2. The transformation rule generation supporting apparatus according to claim 1 , wherein: the graphical representation of the transformation rule includes a set of nodes representing input elements, a set of links each representing a hierarchical relationship between two different nodes in the set of the nodes representing the input elements, the set of nodes representing output elements, a set of links each representing a hierarchical relationship between two different nodes in the set of the nodes representing the output elements, and a set of links representing correspondence between the nodes representing the input elements and the nodes representing the output elements; each node and each link have associated therewith at least one of a pattern for use in matching performed for each element in a structured document to be transformed and an output-related parameter; and the computer readable instructions further comprise: generating a transformation rule in text form for a processing-target node taken from the set of the nodes representing the input elements in the input sort order, the transformation rule instructing, on condition that matching using the pattern associated with the processing-target node succeeds for an element in the structured document to be transformed, to output an output element represented by a node mapped by a link to the processing-target node, on the basis of the output-related parameter associated with the link and the output-related parameter associated with the node representing the output element.
2. The transformation rule generation supporting apparatus according to claim 1 , wherein: the graphical representation of the transformation rule includes a set of nodes representing input elements, a set of links each representing a hierarchical relationship between two different nodes in the set of the nodes representing the input elements, the set of nodes representing output elements, a set of links each representing a hierarchical relationship between two different nodes in the set of the nodes representing the output elements, and a set of links representing correspondence between the nodes representing the input elements and the nodes representing the output elements; each node and each link have associated therewith at least one of a pattern for use in matching performed for each element in a structured document to be transformed and an output-related parameter; and the computer readable instructions further comprise: generating a transformation rule in text form for a processing-target node taken from the set of the nodes representing the input elements in the input sort order, the transformation rule instructing, on condition that matching using the pattern associated with the processing-target node succeeds for an element in the structured document to be transformed, to output an output element represented by a node mapped by a link to the processing-target node, on the basis of the output-related parameter associated with the link and the output-related parameter associated with the node representing the output element. 10. The transformation rule generation supporting apparatus according to claim 2 , wherein the computer readable instructions further comprise generating the graphical representation of the transformation rule for a selected portion in response to a user selection of a portion in the transformation-source structured document; wherein on condition that the selected portion is part or all of a table, the computer readable instructions further comprise generating: a node representing a parent output element for a first row in the selected portion, the node having associated therewith an element name corresponding to the first row, and a node representing an output element for each cell on the right of a leftmost cell in the first row as a child of the parent output element node, the child node having associated therewith an element name corresponding to the cell, sequentially from the left; a node representing a parent input element for the leftmost cell in the first row in the selected portion, the node having associated therewith a position-coordinate matching pattern that is set to position coordinates of the leftmost cell, and a link mapping the node to the node representing the parent output element; a node representing an input element for each cell on the right of the leftmost cell in the first row in the selected portion, the node having associated therewith a scanning-direction matching pattern that is set to right, the node being generated as a child of the parent input element node for each of first two cells, and being generated as a child of an input element node corresponding to an immediately preceding cell for each of remaining cells, sequentially from the left; and a link mapping each node representing the child input element to the node representing the child output element having a corresponding attribute name associated therewith.