1. A computer-implemented method of extracting a datapoint from a markup language document using multiple extraction rules, the method comprising: applying a first extraction rule to a structural graph representation of the markup language document to generate a first correlation value for each of a plurality of nodes of the structural graph representation, each first correlation value representing a degree to which the respective node is correlated with the first extraction rule; applying a second extraction rule to the structural graph representation of the markup language document to generate a second correlation value for each of the plurality of nodes of the structural graph representation, each second correlation value representing a degree to which the respective node is correlated with the second extraction rule, wherein the first and second extraction rules correspond to a common datapoint; and selecting, from the plurality of nodes, a single node from which to extract the datapoint, wherein selecting said single node comprises, by a computer system: (a) comparing the first correlation values to each other to identify a node most closely correlated with the first extraction rule, (b) comparing the second correlation values to each other to identify a node most closely correlated with the second extraction rule, (c) determining whether the node most closely correlated with the first extraction rule is the same as the node most closely correlated with the second extraction rule, and (d) when the node most closely correlated with the first extraction rule is not the same as the node most closely correlated with the second extraction rule, selecting one of said two most closely correlated nodes based on a comparison of their respective correlation values.