Tree labeling plays a key role in XML query processing. In this paper, we propose a new labeling scheme, called Clusteringbased Labeling. Unlike all previous labeling methods, In this labeling scheme elements are separated into various groups, and a label is assigned to a group of elements instead of one element. Based on Clustering-based Labeling we design a new relational schema, similar to OrdPath scheme, for storing XML documents in relational database. Grouping Sibling nodes into one record reduces number of relational records needed for XML document storage.