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Oracle® XML DB Developer's Guide
11g Release 1 (11.1)

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12 PL/SQL APIs for XMLType

This chapter describes the use of the APIs for XMLType in PL/SQL.

This chapter contains these topics:

Overview of PL/SQL APIs for XMLType

This chapter describes the PL/SQL Application Program Interfaces (APIs) for XMLType. These include the following:

API Features

The PL/SQL APIs for XMLType allow you to perform the following tasks:

Lazy Loading of XML Data (Lazy Manifestation)

Because XMLType provides an in-memory or virtual Document Object Model (DOM), it can use a memory conserving process called lazy XML loading, also sometimes referred to as lazy manifestation. This process optimizes memory usage by only loading rows of data when they are requested. It throws away previously-referenced sections of the document if memory usage grows too large. Lazy XML loading supports highly scalable applications that have many concurrent users needing to access large XML documents.

XMLType Data Type Supports XML Schema

The XMLType data type includes support for XML schemas. You can create an XML schema and annotate it with mappings from XML to object-relational storage. To take advantage of the PL/SQL DOM API, first create an XML schema and register it. Then, when you create XMLType tables and columns, you can specify that these conform to the registered XML schema.

XMLType Supports Data in Different Character Sets

XMLType instances can be created from data encoded in any Oracle-supported character set by using the PL/SQL XMLType constructor or XMLType method createXML(). The source XML data must be supplied using data type BFILE or BLOB. The encoding of the data is specified through argument csid. When this argument is zero (0), the encoding of the source data is determined from the XML prolog, as specified in Appendix F of the XML 1.0 Reference.

Method getBLOBVal() retrieves the XML contents in the requested character set.

Caution:

AL32UTF8 is the Oracle Database character set that is appropriate for XMLType data. It is equivalent to the IANA registered standard UTF-8 encoding, which supports all valid XML characters.

Do not confuse Oracle Database database character set UTF8 (no hyphen) with database character set AL32UTF8 or with character encoding UTF-8. Database character set UTF8 has been superseded by AL32UTF8. Do not use UTF8 for XML data. UTF8 supports only Unicode version 3.1 and earlier; it does not support all valid XML characters. AL32UTF8 has no such limitation.

Using database character set UTF8 for XML data could potentially stop a system or affect security negatively. If a character that is not supported by the database character set appears in an input-document element name, a replacement character (usually "?") will be substituted for it. This will terminate parsing and raise an exception. It could cause a fatal error.

PL/SQL DOM API for XMLType (DBMS_XMLDOM)

This section describes the PL/SQL DOM API for XMLType, DBMS_XMLDOM.

See Also:

Oracle Database PL/SQL Packages and Types Reference for descriptions of the individual DBMS_XMLDOM methods

Overview of the W3C Document Object Model (DOM) Recommendation

Skip this section if you are familiar with the generic DOM specifications recommended by the World Wide Web Consortium (W3C).

The Document Object Model (DOM) recommended by the W3C is a universal API for accessing the structure of XML documents. It was originally developed to formalize Dynamic HTML, which is used for animation, interaction, and dynamic updating of Web pages. DOM provides a language-neutral and platform-neutral object model for Web pages and XML documents. DOM describes language-independent and platform-independent interfaces to access and operate on XML components and elements. It expresses the structure of an XML document in a universal, content-neutral way. Applications can be written to dynamically delete, add, and edit the content, attributes, and style of XML documents. DOM makes it possible to create applications that work properly on all browsers, servers, and platforms.

Oracle XDK Extensions to the W3C DOM Standard

Oracle XML Developer's Kit (Oracle XDK) extends the W3C DOM API in various ways. All of these extensions are supported by Oracle XML DB except those relating to client-side operations that are not applicable in the database. This type of procedural processing is available through the SAX interface in the Oracle XDK Java and C components.

Supported W3C DOM Recommendations

All Oracle XML DB APIs for accessing and manipulating XML comply with standard XML processing requirements as approved by the W3C. The PL/SQL DOM supports Levels 1 and 2 from the W3C DOM specifications.

