摘要:
A method and apparatus are provided for using sibling-counts in XML indices to optimize single-path queries. Using a b-tree XML index with a SQL query logarithmically reduces the number of disk accesses by passing over index entries where it is determined that a match will not be found. However, because certain index entries are passed over, it is impossible to ascertain if a path expression occurs more than once in the XML index, as certain queries sometimes require. This hurdle can be overcome by maintaining a sibling count with each node entry in the XML index. Because the sibling count is stored with the index entry, the index will reveal whether the matching node is single or has other siblings. In additional to re-writing the original query for optimization by use of an XML index, it will be re-written to check for a single-path condition in the index.
摘要:
A method and system for evolving XML-schema-based data to conform to an evolved XML schema is disclosed. Based on an existing XML schema and an instance document that is based on the existing XML schema, an XML-schema-independent form of the instance document is generated. Based on a set of specified transformations and the XML-schema-independent form of the instance document, an evolved instance document is generated. The evolved instance document conforms to an evolved XML schema that incorporates changes to the existing XML schema. Techniques described herein are flexible enough to accommodate a wide variety of evolutions to XML schemas.
摘要:
A method and system are provided for extracting a valid, self-contained fragment for a node in a XML document stored in a database management system. An XML index is used to identify a location in which XML fragment data corresponding to the node is located. Ancestors of the node are identified and examined for any information needed for the proper interpretation of the fragment. If an ancestor node contains such needed information, this information is patched into the XML fragment to ensure that the fragment is a valid, self-contained XML fragment.
摘要:
Various techniques are described hereafter for improving the efficiency of binary XML encoding and loading operations. In particular, techniques are described for incrementally encoding XML in response to amount-based requests. After encoding enough binary XML to satisfy an amount-based request, the encoder stops encoding the XML until a subsequent request is received. The incremental encoding may take place on the client-side or the server-side. Techniques are also described for reducing the character set conversion operations by having a parser convert tokens in text XML into one character set while converting non-token text in the text XML into another character set. Techniques are also described for generating self-contained binary XML documents, and for improving remap operations by providing a binary XML document on a chunk-by-chunk basis.
摘要:
A method and apparatus for estimating the cost of streaming evaluation of XPaths is provided. Aggregate statistics are maintained by the database server upon initiation of a database function by the database administrator about the nodes of the XML document. Based upon these statistics and the complexity of the particular XPath query, an estimate of the cost of the query, in time and computing resources required, is computed.
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:
Techniques and systems are provided for efficiently managing hierarchical relational data stored in object-relational database system by extending the syntax of the database language supported by the database system (e.g. SQL) to incorporate several new “hierarchical” operators. These operators are evaluated based on the hierarchical relationship defined for hierarchical relational data. The operators maybe incorporated in SQL queries along with relational operators.
摘要:
To improve performance of performing XML operations on an XML document in by a client tier, the client generates an index that indexes the nodes of an XML document. The index may be generated, for example, by and during parsing of the XML document. The index contains similar structures to those maintained by a database server to perform XML operations on collections of XML documents. In lieu of parsing XML document to generate an index, the client may generate indexes based on data retrieved from the indexes at the database server.
摘要:
A method and apparatus for efficiently maintaining XML index structures in a database system is provided. Instead of immediately synchronizing the XML index structures for every change submitted to the database, the changes are stored in a PENDING table. The XML index structures are periodically synchronized, based on certain criteria or at a user's discretion. Between synchronizations, the XML index structures may be in stale mode or current mode. If in stale mode, a request to access indexed information will use the XML index structures to find the desired indexed information without checking the PENDING table. If in current mode, a request to access indexed information will search the XML index structures and also check the PENDING table to determine 1) whether the indexed information has been updated or deleted, and 2) whether information relevant to the request has been inserted or updated.