摘要:
A universal format is used to create a type representation of XMLType instances that are generated in various ways from various sources. An XMLType Type Tree is represented as a hierarchy of nodes, including leaf item node, composite item node, operator node, aggregate node, referred to herein as an XMLType Type Tree. An XMLType Type Tree serves as a digest of the type structure of XMLType, no matter the source of the XMLType instance or its manner of its generation and it creates one uniform abstraction of the type structure of XMLType for the data-typing analysis of XPath and XQuery during query compile time.
摘要:
A method for processing queries is provided. A first representation of a query is generated, where the query includes a certain operator that is to be performed based on an XPath expression that is expandable into multiple location paths. The first representation of the query is rewritten into a second representation that corresponds to an equivalent query, where rewriting the first representation includes expanding the XPath expression into the plurality of location paths and, based on the certain operator, including a plurality of operators in the second representation, where the plurality of operators include: a first set of operators that is to be performed based on each of the plurality of location paths, and a second set of operators that is to be performed based on data returned from at least one operator included in the first set of operators. The query may thereafter be executed based on the second representation. The second representation may be further rewritten to third representation depending on the physical storage of XML.
摘要:
A method for optimizing queries is described. A query, which includes a first expression for determining whether each of a set of values evaluates to NULL or NOT NULL, is received. At compile-time, a first representation of the query is generated, where the first representation indicates that the query is to be performed based on the first expression. Based on the first expression, a second expression is determined. The second expression is such that the first expression would evaluate to any NOT NULL value if and only if the second expression would evaluate to any NOT NULL value. The second expression, when evaluated, is much more computationally efficient compared with the evaluation of the first expression. Based on the first representation, a second representation of the query is generated, where the second representation indicates that the query is to be performed based on the second expression. Thereafter, the query is executed based on the second representation.
摘要:
A method for optimizing queries is described. A query, which includes a first expression for determining whether each of a set of values evaluates to NULL or NOT NULL, is received. At compile-time, a first representation of the query is generated, where the first representation indicates that the query is to be performed based on the first expression. Based on the first expression, a second expression is determined. The second expression is such that the first expression would evaluate to any NOT NULL value if and only if the second expression would evaluate to any NOT NULL value. The second expression, when evaluated, is much more computationally efficient compared with the evaluation of the first expression. Based on the first representation, a second representation of the query is generated, where the second representation indicates that the query is to be performed based on the second expression. Thereafter, the query is executed based on the second representation.
摘要:
A method and apparatus for rewriting a database command containing an embedded XML expression such that the rewritten database command recites a text function, in lieu of the embedded XML expression, is provided. Advantageously, a DBMS may take advantage of the efficiencies in storing XML data within the database, while avoiding the generation of unnecessary XML elements in processing the query when the XML elements contribute nothing to the outcome of the query. Cost-base or rule-based analysis may be performed to determine how to rewrite a received database command. The database server may functionally evaluate the text function or may use an index defined on a column of the database. The text function may function as a primary filter or may reference a column upon which an index is defined, wherein the index operates at the same or higher level than a column being referenced in the embedded XML expression.
摘要:
To associate XML data objects (“child objects”), stored in rows of relational or object-relational tables, with the appropriate XML data objects (“parent objects”) from which the child objects descend, tables that contain child objects (“out-of-line” tables) are constructed with an additional column. In one embodiment, this column stores values that identify the root objects, in the appropriate table, from which the respective child objects descend. Hence, the root object from which any given object descends is traceable by following the respective value back to the corresponding root object. In one embodiment, this column stores values that identify the complete XML hierarchical path, through multiple tables, back to the root object from which the respective child objects descend. Consequently, XML query language queries against XML documents stored in such tables can be rewritten as SQL queries against the data in the tables, even in the presence of cyclic constructs.
摘要:
Techniques are described for executing queries that have XPath sections that specify unmappable paths. The techniques involve splitting the unmappable paths into (1) a mappable path fragment, and (2) an unmappable path fragment. After an unmappable path has been split into a mappable path fragment and an unmappable path fragment, the XPath section is replaced with a replacement XPath section. The replacement XPath section specifies two operations: a “mappable operation” that is based on the mappable path fragment, and an “unmappable operation” that is based on the unmappable path fragment. The portion of the replacement XPath section that specifies the mappable operation is rewritten to access underlying relational structures. Consequently, when the rewritten query is executed, a smaller amount of XML data needs to be materialized to evaluate the unmappable path fragment than would otherwise have been required to evaluate the original unmappable path.
摘要:
XML table indexes provide a more efficient mechanism for searching data stored in aggregate form. XML table indexes are a set of tables created to project out in column form commonly sought metadata from stored XML documents. By projecting the data includes into column form, queries on the XML documents can be efficiently processed as they can leverage the enhanced functionality provided by the database tables. The XML table indexes may use aliases, partitioning, constraints and other functions to further improve query flexibility and performance.
摘要:
A database server that manages a database retrieves metadata that is stored, within the database, in association with a procedure that is stored in the database. Based on the metadata, a Web service definition is automatically constructed to describe the procedure as a Web service. The WSDL definition can be referenced to construct SOAP messages with the appropriate arguments and in the appropriate format which, when received, are converted to a suitable format for invoking execution of the procedure by the database server.
摘要:
Optimization is provided for database statements involving XML data, e.g., XPath and XQuery, which operate over views that use aggregate set operators, e.g., UNION ALL. As part of a “view merge” stage of query transformation, the query that operates over the view is merged with a query that defines the view. One or more expressions (e.g., operators, predicates, virtual table constructs) from the query that operates over the view are then “pushed down” to operate on the individual underlying XML data constructs. “Branch elimination” is performed based on the structure of the view and the query acting over the view, based on which it is possible to determine whether any of the sub-queries, if executed, would result in the return of zero rows. If so, then such branches are eliminated from the transformed query, leaving a reduced set of data containers on which to execute the query.