tailieunhanh - Tradeos in XML Database Compression

Oracle Label Security adds extensive protection for sensitive information. It delivers multilevel security capabilities to protect access to data right down to individual rows in tables and addresses the real world data security and privacy problems faced by government and commercial entities worldwide. Oracle Label Security can be combined with Virtual Private Database, Secure Application Roles, and Oracle Database Vault to provide powerful solutions for protecting personally identifiable information. . | Tradeoffs in XML Database Compression James Cheney University of Edinburgh Edinburgh EH8 9LE United Kingdom 44 0 131 651 3842 jcheney@ Abstract Large XML data files or XML databases are now a common way to distribute scientific and bibliographic data and storing such data efficiently is an important concern. A number of approaches to XML compression have been proposed in the last five years. The most competitive approaches employ one or more statistical text compressors based on PPM or arithmetic coding in which some of the context is provided by the XML document structure. The purpose of this paper is to investigate the relationship between the extant proposals in more detail. We review the two main statistical modeling approaches proposed so far and evaluate their performance on two representative XML databases. Our main finding is that while a recently-proposed multiple-model approach can provide better overall compression for large databases it uses much more memory and converges more slowly than a single-model approach. 1 Introduction Over the last few years XML has become popular as an exchange format for large data collections including scientific databases like the Georgetown Protein Structure Database and UniProt as well as bibliographic databases such as Medline and DBLP . We refer to such documents as XML databases. Due to the high redundancy of XML s text representation compression is clearly needed for storing and transmitting XML databases efficiently. Although there is no obstacle to using general-purpose text compressors to compress XML and this is what is done most frequently in practice several researchers have proposed XML-specific compression techniques which take advantage of the structure of XML to improve compression beyond what is typically achieved by text compressors alone. The first such effort was Liefke and Suciu s XMill 8 a compressor which splits