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 for managing XML data associated with multiple execution units ensure that execution units are able to use XML data coming from other execution units. Such techniques are applicable when, but for the technique, an XML type value is produced in a particular form by one execution unit and is supposed to be consumed by another execution unit that is unable to process data in the particular form, and involves detecting that the foregoing situation exists and annotating information sent to an XML producer execution unit to cause the XML type value to be transformed into a canonical form that can be shared by all relevant execution units.
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:
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:
Techniques are provided for processing a query, including receiving the query, where the query specifies certain operations to be performed, including (a) a first set of one or more operations that are to be performed on a markup language data source and (b) a second set of one or more operations that are to be performed on a second data source. Then it is determined that a first server that manages the markup language data source is capable of performing the first set of operations. A request is sent to the first server to perform the first set of operations. A response is received, where the response contains results of performing the first set of operations on the markup language data source. Finally, results are generated for the query based at least in part on the results of performing the first set of operations.
摘要:
Object-relational database systems process XML values in a way that preserves node identities of nodes in the XML values and perform node-id based operations more efficiently or even in circumstances where such operations were not performed. An object-relational database system represents an XML value as a serialized stream of bytes, herein referred to as a serialized image. A serialized image may represent an XML value of the XMLType that is stored and/or generated by an object-relational database system. The serialized image contains one or more node identifiers that identify nodes within the XML value. The serialized image may also contain a pointer to an in-memory representation of the XML value, allowing the in-memory representation to be accessed via the pointer without having re-create the in-memory representation.
摘要:
Techniques are provided for processing a query including receiving the query, where the query specifies certain operations; determining that the query includes a first portion in a first query language and a second portion in a second query language; generating a first in-memory representation for the first portion; generating a second in-memory representation for the second portion; generating a third in-memory representation of the query based on the first in-memory representation and the second in-memory representation; and performing the certain operations based on the third in-memory representation.
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.
摘要:
An XQuery access API is described, for providing access to XML data from a data source, using the XQuery language. A requestor can request, from a server, performance of an operation on XML data, wherein request messages and response messages conform to the Simple Object Access Protocol (SOAP). Request and response messages can be transmitted using Hypertext Transfer Protocol (HTTP) or Hypertext Transfer Protocol over Secure Socket Layer (HTTPS). The format of the request and response messages is specified in a definition of a Web service, where the definition conforms to the Web Service Description Language (WSDL).
摘要:
Disclosed is a method and mechanism for processing expressions and operator trees. An approach is particularly useful to optimize processing of XML statements with respect to SQL operators. A top-down processing approach can be taken to directly output data from operators to a data stream. In addition, multiple processing approaches can be taken within a single expression tree, with some operators processed using the top-down approach and other operators processed with the bottom-up approach. Even data that can not be streamed is copied fewer times using this approach, intermediate values from bottom-up processing may still be streamed if it is used by an operator that is eligible for top-down processing.