Development of a new indexing technique for XML document retrieval
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The document proposes a new indexing technique for XML document retrieval that addresses issues with existing techniques. It represents an XML document as a tree structure with nodes corresponding to elements, attributes, and content. Nodes are labeled with start/end positions and level to allow efficient updates by leaving gaps between labels. The technique permits fast retrieval of ancestor-descendant and parent-child relationships without recomputing the index on updates. Future work could include indexing comments and handling two separate indices for updates and queries.
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Development of a new indexing technique for XML document retrieval
- 1. Development Of a New Indexing Technique for XML Document Retrieval by: Amjad Ali Amjad
- 2. Agenda Introduction Background Problem Statement Proposed Solution Results and discussions Conclusion and future directions
- 3. Introduction What is XML XML is a markup language much like HTML XML was designed to describe data XML tags are not predefined. You must define your own tags XML uses a Document Type Definition (DTD) or an XML Schema to describe the data
- 4. Introduction (continue) Example Doc 1: <invoice> <buyer> <name>ABC Corp</name> <address>1 Industrial Way</address> </buyer> <seller> <name>Acme Inc</name> <address>2 Acme Rd.</address> </seller> <item count=3>saw</item> <item count=2>drill</item> </invoice>
- 5. Introduction (continue) Database management systems are increasingly being called upon to manage semi-structured data: data with an irregular or changing organization Semi-structured data is often represented as a graph (tree structure) Evaluating queries over semi-structured data involves navigating paths through this relationship structure
- 6. Introduction (continue) Index Construction for efficient access Traditional indexing Techniques are applicable. Parent child nesting relationship Expensive querying for this representation even with indexes
- 7. Introduction (continue) Building specialized data manager For semi-structured data repository Example projects LORE, Tamino, XYZFind Update causes a re-computation How to deal with update problem
- 8. Introduction (continue) Relative Region Co-ordinate Knowledge of start and end position Within the parent element Only need to update the portion of the index file Value indexes on attribute values
- 9. Introduction (continue) Term-based inverted indices on element content when this is a large piece of text. Index on tag name (i.e given a tag name we can return all the elements with the specified tag.
- 10. Background Position based indexing Queries are processed by manipulating the range of offsets of words, elements or attributes. In path-based indexing, the location of words is expressed as structural elements and the paths in tree structures are used for the processing of query.
- 11. Background (continue) Bitcube: A three dimensional indexing for XML Documents According to this technique documents can be hierarchically represented by XML elements. XML documents are represented and indexed.
- 12. Background (continue) Content and Structure in indexing and ranking XML Index structures with a ranking support are therefore needed for fast access to relevant parts of large documents collections. An analysis reveals that ranking parameters related to both the content and structure of data are poorly supported by most known XML indexes.
- 13. Background (continue) Ctree It provides an indexing structure that is based on two levels: path summary and detailed element-level relationships. The first one, the path summary, is a tree that is distracted from the original data
- 14. Background (continue) Indexing for XML Siblings: Given the importance of XPath based query access, Grust proposed R-tree index, we refer to as wholetree indexes (WI). Such index, however, has a very high cost for the following-sibling and precedingsibling axes. In this method they develop a family of index structures, which refer to as splittree indexes (SI), to address this problem, in which (i) XML data is horizontally split by a simple, yet efficient criteria, and (ii) the split value is associated with tree labeling.
- 15. Background (continue) High-performance XML Storage/Retrieval System. The basic idea of this technique is to allocate a field ID to each text data item of the XML element and to register it in the structure index and text index. The structure index manages the hierarchical structure of each field, and the text index manages the field ID and document ID in which query words appears. The structure index is one big data tree and represents the overlapped structure of documents.
- 16. Background (continue) Indexing documents for queries on structure,content and attributes It Explains position-based indexing and path-based indexing to access XML document by content, structure, or attributes.
