摘要:
A method and apparatus for accelerating value-based lookups of XML documents in XQuery is provided. XML indices can help to optimize SQL queries of XML documents stored in object-relational databases. Certain SQL/XML functions such as XMLTABLE( ) use XQuery expressions to query XML documents. Previously, such queries could not use the XML index because the PATH table of the XML index was not defined for XQuery semantics. Techniques described herein extend the XML index for use with queries that require evaluation of XQuery expressions. Consequently, techniques described herein accelerate value-based lookups of XML documents in XQuery by introducing the possibility of an index-assisted evaluation of XQuery expressions.
摘要:
Approaches are provided for improving the performance of certain database queries that operate on binary-encoded XML. In particular, the approach uses occurrence and type constraint information about XML data stored in the database for optimizing the relational rewrite of a query. Constraint information can be obtained in several different ways including through a formal language specification such as an XML Schema or DTD, through discovery of a user-provided secondary index on a an XML path table, or through a structural summary that is derived from statistical analysis on a set of XML documents stored in the database.
摘要:
Techniques for processing a query that includes a path expression are provided. A query processor determines whether an XML index may be used to execute the query instead of having to scan multiple XML documents. The query is parsed and normalized, which results in multiple normalized path expressions that are based on the original path expression. If the XML index is a path-subsetted index, then the query processor generates annotated path expressions based on the normalized path expressions. The query processor determines whether each of the annotated path expressions is satisfiable by the path-subsetted XML index. If so, then the XML index is used to process the query.
摘要:
A method and apparatus for accelerating value-based lookups of XML documents in XQuery is provided. XML indices can help to optimize SQL queries of XML documents stored in object-relational databases. Certain SQL/XML functions such as XMLTABLE( ) use XQuery expressions to query XML documents. Previously, such queries could not use the XML index because the PATH table of the XML index was not defined for XQuery semantics. Techniques described herein extend the XML index for use with queries that require evaluation of XQuery expressions. Consequently, techniques described herein accelerate value-based lookups of XML documents in XQuery by introducing the possibility of an index-assisted evaluation of XQuery expressions.
摘要:
Techniques are provided for indexing XML documents using path subsetting. According to one embodiment, a PATH table created for storing one row for each indexed node of the XML documents using user-defined criteria. The user-defined criteria are used to determine which nodes of XML documents to included in The PATH TABLE. The PATH table row for a node includes (1) information for locating the XML document that contains the node, (2) information that identifies the path of the node, and (3) information that identifies the position of the node within the hierarchical structure of the XML document that contains the node. Use of the user defined criteria is transparent to any query improves DML indexes overhead costs.
摘要:
In a database system, names and namespace of XML nodes are computed from path ids. The path ids are constructed from tokens, each of which represents a particular name or namespace-name pair.
摘要:
Techniques are described herein for efficient and scalable processing of complex sets of XML schemas. The techniques described herein provide for reducing duplication of schema elements in volatile memory by building an XML schema in-memory model that stores repeating schema elements in in-memory data structures that are separate from in-memory data structures that store the parent schema elements which logically include or otherwise refer to the repeating schema elements. The techniques described herein also provide for faster generation of an in-memory model of an XML schema by pre-loading, in data structures on persistent storage, of schema elements from dependent XML schemas that are referenced and/or incorporated by the XML schema. The techniques described herein also provide for efficient processing of inter-dependent XML schemas by tracking all unresolved schema elements from dependent XML schemas and freeing the portions of volatile memory, which are used to process schema elements from the dependent XML schemas, as soon as the dependent schema elements being processed are stored in data structures on persistent storage.