognition of the semi-ring (?).
how is she locating the barrier expressions? sync trees?
future work: use the cost model to evaluate the need for parallel processing, whether it would help or not in specific circumstances