  • In Oracle9i release 1 (9.0.1), Oracle XDK for PL/SQL implemented DOM Level 1.0 and parts of DOM Level 2.0.

  • In Oracle9i release 2 (9.2) and Oracle Database 10g release 1 (10.1), the PL/SQL API for XMLType implements DOM Levels 1.0 and Level 2.0 Core, and is fully integrated in the database through extensions to the XMLType API.

The following briefly describes each level:

  • DOM Level 1.0 – The first formal Level of the DOM specifications, completed in October 1998. Level 1.0 defines support for XML 1.0 and HTML.

  • DOM Level 2.0 – Completed in November 2000, Level 2.0 extends Level 1.0 with support for XML 1.0 with namespaces and adds support for Cascading Style Sheets (CSS) and events (user-interface events and tree manipulation events), and enhances tree manipulations (tree ranges and traversal mechanisms). CSS are a simple mechanism for adding style (fonts, colors, spacing, and so on) to Web documents.

Difference Between DOM and SAX

The generic APIs for XML can be classified in two main categories:

  • Tree-based. DOM is the primary generic tree-based API for XML.

  • Event-based. SAX (Simple API for XML) is the primary generic event-based programming interface between an XML parser and an XML application.

DOM works by creating objects. These objects have child objects and properties, and the child objects have child objects and properties, and so on. Objects are referenced either by moving down the object hierarchy or by explicitly giving an HTML element an ID attribute. For example:

<img src="employee_jdoe.gif" ID="0123jdoe">

Examples of structural manipulations are:

  • Reordering elements

  • Adding or deleting elements

  • Adding or deleting attributes

  • Renaming elements

PL/SQL DOM API for XMLType (DBMS_XMLDOM): Features

Oracle XML DB extends the Oracle Database XML development platform beyond SQL support for storage and retrieval of XML data. It lets you operate on XMLType instances using DOM in PL/SQL, Java, and C.

The default action for the PL/SQL DOM API for XMLType (DBMS_XMLDOM) is to do the following:

  • Produce a parse tree that can be accessed by DOM APIs.

  • Validate, if a DTD is found; otherwise, do not validate.

  • Raise an application error if parsing fails.

DTD validation occurs when the object document is manifested. If lazy manifestation is employed, then the document is validated when it is used.

The PL/SQL DOM API exploits a C-based representation of XML in the server and operates on XML schema-based XML instances. The PL/SQL, Java, and C DOM APIs for XMLType comply with the W3C DOM Recommendations to define and implement structured storage of XML in relational or object-relational columns and as in-memory instances of XMLType. See "Using PL/SQL DOM API for XMLType: Preparing XML Data", for a description of W3C DOM Recommendations.

XML Schema Support

The PL/SQL DOM API for XMLType supports XML schema. Oracle XML DB uses annotations within an XML schema as metadata to determine the structure of an XML document and the mapping of the document to a database schema.

Note:

For backward compatibility and flexibility, the PL/SQL DOM supports both XML schema-based documents and non-schema-based documents.

After an XML schema is registered with Oracle XML DB, the PL/SQL DOM API for XMLType builds an in-memory tree representation of an associated XML document as a hierarchy of node objects, each with its own specialized interfaces. Most node object types can have child node types, which in turn implement additional, more specialized interfaces. Nodes of some node types can have child nodes of various types, while nodes of other node types must be leaf nodes, which do not have child nodes.

Enhanced Performance

Oracle XML DB uses DOM to provide a standard way to translate data between XML and multiple back-end data sources. This eliminates the need to use separate XML translation techniques for the different data sources in your environment. Applications needing to exchange XML data can use a single native XML database to cache XML documents. Oracle XML DB can thus speed up application performance by acting as an intermediate cache between your Web applications and your back-end data sources, whether they are in relational databases or file systems.

