XMLType is a predefined type for representing XML entities as
UDT objects. This is compatible with Oracle9i and later. You can
get better performance and flexibility by using use plain built-in
functions that directly operate with XML entities. All predefined
member functions of XMLType for extracting fragments from an
XMLType are actually wrappers for
xpath_eval() built-in function. You can
declare a column of XMLType but the actual type of the created
column will be "LONG XML". Thus any XML-related feature that can be
used for "LONG XML" column will work with XMLType. E.g. WITH SCHEMA constraint
allows you to force stored values to match a particular schema;
XML free text index can
accelerate search for documents by content etc.
XMLType behaves like any user-defined type, with the only difference in type conversion rules. If an XML entity is passed as an argument instead of an instance of XMLType, a new instance of XMLType is created by a constructor that takes the entity as an argument. Similarly, functions that accept XML entities as arguments can also accept an instance of XMLType as an actual value of argument.
The following example creates a table with an XMLType column, put two records there and performs a simple search:
CREATE TABLE Xml_tab ( xmlval XMLType); INSERT INTO Xml_tab VALUES ( xmltype('<?xml version="1.0"?> <EMP> <EMPNO>221</EMPNO> <ENAME>John</ENAME> </EMP>')); INSERT INTO Xml_tab VALUES ( xmltype('<?xml version="1.0"?> <PO> <PONO>331</PONO> <PONAME>PO_1</PONAME> </PO>')); -- now extract the numerical values for the employee numbers SELECT e.xmlval.extract('//EMPNO/text()').getNumVal() as empno FROM Xml_tab WHERE e.xmlval.existsnode('/EMP/EMPNO') = 1;
Virtuoso can perform XPATH search in XMLType instances:
member functions are convenient for simple searches and any
built-in XPATH functions like
xquery_eval() can handle XMLType parameters
instead of XML entity parameters. An application can use
member functions to convert found node to strings, numbers or an
XML source text of the node.
Instances of the type can store the URL of the XML schema to
which they should conform. This URL can be specified when an
instance is constructed; Once an instance is created, its schema
URL cannot be changed but a modified copy can be created by
createNonSchemaBasedXML() member functions;
getSchemaURL() member functions check whether
the given instance is schema based or not and what particular
schema is used.
An schema based XMLType instance can be validated against its
schema; If it has been validated against its schema once with no
errors detected then a special "VALIDATED" flag is set in the
instance indicating that there is no need to validate it again.
schemaValidate() member function performs the
isSchemaValidated() queries the "VALIDATED"
setSchemaValidated() changes the "VALIDATED"
flag if application needs optimization tricks.
In addition, any instance can be validated against an arbitrary
schema via member function
isSchemaValid() . Built-in function
xml_validate_schema() may accept
instance of XMLType as its first argument, providing even more