1. A method of determining a hybrid text summary by a hybrid summarization system having a processor, a relevance score determination module, a structural representation of the discourse determination module and a percolation module, the method comprising: determining discourse constituents for a text by the processor; determining a structural representation of discourse for the text by the structural representation of the discourse determination module; determining relevance scores for discourse constituents based on at least one non-structural measure of relevance by the relevance score determination module; percolating relevance scores based on the structural representation of discourse by the percolation module; and determining a hybrid text summary, by the processor, based on discourse constituents with relevance scores compared to a threshold relevance score, wherein percolating the relevance scores comprises: for each child discourse constituent node in the structural representation, assigning the relevance score of the child discourse constituent node to the parent discourse constituent node if the child discourse constituent node is more relevant; for any subordinating nodes, assigning the relevance scores of the subordinated discourse constituent to the subordinating discourse constituent if the subordinated discourse constituent is more relevant; and for any coordination nodes, assigning the relevance score of the most relevant child to other child discourse constituent nodes.