Designing End-to-End Applications Using Oracle XDK and Oracle XML DB

When you build applications based on Oracle XML DB, you do not need the additional components in Oracle XDK. However, you can use Oracle XDK components with Oracle XML DB to deploy a full suite of XML-enabled applications that run end-to-end. You can use features in Oracle XDK for:

  • Simple API for XML (SAX) interface processing. SAX is an XML standard interface provided by XML parsers and used by procedural and event-based applications.

  • DOM interface processing, for structural and recursive object-based processing.

Oracle XDK contain the basic building blocks for creating applications that run on a client, in a browser or a plug-in. Such applications typically read, manipulate, transform and view XML documents. To provide a broad variety of deployment options, Oracle XDK is available for Java, C, and C++. Oracle XDK is fully supported and comes with a commercial redistribution license.

Oracle XDK for Java consists of these components:

  • XML Parsers – Creates and parses XML using industry standard DOM and SAX interfaces. Supports Java, C, C++, and JAXP.

  • XSL Processor – Transforms or renders XML into other text-based formats such as HTML. Supports Java, C, and C++.

  • XML Schema Processor – Uses XML simple and complex data types. Supports Java, C, and C++.

  • XML Class Generator, Oracle JAXB Class Generator – Automatically generate C++ and Java classes, respectively, from DTDs and XML schemas, to send XML data from Web forms or applications. Class generators accept an input file and create a set of output classes that have corresponding functionality. For the XML Class Generator, the input file is a DTD, and the output is a series of classes that can be used to create XML documents conforming with the DTD.

  • XML SQL Utility – Generates XML documents, DTDs, and XML schemas from SQL queries. Supports Java.

  • TransX Utility – Loads data encapsulated in XML into the database. Has additional functionality useful for installations.

  • XSQL Servlet – Combines XML, SQL, and XSLT in the server to deliver dynamic Web content.

  • XML Pipeline Processor – Invokes Java processes through XML control files.

  • XSLT VM and Compiler – Provides a high-performance C-based XSLT transformation engine that uses compiled style sheets.

  • XML Java Beans – Parses, transforms, compares, retrieves, and compresses XML documents using Java components.

Using PL/SQL DOM API for XMLType: Preparing XML Data

To prepare data for using PL/SQL DOM APIs in Oracle XML DB:

  1. Create a standard XML schema.

  2. Annotate the XML schema with definitions for the SQL objects you use.

  3. Register the XML schema, to generate the necessary database mappings.

You can then do any of the following:

  • Use XMLType views to wrap existing relational or object-relational data in XML formats, making it available to your applications in XML form. See "Wrapping Existing Data into XML with XMLType Views".

  • Insert XML data into XMLType columns.

  • Use Oracle XML DB PL/SQL and Java DOM APIs to manipulate XML data stored in XMLType columns and tables.

Defining an XML Schema Mapping to SQL Object Types

An XML schema must be registered before it can be referenced by an XML document. When you register an XML schema, elements and attributes it declares are mapped to attributes of corresponding SQL object types within the database.

After XML schema registration, XML documents that conform to the XML schema and reference it can be managed by Oracle XML DB. Tables and columns for storing the conforming documents can be created for root elements defined by the XML schema.

An XML schema is registered by using PL/SQL package DBMS_XMLSCHEMA and by specifying the schema document and its schema-location URL. This URL is a name that uniquely identifies the registered schema within the database; it need not correspond to any real location — in particular, it need not indicate where the schema document is located.

The target namespace of the schema is another URL used in the XML schema. It specifies a namespace for the XML-schema elements and types. An XML document should specify both the namespace of the root element and the schema-location URL identifying the schema that defines this element.

When documents are inserted into Oracle XML DB using path-based protocols such as HTTP(S) and FTP, the XML schema to which the document conforms is registered implicitly, provided its name and location are specified and it has not yet been registered.

