url - Universität zu Lübeck
url - Universität zu Lübeck
url - Universität zu Lübeck
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100 CHAPTER 5. THE KEY-ORIENTED XML INDEX KEYX<br />
The descendant query Q 5 selects all isbn nodes without regarding their leading<br />
path. Because Q 5 has no key it cannot be executed by a Raw Path. The other<br />
approaches provide similar results. Due to the medium size of the result set the<br />
process of finding relevant nodes is more expensive than fetching them from the<br />
database. On the other hand, the navigation inside the structural summaries is<br />
performed so fast that there is no significant difference between APEX and the<br />
Strong DataGuide. As the DBLP data is relatively high structured it contains only<br />
few element types (e.g. inproceedings, title, isbn). Thus, the extent of one element<br />
type can quickly be retrieved.<br />
Figure 5.16: Performance measurements of query Q 5<br />
Partially matching queries are evaluated by the query q 6 that is executed upon the<br />
indexes i q2 for q 2 and index i q3 of q 3 . In both cases the execution time lasts a bit<br />
longer than by using an optimal index. When executing q 6 upon i q2 the relative<br />
navigation step ../title is executed on the elements which are referenced by the<br />
result of i q2 .<br />
Figure 5.17: Performance measurements of query Q 6
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