Abstract: 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.

Abstract: 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.

Abstract: Instances of complex types are logically replicated. In general, the logical replication of complex types involves converting a complex type instance from its storage format into a logical representation written in a markup language, like XML. The logical representation is then propagated to a destination (or destinations), which converts the logical representation to a storage format used at the destination for that complex type.

Abstract: 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.