See Also:

Oracle Database PL/SQL Packages and Types Reference descriptions of the individual DBMS_XMLSCHEMA methods

DOM Fidelity for XML Schema Mapping

Elements and attributes declared within the XML schema get mapped to separate attributes of the corresponding SQL object type. Other information encoded in an XML document, such as comments, processing instructions, namespace declarations and prefix definitions, and whitespace, is not represented directly.

To store this additional information, binary attribute SYS_XDBPD$ is present in all generated SQL object types. This database attribute stores all information in the original XML document that is not stored using the other database attributes. Retaining this accessory information ensures DOM fidelity for XML documents stored in Oracle XML DB: an XML document retrieved from the database is identical to the original document that was stored.

Note:

In this book, the SYS_XDBPD$ attribute has been omitted from most examples, for simplicity. However, the attribute is always present in SQL object types generated by schema registration.

Wrapping Existing Data into XML with XMLType Views

To make existing relational and object-relational data available to your XML applications, you can create XMLType views, wrapping the data in an XML format. You can then access this XML data using the PL/SQL DOM API.

After you register an XML schema containing annotations that represent the mapping between XML types and SQL object types, you can create an XMLType view that conforms to the XML schema.

DBMS_XMLDOM Methods Supported

All DBMS_XMLDOM methods are supported by Oracle XML DB, with the exception of the following:

  • writeExternalDTDToFile()

  • writeExternalDTDToBuffer()

  • writeExternalDTDToClob()

See Also:

Oracle Database PL/SQL Packages and Types Reference for descriptions of the individual DBMS_XMLDOM methods

PL/SQL DOM API for XMLType: Node Types

In the DOM specification, the term "document" is used to describe a container for many different kinds of information or data, which the DOM objectifies. The DOM specifies the way elements within an XML document container are used to create an object-based tree structure and to define and expose interfaces to manage and use the objects stored in XML documents. Additionally, the DOM supports storage of documents in diverse systems.

When a request such as getNodeType(myNode) is given, it returns myNodeType, which is the node type supported by the parent node. These constants represent the different types that a node can adopt:

  • ELEMENT_NODE

  • ATTRIBUTE_NODE

  • TEXT_NODE

  • CDATA_SECTION_NODE

  • ENTITY_REFERENCE_NODE

  • ENTITY_NODE

  • PROCESSING_INSTRUCTION_NODE

  • COMMENT_NODE

  • DOCUMENT_NODE

  • DOCUMENT_TYPE_NODE

  • DOCUMENT_FRAGMENT_NODE

  • NOTATION_NODE

Table 12-1 shows the node types for XML and HTML and the allowed corresponding children node types.

Table 12-1 XML and HTML DOM Node Types and Their Child Node Types

Node Type Children Node Types
Document

Element (maximum of one), ProcessingInstruction, Comment, DocumentType (maximum of one)

DocumentFragment

Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference

DocumentType

No children

EntityReference

Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference

Element

Element, Text, Comment, ProcessingInstruction, CDATASection, EntityReference

Attr

Text, EntityReference

ProcessingInstruction

No children

Comment

No children

Text

No children

CDATASection

No children

Entity

Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference

Notation

No children


Oracle XML DB DOM API for XMLType also specifies these interfaces:

  • A NodeList interface to handle ordered lists of Nodes, for example:

    • The children of a Node

    • Elements returned by method getElementsByTagName of the element interface

  • A NamedNodeMap interface to handle unordered sets of nodes, referenced by their name attribute, such as the attributes of an element.

Working with XML Schema-Based Data

Oracle Database has several extensions for character-set conversion and input and output to and from a file system. PL/SQL API for XMLType is optimized to operate on XML schema-based XML instances. Function newDOMDocument constructs a DOM document handle, given an XMLType value.

A typical usage scenario would be for a PL/SQL application to:

  1. Fetch or construct an XMLType instance

  2. Construct a DOMDocument node over the XMLType instance

  3. Use the DOM API to access and manipulate the XML data

    Note:

    For DOMDocument, node types represent handles to XML fragments but do not represent the data itself.

