Abstract: Techniques and systems are disclosed for directly storing semistructured data in a database. According to one aspect, a client application reads data that comprises instances of a parent type. The client application invokes routines associated with the parent type. An array is created for storing instances of the parent type. These routines invoke routines associated with a child type of the parent type. An array is created for storing instances of the child type. The arrays are populated with values specified in the data. According to one aspect, some columns of the arrays may be populated with other values to be stored in hidden columns of database tables. The client application converts the arrays into a data stream that conforms to the format of the database's data blocks. The client application then streams the data to a database server, which writes the data blocks directly into one or more data blocks in the database.

Abstract: A method and apparatus for computing queries in a way that is consistent with an index and the underlying base table is provided. A query is computed such that it is consistent with the state of an index and base table as of the last point at which the index and table were synchronized. For example, if an index is maintained asynchronously then it is not necessarily consistent with its base table when a query is to be run against the table and the index. Therefore, the query is computed such that it will be consistent with the last point at which the index and the table were synchronized. In one embodiment, a System Change Number (SCN) of the last successful synchronization operation is used to perform a flashback query on the table.

Abstract: A method and apparatus for sharing state information among a plurality of servers is provided. A first server receives a request to perform a file operation, such as a NFS file system operation. Thereafter, the first server updates state information to reflect a change in state associated with processing the request. The first server then causes state update information, which identifies the change in state that was made at the first server, to be propagated to a second server. The second server updates state information, stored at the second server, to reflect the change in state associated with processing the request at the first server. Advantageously, a client may send a series of stateful file operations to either the first server or the second server, even if processing any one of the stateful file operation requests requires knowledge of the state of processing prior requests in the series of requests.

Abstract: Techniques are provided for utilizing partition pruning for XML indexes. The computer-implemented method comprises storing XML documents in a document table, which is equi-partitioned with a corresponding index table, and wherein the partitioned document table and the partitioned index table can be searched using a query comprising a partitioning pruning directive.

Abstract: 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.

Abstract: Techniques manage the presence of repeated constructs within a complex type at the time of schema registration. At registration, techniques detect repeated elements in the XML schema and analyze whether the repeated elements are from the same complex type. If so, techniques perform additional analysis to determine a minimal common ancestor. Within the context of a minimal common ancestor, techniques determine the maximum number of times an element may occur in the schema. In a choice content model, the largest maximum occurrence value is selected. In other content models, the maximum occurrence value is determined by adding together the occurrence values for the repeated elements. Then, when an object relational table is generated for the XML schema, the maximum number of times that an element appears in the schema is this value. Techniques retain the advantages of object relational storage, even after a schema evolution.

Abstract: Techniques and systems are disclosed for storing instances of an opaque type in a database according to a direct path loading approach. According to one aspect, an opaque type implementor registers, with a loader application, routines that the opaque type implementor implements. In response, the loader application associates the opaque type with the routines. The loader application reads data that comprises instances of the opaque type. The loader application determines which routines are associated with the opaque type. The loader application invokes the routines, which create an array for storing instances of the opaque type and populate the array with values specified in the data. The loader application converts the array into a data stream that conforms to the format of the database's data blocks. The loader application then streams the data to a database server, which writes the data directly into data blocks in the database.

Abstract: Techniques are provided for incrementally maintaining an XML index built to access XML data that is encoded in binary XML form. Rather than delete and reinsert index entries of all the nodes of a modified XML document, only the index entries of the affected nodes are modified. Consequently, the order key values stored in the index may become inconsistent with the current hierarchical locations of the nodes to which the order key values correspond. Techniques are described for resolving the inconsistencies, and for addressing additional problems that result when the XML index is path-subsetted.

Abstract: Techniques are provided for estimating the cardinality of a virtual result table that is produced by executing path-based table functions within a query, such as the XMLTABLE function. Some path-based table functions apply a path expression to input from a base table of XML documents to select rows to produce the result table. Path statistics are collected for the path expressions for the base table. The path statistics are used to estimate the cardinalities of the result table. The estimated cardinality of the result table is useful for estimating costs of query execution plans that are generated for the query.

