26. The method of claim 24 wherein the first part of the tree-based structure satisfies a tree-based criterion, and the partial tree-based structure satisfies the tree-based criterion.
24. A method for forming a plurality of rules for computer-assisted translation from a source language to a target language, the method comprising: accepting a training corpus comprising a plurality of paired token sequences, one sequence of the pair being a sequence of source language tokens and another sequence of the pair being a sequence of target language tokens; for each of the plurality of paired token sequences, identifying a tree-based structure corresponding to the sequence of source language tokens of the paired token sequence, the tree-based structure representing one or more asymmetrical relations within a plurality of target tokens associated with the tree-based structure and provides an association of the plurality of target tokens with the sequence of source language tokens of the rule for at least some of the paired token sequences, identifying one or more partial tree-based structures, the partial tree-based structure being formed by substituting a first part of the tree-based structure with an element representing an unspecified sequence of source language tokens, the first part of the tree-based structure corresponding to a first part of the sequence of source language tokens of the paired token sequence; and forming, using a computer, the plurality of rules such that each rule is associated with either one of the identified tree-based structures corresponding to a sequence of source language tokens of a paired token sequence or one of the partial tree-based structures.