    For example, if you copy a node value, DOMDocument clones the handle to the same underlying data. Any data modified by one of the handles is visible when accessed by the other handle. The XMLType value from which the DOMDocument handle is constructed is the data, and reflects the results of all DOM operations on it.

DOM NodeList and NamedNodeMap Objects

NodeList and NamedNodeMap objects in the DOM are active; that is, changes to the underlying document structure are reflected in all relevant NodeList and NamedNodeMap objects.

For example, if a DOM user gets a NodeList object containing the children of an element, and then subsequently adds more children to that element (or removes children, or modifies them), then those changes are automatically propagated in the NodeList, without additional action from the user. Likewise, changes to a node in the tree are propagated throughout all references to that node in NodeList and NamedNodeMap objects.

The interfaces: Text, Comment, and CDATASection, all inherit from the CharacterData interface.

Using PL/SQL DOM API for XMLType (DBMS_XMLDOM)

Figure 12-1 illustrates the use of PL/SQL DOM API for XMLType (DBMS_XMLDOM).

You can create a DOM document (DOMDocument) from an existing XMLType or as an empty document.

  1. The newDOMDocument procedure processes the XMLType instance or empty document. This creates a DOMDocument instance.

  2. You can use DOM API methods such as createElement, createText, createAttribute, and createComment to traverse and extend the DOM tree.

  3. The results of methods such as DOMElement and DOMText can also be passed to makeNode to obtain the DOMNode interface.

Figure 12-1 Using PL/SQL DOM API for XMLType

Description of Figure 12-1 follows
Description of "Figure 12-1 Using PL/SQL DOM API for XMLType"

PL/SQL DOM API for XMLType – Examples

This section presents examples of using the PL/SQL DOM API for XMLType.

Remember to call procedure freeDocument for each DOMDocument instance, when you are through with the instance. This procedure frees the document and all of its nodes. You can still access XMLType instances on which DOMDocument instances were built, even after the DOMDocument instances have been freed.

Example 12-1 Creating and Manipulating a DOM Document

This example creates a hierarchical, in-memory representation of an XML document – a DOM document. It uses a handle to this DOM document to manipulate it: print it, change part of it, and print it again after the change. Manipulating the DOM document by its handle also indirectly affects the XML data represented by the document, so that querying that data after the change shows the changed result.

The in-memory document is created from an XMLType variable using PL/SQL function newDOMDocument. The handle to this document is created using function makeNode. The document is written to a VARCHAR2 buffer using function writeToBuffer, and the buffer is printed using DBMS_OUTPUT.put_line.

After manipulating the document using various DBMS_XMLDOM procedures, the (changed) data in the XMLType variable is inserted into a table and queried, showing the change. It is only when the data is inserted into a database table that it becomes persistent; until then, it exists in memory only. This persistence is demonstrated by the fact that the database query is made after the in-memory document (DOMDocument instance) has been freed.

CREATE TABLE person OF XMLType;

DECLARE 
  var       XMLType; 
  doc       DBMS_XMLDOM.DOMDocument; 
  ndoc      DBMS_XMLDOM.DOMNode; 
  docelem   DBMS_XMLDOM.DOMElement;
  node      DBMS_XMLDOM.DOMNode; 
  childnode DBMS_XMLDOM.DOMNode; 
  nodelist  DBMS_XMLDOM.DOMNodelist;
  buf       VARCHAR2(2000);
BEGIN 
  var := XMLType('<PERSON><NAME>ramesh</NAME></PERSON>');

  -- Create DOMDocument handle
  doc     := DBMS_XMLDOM.newDOMDocument(var); 
  ndoc    := DBMS_XMLDOM.makeNode(doc);

  DBMS_XMLDOM.writeToBuffer(ndoc, buf);
  DBMS_OUTPUT.put_line('Before:'||buf);

  docelem := DBMS_XMLDOM.getDocumentElement(doc);

