Generating Relations from XML Documents

Question

1. What have the authors contributed in "Generating relations from xml documents" ?

2. What is the GYO-reduction of a hypergraph?

3. What is the main problem of relation generators?

4. What is the semantics of the relation generator?

Accepted Answer

This paper discusses several mechanisms for creating relations out of XML documents.

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The GYO-reduction of a hypergraph is the result of applying ear removals (combined with the removal of nodes that do not belong to any hyperedge) until there remains no ear in the hypergraph.

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One important open problem is how to define indices over an XML document that will allow relation generators to be quickly evaluated.

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Using the tuple of path expressions Ω = (∗//title, ∗//aname/fname, ∗//aname/fname) the authors can create a relation generator that finds titles with pairs of first names of authors that wrote them.

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Once the interconnection graph was defined in this context, their mechanisms for creating tuples of meaningfully related nodes could be used.

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Since it is possible to find all matchings that do not assign ω1 a null value in polynomial time, the authors can repeat this process for each of the path expressions ωi and thus, derive a polynomial algorithm for computing MMat rT (Ω,m).

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The pseudo natural join of relations with an acyclic hypergraph can be computed in polynomial time, in a fashion similar to computing the natural join.

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Then MMat cT ((ω1, . . . , ωm), k) can be computed in polynomial time under input-output complexity if the following conditions hold:1. either k = 0 or T is non-recursive, 2. H(Rω1,T , . . . , Rωk,T ) is acyclic, and 3. for all i, j ≤ k, either– MatchingLabels(ωi, T ) and MatchingLabels(ωj , T ) are disjoint, or – MatchingNodes(ωi, T ) = MatchingNodes(ωj , T ).

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The authors first show that given a relationgenerator Ω, an integer k and a tree T , determining whether MMat rT (Ω, k) is non-empty is an NP-complete problem.

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The authors intend to implement the mechanisms described here and to perform extensive experimentation in order to discover which semantics perform best and return the best results in practice.

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Even when the authors do not allow some of the path expressions to be mapped to the null value, it may still be possible to evaluate a relation generator in polynomial time under input-output complexity.

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As an example, the following query searches for books with a title containing the word XML and either the author Smith or no specified author.+ */ title : XML */ aname : SmithThis query could be evaluated under any one of the three semantics (completeinterconnection, reachable-interconnection or star-interconnection).

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Another scenario where their mechanisms are useful is to create a universal relation interface to a set of documents, thereby enabling a simple and powerful search of the documents.

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Since the sets MatchingLabels(ωi, T ) and MatchingLabels(ωj , T ) are disjoint for all i and j, this tuple contains exactly m different nodes.

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For = s, i.e., when star-interconnected nodes are desired, it is not difficult to see that a relation generator can always be computed in polynomial time.

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The complexity of evaluation is likely to be one of the factors that influence the decision of whichsemantics to employ for a specific purpose.

Generating Relations from XML Documents

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Most frequently asked questions

1. What have the authors contributed in "Generating relations from xml documents" ?

2. What is the GYO-reduction of a hypergraph?

3. What is the main problem of relation generators?

4. What is the semantics of the relation generator?

5. What mechanism could be used to create tuples of meaningfully related nodes?

6. How can the authors find all matchings that do not assign 1 a null value?

7. how can a natural join be computed?

8. What is the NP-complete problem for MMat cT?

9. What is the proof of MMat rT?

10. How do the authors implement the mechanisms described here?

11. What is the way to evaluate a relation generator?

12. What semantics can be used to evaluate a search query?

13. What is the common use of mechanisms for creating relations out of documents?

14. What is the tuple tn in the tree?

15. How can the authors compute MMat sT in polynomial time?

16. What is the important factor in determining which semantics to use?

Figures

Citations

XSEarch: a semantic search engine for XML

Efficient Engines for Keyword Proximity Search.

Efficiently enumerating results of keyword search

Top-k-size keyword search on tree structured data

On the effectiveness of flexible querying heuristics for XML data

References

Multiple Query Processing in Deductive Databases using Query Graphs

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