As discussed in previous sections, the SNAT model of a transformation defines three primitive operations – context-propagator, context-distributor, context-atomizer. Among these, it is the context-propagator which represents navigation: the mapping of a set of source nodes to another set of source nodes. The input of this mapping is the source context of an individual target node; the output of this mapping is the (collected) source context of the child nodes of this target node.