  -- Access element
  nodelist := DBMS_XMLDOM.getElementsByTagName(docelem, 'NAME');
  node := DBMS_XMLDOM.item(nodelist, 0);
  childnode := DBMS_XMLDOM.getFirstChild(node);

  -- Manipulate element
  DBMS_XMLDOM.setNodeValue(childnode, 'raj');
  DBMS_XMLDOM.writeToBuffer(ndoc, buf);
  DBMS_OUTPUT.put_line('After:'||buf);
  DBMS_XMLDOM.freeDocument(doc);
  INSERT INTO person VALUES (var);
END;
/

This produces the following output:

Before:<PERSON>
  <NAME>ramesh</NAME>
</PERSON>
 
After:<PERSON>
  <NAME>raj</NAME>
</PERSON>

This query confirms that the data has changed:

SELECT * FROM person;
SYS_NC_ROWINFO$
---------------
<PERSON>
  <NAME>raj</NAME>
</PERSON>
 
1 row selected.

Example 12-2 Creating an Element Node and Obtaining Information About It

This example creates an empty DOM document, and then adds an element node (<ELEM>) to the document. DBMS_XMLDOM API node procedures are used to obtain the name (<ELEM>), value (NULL), and type (1 = element node) of the element node.

DECLARE
  doc   DBMS_XMLDOM.DOMDocument;
  elem  DBMS_XMLDOM.DOMElement;
  nelem DBMS_XMLDOM.DOMNode;
BEGIN
  doc := DBMS_XMLDOM.newDOMDocument;
  elem := DBMS_XMLDOM.createElement(doc, 'ELEM');
  nelem := DBMS_XMLDOM.makeNode(elem);
  DBMS_OUTPUT.put_line('Node name = ' || DBMS_XMLDOM.getNodeName(nelem));
  DBMS_OUTPUT.put_line('Node value = '|| DBMS_XMLDOM.getNodeValue(nelem));
  DBMS_OUTPUT.put_line('Node type = ' || DBMS_XMLDOM.getNodeType(nelem));
  DBMS_XMLDOM.freeDocument(doc);
END;
/

This produces the following output:

Node name = ELEM
Node value =
Node type = 1

Large Node Handling Using DBMS_XMLDOM

Prior to Oracle Database 11g Release 1 (11.1), each text node or attribute value processed by Oracle XML DB was limited in size to 64 K bytes. Starting with release 11.1, this restriction no longer applies.

To overcome this size limitation and allow nodes to contain graphics files, PDF files, and multibyte character encodings, the following abstract streams are available. These abstract PL/SQL streams are analogous to the corresponding Java streams. Each input stream has an associated writer, or data producer, and each output stream has an associated reader, or data consumer.

  1. Binary Input Stream: This provides the data consumer with read-only access to source data, as a sequential (non-array) linear space of bytes. The consumer has iterative read access to underlying source data (whatever representation) in binary format, that is, read access to source data in unconverted, "raw" format. The consumer sees a sequence of bytes as they exist in the node. There is no specification of the format or representation of the source data. In particular, there is no associated character set.

  2. Binary Output Stream: This provides the data producer with write-only access to target data as a sequential (non-array) linear space of bytes. The producer has iterative write access to target data in binary format, that is, write access to target data in pure binary format with no data semantic at all. The producer passes a sequence of bytes and the target data is replaced by these bytes. No data conversion occurs.

  3. Character Input Stream: This provides the data consumer iterative read-only access to source data as a sequential (non-array) linear space of characters, independent of the representation and format of the source data. Conversion of the source data may or may not occur.

  4. Character Output Stream: This provides the data producer with iterative write-only access to target data as a sequential (non-array) linear space of characters. The producer passes a sequence of characters and the target data is replaced by this sequence of characters. Conversion of the passed data may or may not occur.

Each of the input streams has the following abstract methods: open, read, and close. Each of the output streams has the following abstract methods: open, write, flush, and close. For output streams, you must close the stream before any nodes are physically written.

