Hartmut Liefke

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We describe a tool for compressing XML data, with applications in data exchange and archiving, which usually achieves about twice the compression ratio of gzip at roughly the same speed. The compressor, called XMill, incorporates and combines existing compressors in order to apply them to heterogeneous XML data: it uses zlib, the library function for gzip,(More)
Over the last few years, efficient access to heterogenous data sources has become tremendously important. One common technique for increasing efficiency is to maintain locally sorted views in data warehouses, which must be kept current with respect to the changes in the underlying data sources. While this problem has been extensively studied in the context(More)
We have implemented a compressor (XMilI) and decompressor (XDemill) for XML data, to be used in data exchange and archiving, which can be downloaded from http://www.research.att.com/sw/tools/xmill. XMill compresses about twice as good as gzip, at about the same speed. It does not need a DTD in order to compress, and preserves the input XML file faithfully,(More)
We describe a tool for compressing XML data, with applications in data exchange and archiving, which usually achieves about twice the compression ratio of gzip at roughly the same speed. The compressor, called XMill, incorporates and combines existing compressors in order to apply them to heterogeneous XML data: it uses zlib, the library function for gzip,(More)
A query language is essential, if XML is to serve effectively as an exchange medium for large data sets. The design of query languages for XML is in its infancy, and the choice of a standard may be governed more by user acceptance than by any understanding of underlying principles. One would hope that expressive power, performance, and compatibility with(More)
Abst ract Query languages and their optimizations have been a very important issue in the database community. Languages for updating databases, however, have not been studied to the same extent, although they are clearly important since databases must change over time. The structure and expressiveness of updates is largely dependent on the data model. In(More)