This paper establishes the rate region for a class of source coding function computation setups where sources of information are available at the nodes of a tree and where a function of these sources must be computed at the root. The rate region holds for any function as long as the sources' joint distribution satisfies a certain Markov criterion. This criterion is met, in particular, when the sources are independent. This result recovers the rate regions of several function computation setups. These include the point-to-point communication setting with arbitrary sources, the noiseless multiple access network with "conditionally independent sources," and the cascade network with Markovian sources.

36 pages, Submitted to IEEE Transactions on Information Theory