There are four general node access models, for reading and writing. Each access model has both binary and character versions. Binary and character stream methods defined on data type DOMNode realize these access models. Each access model is described in a separate section, with an explanation of the PL/SQL functions and procedures in package DBMS_XMLDOM that operate on large nodes.

For all except the get-push and set-pull access models (whether binary or character), Oracle supplies a concrete stream that you can use (implicitly). For get-push and set-pull, you must define a subtype of the abstract stream type that Oracle provides, and you must implement its access methods (open, close, and so on). For get-push and set-pull, you then instantiate your stream type and supply your stream as an argument to the access method. So, for example, you would use my_node.getNodeValueAsCharacterStream(my-stream) for get-push, but just my_node.getNodeValueAsCharacterStream() for get-pull. The latter requires no explicit stream argument, because the concrete stream supplied by Oracle is used.

Note:

When you access a character-data stream, the access method you use determines the apparent character set of the nodes accessed. If you use Java to access the stream, then the character set seen by your Java program is UCS2 (or an application-specified character set). If you use PL/SQL to access the stream, then the character set seen by your PL/SQL program is the database-session character set (or an application-specified character set). In all cases, however, the XML data is stored in the database in the database character set.

In the following descriptions, C1 is the character set of the node as stored in the database, and C2 is the character set of the node as seen by your program.

See Also:

Get-Push Model

To read a node value in this model, the application creates a binary output stream or character output stream and passes this to Oracle XML DB. In this case, the source data is the node value. Oracle XML DB will populate the output stream by pushing node data into the stream. If the stream is a character output stream, then the character set, C2, will be the session character set and node data is converted, if necessary, from C1 to C2. Additionally, the data type of the node may be any supported by Oracle XML DB and, if the node data type is not character data then the node data is first converted to character data in C2. If a binary output stream, the data type of the node must be RAW or BLOB.

The procedures of the DBMS_XMLDOM package to be used for this case are:

PROCEDURE getNodeValueAsBinaryStream (n IN DBMS_XMLDOM.domnode, 
          value IN SYS.utl_BinaryOutputStream);

The application passes an implementation of SYS.utl_BinaryOutputStream into which Oracle XML DB will write the contents of the node. The data type of the node must be RAW or CLOB; if not an exception is raised.

PROCEDURE getNodeValueAsCharacterStream (n IN DBMS_XMLDOM.domnode,
          value IN SYS.utl_CharacterOutputStream);

The node data is converted, as necessary, to the session character set and then "pushed" into the SYS.utl_CharacterOutputStream.

The following example fragments illustrate reading the node value as binary data and driving the write methods in a user-defined subtype of SYS.utl_BinaryOutPutStream, which is called MyBinaryOutputStream:

Example 12-3 Creating a User-Defined Subtype of SYS.util_BinaryOutputStream()

CREATE TYPE MyBinaryOutputStream UNDER SYS.utl_BinaryOutputStream (
    CONSTRUCTOR FUNCTION MyBinaryOutputStream ()
    RETURN SELF AS RESULT,
    MEMBER FUNCTION  write (bytes IN RAW) RETURN INTEGER,
    MEMBER PROCEDURE write (bytes IN RAW, offset IN INTEGER, length IN OUT 
           INTEGER),
    MEMBER FUNCTION flush () RETURN BOOLEAN,
    MEMBER FUNCTION close () RETURN BOOLEAN);
);

-- Here, you write the code to implement these methods
...

Example 12-4 Retrieving Node Value with a User-Defined Stream

DECLARE
  ostream     MyBinaryOutputStream = MyBinaryOutputStream ();
  node        DBMS_XMLDOM.domnode;
  ...
BEGIN
  ...
  -- This drives the write methods in MyBinaryOutputStream,
  -- flushes the data, and closes the stream after the value has been
  -- completely written.
  DBMS_XMLDOM.getNodeValueAsBinaryStream (node, ostream);
  ...
END;

Get-Pull Model

To read the value of a node in this model, Oracle XML DB creates a binary input stream or character input stream and returns this to the caller. The character set, C2, of the character input stream is the current session character set. Oracle XML DB will populate the input stream as the caller pulls the node data from the stream so Oracle XML DB is again the producer of the data. If the stream is a character input stream, then the node data type may be any supported by Oracle XML DB and node data, if character, is converted, if necessary, from C1 to C2. If the node data is non-character, it is converted to character in C2. If a binary input stream, the data type of the node must be RAW or BLOB.

