摘要:
Techniques are provided for changing data for an XML construct in an SQL/XML compliant database management system (DBMS). The DBMS allows instances of XML type to represent XML constructs, such as XML documents, XML elements, XML attributes, and fragments of XML documents. An SQL statement is received that includes an XML operator that operates on a particular component in an instance of XML type. During execution of the SQL statement, the XML operator is evaluated by modifying content for the component without modifying the entire instance. For example, an XML delete operator deletes the particular component from the instance. Other XML operators include an insert operator, an insert-before operator, an append-child operator, and an update operator. During execution, these operators may be rewritten to operate on existing SQL constructs, or evaluated by updating only some of the existing SQL constructs, or both.
摘要:
Techniques are provided for changing data for an XML construct in an SQL/XML compliant database management system (DBMS). The DBMS allows instances of XML type to represent XML constructs, such as XML documents, XML elements, XML attributes, and fragments of XML documents. An SQL statement is received that includes an XML operator that operates on a particular component in an instance of XML type. During execution of the SQL statement, the XML operator is evaluated by modifying content for the component without modifying the entire instance. For example, an XML delete operator deletes the particular component from the instance. Other XML operators include an insert operator, an insert-before operator, an append-child operator, and an update operator. During execution, these operators may be rewritten to operate on existing SQL constructs, or evaluated by updating only some of the existing SQL constructs, or both.
摘要:
Techniques for executing database commands include receiving a database command that includes an XML component operation that operates on an XML construct that is based on a first set of one or more relational database constructs. It is determined whether the XML component operation can be transformed to a relational database operation on a particular set of one or more relational database constructs of the first set, which does not involve the XML component operation. If it is determined that the XML component operation can be transformed, then the XML component operation is rewritten as a particular relational database operation that operates on the particular set and that does not involve the XML component operation. The particular relational database operation is evaluated. In another aspect, techniques include determining a primitive set of XML generation operations and replacing non-primitive XML generation operations with one or more operations from the primitive set.
摘要:
Techniques for managing XML data in an SQL compliant DBMS include receiving an SQL statement. The SQL statement includes a particular operator that operates on a first instance of XML type that represents a first set of XML elements. During execution of the SQL statement, the particular operator is evaluated by generating an ordered collection of instances of XML type. Each different instance in the ordered collection is based on a different XML element from the first set; and there is an instance in the ordered collection for every XML element from either the first set or from the first set and its descendents. When descendents are included, each entry in the ordered collection indicates a level in the XML tree. In another aspect, an aggregate operator in the SQL statement operates on a collection of instances, with associated levels, to generate a single instance of XML type.
摘要:
Techniques for transferring a serialized image of data for an XML construct includes selecting a first format from multiple different XML serialization formats that represent, in a database system, data for XML constructs as a series of data units, such as a series of bytes representing characters, or a series of bits, bytes or octets representing binary values. A message is generated that includes a payload and a payload type field. The payload includes particular serialized data that represents particular data for a particular XML construct in the first format. The type field includes data that indicates the first format. The message is sent from a sending component of the database system to a different receiving component of the database system. These techniques allow the format selection to be based on characteristics of the sending or receiving components to make better use of the resources available to the two components.