XN-Store: A Storage Scheme for Native XML Databases

With the growing popularity and application of XML related standards, large repositories of XML documents have emerged on the Web. It is necessary to store these documents into a database to make them manageable. Storage schemes have become an important research topic in the XML data management field. Mapping XML documents to relational tables and storing them into a traditional RDBMS will break down the tree structure of XML data and cause a decline in query efficiency. This paper presents a novel storage scheme, called XN-Store, for native XML databases. Based on the index structure, this scheme directly stores XML nodes as records into a paged file to build up the persistent document object model, thus retaining the original tree structure of XML data. XN-Store not only reduces the storage space overhead of XML documents, but also implements the fast serialization and access of XML nodes. As a general purpose native XML storage scheme, XN-Store supports the creation of various secondary indexes to improve the efficiency of XML query processing. Extensive experiments are conducted on XN-Store and several previous XML storage schemes using a range of real and synthetic datasets, comparing the storage space, storage time, serialization time and node access time. The experimental results show that XN-Store is a high performance storage scheme for native XML databases.