- 17. Background (continue) Extensible index technique An extensible index technique is proposed to express position information between nodes in a XML document. It is an efficient index technique that simplifies the comparative object applied to a search query and minimizes the reconstruction of index structure by update operation. In addition, they specially proposed extensible index technique with deferred update.
- 18. Problem Statement Support of element addressing Index size becomes very large Doc.ID should include NodeId (Xpath) + Offset Xpath are long Support of typed data Integer, float, simple types of XML schema Requires classical indexes for certain elements
- 19. Problem Statement Query processing (continue) Structural joins Text search Exact search Support of updates Incremental updates would be a plus
- 20. Problem Statement Evaluation criteria Identifiers By element scan Update By join algo. By graph traversal By OID comparison Keyword Search Per node or per document Descendant/Ancestor Search (continue) Incremental Index size By B-tree traversal Entry number Entry size
- 21. Problem Statement (continue) indexing structures use which the absolute address to pinpoint where data resides, update causes a re-computation If the update frequency is high the cost of reconstruction is unbearable Support of updating the indexes is not considered in most of the indexing techniques.
- 22. Problem Statement (continue) Updates are an issue in any such labeling scheme. It is conceivable that a complete re-labeling could be required for each update, the existing techniques do not support the storage of multiple documents in a single time.
- 23. Proposed Technique An XML document instance is a plain-text file that uses markup delimiters (tags) to define the logical structure of a document in a hierarchical fashion. Robert Korfhage proposed three purposes of indexing in IR, which can best take advantage of structured documents. To permit easy location of documents by topic; To define topic areas and hence relate one document to another; To predict relevance of a given document to given information need.
- 24. Proposed Technique (continue) The current structured query and indexing models for XML have not fulfilled these requirements. The ideal system seems to be one that will provide efficient and comprehensive indexing of document content and structure, and be able to support the predicted degree of relevance all matching documents have to a particular query
- 25. Proposed Technique (continue) There is a node corresponding to each element, with child nodes for subelements. However, all attributes of an element node are clubbed together into a single node, which is then stored as a child node of that element node The content of an element node, if any, is pulled out into a separate child node.
- 26. Proposed Technique Ancestor–descendant relationship (continue) a node(S1,E1,L1) is the ancestor of node (S2,E2,L2) Iff S1<S2 ^ E1>E2 Parent–child relationship a node (S1,E1,L1)is the parent of node(S2,E2,L2) iff S1<S2^E1>E2 ^L1= L2-1
- 27. Proposed Technique (continue) S1 and S2 are start labels, E1 and E2 are end labels, and L1 and L2 are level labels in these formulae. We address the update issue by leaving gaps between successive label values.
- 28. Results and discussions System architecture Data Parser (continue) The Data Parser takes an XML document as input, and produces a parse tree as output. Data manager takes each node of tree mark its indices and store it into database.
- 29. Results and discussions (continue) If the node is of mixed type, with multiple content parts interspersed with sub-elements, each content part is pulled out into a separate child node. All processing instructions, comments, and such are simply ignored
- 30. Conclusion and future directions Reconstruction of index file due to a partial update is a problem that XML database applications inevitably have to face We have developed the indexing system that is based on the two indexing techniques extensible index technique and the relative region coordinate based indexing of XML documents with our own proposed scheme which assigns the level numbers to each node of XML documents and document number to each document.
- 31. Conclusion & future directions (continue) Update of the index structure which increases the cost is successfully removed as the index structure remains unaffected after adding the new nodes. Parent child and ancestor-descendent relationship could be found easily for efficient retrieval.
- 32. Conclusion & future directions (continue) all processing instructions, comments, and such which are simply ignored. In a future, it could be created yet another child node of the element node with all such data. An index that is efficient for both update and retrieval may not available.
- 33. Conclusion & future directions (continue) One of alternatives is building two separate indices such that one is suitable when update is frequent, the other is better at query processing. In this case, a transformation mechanism between the indexing structures is needed to be developed.