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DBMS_XMLDOM

Use DBMS_XMLDOM to access XMLType objects. You can access both schema-based and nonschema-based documents. Before database startup, you must specify the read-from and write-to directories in the initialization.ORA file; for example:

UTL_FILE_DIR=/mypath/insidemypath

The read-from and write-to files must be on the server file system.

This chapter details the following:

• Types of DBMS_XMLDOM
• Defined Constants of DBMS_XMLDOM
• Exceptions of DBMS_XMLDOM
• Functions and Procedures of DBMS_XMLDOM

Description of DBMS_XMLDOM

The Document Object Model (DOM) is an application programming interface (API) for HTML and XML documents. It defines the logical structure of documents and the way a document is accessed and manipulated. In the DOM specification, the term "document" is used in the broad sense. XML is increasingly being used as a way of representing many different kinds of information that may be stored in diverse systems, and much of this would traditionally be seen as data rather than as documents. Nevertheless, XML presents this data as documents, and the DOM may be used to manage this data.

With the Document Object Model, programmers can build documents, navigate their structure, and add, modify, or delete elements and content. Anything found in an HTML or XML document can be accessed, changed, deleted, or added using the Document Object Model, with a few exceptions. In particular, the DOM interfaces for the XML internal and external subsets have not yet been specified.

One important objective of the W3C specification for the Document Object Model is to provide a standard programming interface that can be used in a wide variety of environments and applications. The DOM is designed to be used with any programming language. Since the DOM standard is object-oriented, for this PL/SQL adaptation, some changes had to be made:

• Various DOM interfaces such as Node, Element, etc. have equivalent PL/SQL types DOMNode, DOMElement, etc. respectively.
• Various DOMException codes such as WRONG_DOCUMENT_ERR, HIERARCHY_REQUEST_ERR, etc. have similarly named PL/SQL exceptions
• Various DOM Node type codes such as ELEMENT_NODE, ATTRIBUTE_NODE, etc. have similarly named PL/SQL constants
• Methods defined on a DOM type become functions or procedures that accept it as a parameter. For example, to perform appendChild on a DOM Node n, the appendChild() PL/SQL function is provided,

          FUNCTION appendChild( n DOMNode, 
                                 newChild IN DOMNode)
                                 RETURN DOMNode;
  
  

  and to perform setAttribute on a DOM Element elem, the setAttribute() PL/SQL procedure is provided:

              PROCEDURE setAttribute( elem DOMElement,
                                      name IN VARCHAR2,
                                      value IN VARCHAR2); 
  
  

DOM defines an inheritance hierarchy. For example, Document, Element, and Attr are defined to be subtypes of Node. Thus, a method defined in the Node interface should be available in these as well. Since, such inheritance is not directly possible in PL/SQL, the makeNode functions need to be invoked on different DOM types to convert these into a DOMNode. The appropriate functions or procedures that accept DOMNodes can then be called to operate on these types. If, subsequently, type specific functionality is desired, the DOMNode can be converted back into the type by using the make*() functions, where DOM* is the desired DOM type.

The implementation of this PL/SQL DOM interface followed the DOM standard of revision REC-DOM-Level-1-19981001. The types and methods described in this document are made available by the PL/SQL package DBMS_XMLDOM.

• Before database startup, the read-from and write-to directories in the initialization.ORA file must be specified; for example:

            UTL_FILE_DIR=/mypath/insidemypath
  

• The read-from and write-to files must be on the server file system.