XML components ranking : Which relevant ranking criteria ? Which relevant criteria merging ?

Retrieving specific information becomes an important issue, especially in XML information retrieval (XML-IR). Indexing XML components (elements) rather than the entire XML document allows to target more effectively the relevant elements. In this paper, we consider the problem of ranking the relevant components returned in response to a user query. As opposed to ranking documents, ranking XML elements introduces new criteria to take into account in determining the degree of relevance of a component, as for example the granularity of an XML component or the proximity of query keywords within the XML structure. Our aim is to answer two questions : Which criteria reflect best the relevance of an XML component? and how can these criteria be combined to obtain an efficient scoring function in order to calculate the degree of relevance of an XML component?