Propagation-based structured retrieval is a structure-based retrieval paradigm based on the logical structure of documents. Other structural retrieval paradigms include contextualization and content aggregation. Approaches using propagation view the logical structure of a structured document as a tree whose nodes are components of the document and whose edges represent the relationships between the connected nodes. A document component can be either a leaf or an inner node. Leaf nodes are document components that correspond to the last elements of hierarchical relationship chains and that contain raw data (textual information). With propagation, relevance scores are first calculated for leaf components. They are then propagated upward in the document tree structure to evaluate relevance scores for the inner components.