Abstract: Efficient evaluation of resource version history queries is enabled by using a data container storing records corresponding to links between successive versions of a resource. The records include: (a) a record identifier, (b) a predecessor identifier, (c) a successor identifier, (d) a predecessor rowset, which comprises the record identifier of each record in which the predecessor identifier in this record is the successor identifier, and (e) a successor rowset, which comprises the record identifier of each record in which the successor identifier in this record is the predecessor identifier. Depending on the nature of a request, a record is identified in which a particular version is identified by either the predecessor identifier or the successor identifier. Either the predecessor or successor rowsets are recursively read, while the predecessor or successor identifiers corresponding to each record read are added to a result set, thereby forming the ancestor or descendant version history.

Abstract: A method and apparatus for reverting a resource to a prior state in time is provided. Changes are committed to a resource at a particular point in time. After the particular point in time, a request, which may be a file system operation request, to revert the resource to a state prior to the particular point in time is received at a database server. In response to the request, the resource is reverted to the state prior to the particular point in time. The current state of the resource ceases to reflect the plurality of changes. Advantageously, if a requestor creates an incorrect version of a resource, the changes made to a schema-based resource are not compatible with the schema, or the changes of multiple requesters are not compatible with each other, the resource may be reverted to the earlier point in time.

Abstract: Populating an XML index is parallelized, providing both inter-document and intra-document parallelism, by using multiple pull-type parser processes to parse respective XML documents in parallel and to call respective ‘instances’ of the function that generates the index entries based on parsed XML node information. The function is configured to operate according to a cursor-type interface model, whereby each function instance can operate on one node at a time in a controlled pull manner rather than in an uncontrolled streaming manner. Hence, the index load procedure flow can be in the control of an application or routine, via the pull parsers, rather than in the control of a serial stream-based parser.

Abstract: During query optimization, XML index and view merge transformations may be interleaved.

Abstract: One embodiment of the present invention provides a system that implements a security policy in a database. During operation, the system receives a request associated with a set of objects in the database. Next, the system obtains a set of access control lists (ACLs) associated with the database, wherein a respective ACL specifies one or more access privileges associated with a user or user group, and wherein a respective ACLs is not specific to a particular object in the database. The system then evaluates the ACLs to obtain a set of ACL results associated with the request and processes the request by applying the set of ACL results to the objects without evaluating the ACLs repeatedly for each of the objects.

Abstract: A mechanism is provided for improving the performance of particular database queries operating on a view comprising binary-encoded XML. The key to improving performance is to determine whether a XML index is available to improve the computation of XPath data before deriving an optimized execution plan for a particular query. When a XML index is not available to help expedite the computation of binary-encoded XML, then deferring the computation of the XPath data until after the view merge stage avoids unnecessary computation of XPaths that are part of the view but not needed for the particular query.

Abstract: 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.

Abstract: 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.

Abstract: A method, mechanism, and computer program product for storing, accessing, and managing XML data is disclosed. The approach supports efficient evaluation of XPath queries and also improves the performance of data/fragment extraction. The approach can be applied to schema-less documents. The approach is applicable to all database systems and other servers which support storing and managing XML content. In addition, the approach can be applied to store, manage, and retrieve other types of unstructured or semi-structured data in a database system.

Abstract: Techniques for estimating the cost of processing a database statement that includes one or more path expressions are provided. One aspect of cost is I/O cost, or the cost of reading data from persistent storage into memory according to a particular streaming operator. Binary-encoded XML data is stored in association with a synopsis that summarizes the binary-encoded XML data. The synopsis includes skip length information for one or more elements and indicates, for each such element, how large (e.g., in bytes) the element is in storage. The skip length information of a particular element thus indicates how much data may be skipped during I/O if the particular element does not match the path expression that is input to the streaming operator. The skip length information of one or more elements is used to estimate the cost of processing the database statement.

Abstract: One embodiment of the present invention provides a system that facilitates performing a cost-based optimization of authorization checks in a database system. During operation, the system receives a query at the database system. Next, the system estimates a cost for executing the query, which involves estimating a cost for evaluating authorization checks, which involve functional evaluations of access rights for data accessed by the query. The system then rewrites the query to include evaluating authorization checks within the query. The system also estimates a cost for executing the rewritten query. Next, the system determines if executing the rewritten query has a lower cost than executing the query and performing the authorization checks. If so, the system executes the rewritten query. However, if not, the system executes the query.