The problem of managing versions in XML documents can be approached through traditional adapted procedures, based on managing XML operations (deltas) or using timestamped markups to represent the validity of each versioned tag within the document. The first solution entails a high reconstruction cost for any version different from the current one. Whereas the second solution, due to the linear nature of time, implies that these techniques do not to support branched versioning. In this work, the XML data model is extended for the representation of different versions of XML documents that consists of marking the tags with a versionstamp instead of using a timestamp. This technique is based on two ideas: on the one hand storing the ancestral relations of the versions (version tree) produced a new version is generated and on the other hand the version validity of each versioned tag is defined based on this tree (versionstamp). The easy management of multiple versioning, the wide number of queries in XML standard query languages and its implementation only using XML technology, are some of the advantages of the proposed technique.
The goal of this paper is to show our experience in the design of an extension to an XML native database in order to add in a native way version features. Due to the lineal nature of time, XML timestamped solutions for the management of XML versions have difficulty in supporting non-linear versioning, and their implementations are scarce and not very portable. From our technique described in [6,7], which allows us to manage branch versioning, we have developed our versioning system focusing on its high portability and platform independence properties. To achieve this, our versioning system is based exclusively on XML technology. The system is composed by XQuery modules, so that this allows its use not only in an XQuery engine but also in an XQuerysupport XML native database. To test it, the modules have been integrated in an eXist XML native database, an XML difference tool is used to observe the changes made between versions, and the eXist web interface has been extended to make the management of XML versions easier.
This paper describes and evaluates new methods for relation declustering in parallel databases. To process queries in parallel, relations are partitioned across multiple processors, typically by using the value of one single attribute. This kind of declustering has resulted in poor performance in the presence of data skew. Alternatively, the work contained herein proposes several strategies to decluster a relation through the use of multiple attributes.To demonstrate the validity of our approach, a thorough performance evaluation is done. The findings demonstrate the effectiveness of this kind of partitioning methods as opposed to traditional ones. In addition we analyze the performance of the different strategies relative to the speed-up and scale-up metrics.To sum up, performance results reveal that multi-dimensional declustering methods constitute a very promising alternative to conventional one-dimensional methods to partition relations in parallel database systems.
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