The invention is directed at a method and apparatus for determining compression state information which is to be used in the compression of data being transmitted between two communicating parties. The method of determining the compression state information for use in interactively compressing data comprises the steps parsing the data to determine a hierarchical data structure of the data; traversing a shared hierarchical node index to determine common compression state information entries between the hierarchical data structure and the hierarchical node index; and selecting at least one of the common compression state information entries for use in compressing the data.