• The KIPS Transactions:PartD
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• v.8D no.6
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• pp.799-812
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• 2001

As XML become more popular for encoding data and exchanging format on the web, recent work on processing XML Document in DBMS has been performed. However, there is no formal data model for XML, and there is lack of research on XML algebra for processing complex XML query and even the mediators have many restrictions. Therefore, this paper proposes formal data model and algebra based on directed edge labeled graph for XML query. To implement algebra, not only algorithms of operation for algebra are presented, but also they are implemented using access method and path index based on RDBMS or ORDBMS. In particular, experiments to show the effectiveness of the implemented algebra are performed on XML documents on EST data which are semistructured data.

• Journal of KIISE:Databases
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• v.28 no.3
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• pp.468-483
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• 2001

In order to enhance the performance, cursor stability, which is a variant of isolation lvel 2 in relational DBMSs, has been widely used in place of isolation level 3, which uses strict two phase locking. However, cursor stability is much less usable in object-relational DBMSs (ORDBMSs) because navigational applications in ORDBMSs can suffer from critical inconsistency problems such as dangling pointers, lost updates, and reading inconsistent complex objects. In this paper, we propose a new isolation level, navigation stability, that prevents the inconsistency problems of cursor stability for navigational applications, while avoiding significant degradation of the concurrency of level 3. First, we analyze the inconsistency problems of cursor stability for navigational applications. Second, we define navigation stability as an extension of cursor stability and show that it solves those inconsistency problems of cursor stability in ORDBMSs. For workloads consisting of transactions of long duration, compared with level 3, the throughput of navigation stability is enhanced by up to 200%; the average response time reduced by as much as 55%; and the abort ratio reduced by as much as 77%. From these results, we conclude that navigation stability is a useful isolation level in ORDBMSs that can be used in place of isolation level 3 to improve the performance and concurrency without significantly sacrificing consistency.