The functions of the DBMS_XMLDOM package to be used for this case are getNodeValueAsBinaryStream and getNodeValueAsCharacterStream.

FUNCTION getNodeValueAsBinaryStream(n IN DBMS_XMLDOM.domnode) 
         RETURN SYS.utl_BinaryInputStream;

This function returns an instance of the new PL/SQL SYS.utl_BinaryInputStream that can be read using defined methods as described in the section "Set-Pull Model". The node data type must be RAW or BLOB; otherwise, an exception is raised.

FUNCTION getNodeValueAsCharacterStream (n IN DBMS_XMLDOM.domnode) 
         RETURN SYS.utl_CharacterInputStream;

This function returns an instance of the new PL/SQL SYS.utl_CharacterInputStream that can be read using defined methods. If the node data is character it is converted to the current session character set. If the node data is not character data, it is first converted to character data.

Example 12-5 illustrates reading a node value as binary data in 50-byte increments:

Example 12-5 Get-Pull of Binary Data

DECLARE
  istream      SYS.utl_BinaryInputStream;
  node         DBMS_XMLDOM.domnode;
  buffer       raw(50);
  numBytes     pls_integer;
  ...
BEGIN
  ...
  istream := DBMS_XMLDOM.getNodeValueAsBinaryStream (node);
  -- Read stream in 50-byte chunks
  LOOP
    numBytes := 50;
    istream.read ( buffer, numBytes);
    if numBytes <= 0 then
       exit;
    end if;
-- Process next 50 bytes of node value in buffer
END LOOP
...
END;

Example 12-6 illustrates reading a node value as character data in 50-character increments:

Example 12-6 Get-Pull of Character Data

DECLARE
  istream      SYS.utl_CharacterInputStream;
  node         DBMS_XMLDOM.domnode;
  buffer       varchar2(50);
  numChars     pls_integer;
  ...
BEGIN
  ...
  istream := DBMS_XMLDOM.getNodeValueAsCharacterStream (node);
-- Read stream in 50-character chunks
LOOP
   numChars := 50;
   istream.read ( buffer, numChars);
   IF numChars <= 0 then
      exit;
   END IF;
-- Process next 50 characters of node value in buffer
END LOOP 
...
END;

Set-Pull Model

To write a node value in this mode, the application creates a binary input stream or character input stream and passes this to Oracle XML DB. The character set of the character input stream, C2, is the session character set. Oracle XML DB will pull the data from the input stream and populate the node. If the stream is a character input stream, then the data type of the node may be any supported by Oracle XML DB. If the data type of the node is not character, the stream data is first converted to the node data type. If the node data type is character, then no conversion occurs; the node data remains in character set C2. If the stream is a binary input stream, then the data type of the node must be RAW or BLOB and no conversion occurs.

The procedures of the DBMS_XMLDOM package to be used for this case are setNodeValueAsBinaryStream and setNodeValueAsCharacterStream.

PROCEDURE setNodeValueAsBinaryStream(n IN DBMS_XMLDOM.domnode,
          value IN SYS.utl_BinaryInputStream);

The application passes in an implementation of SYS.utl_BinaryInputStream from which Oracle XML DB reads data to populate the node. The data type of the node must be RAW or BLOB; if not an exception is raised.

PROCEDURE setNodeValueAsCharacterStream (n IN DBMS_XMLDOM.domnode,
          value IN SYS.utl_CharacterInputStream);

The application passes in an implementation of SYS.utl_CharacterInputStream from which Oracle XML DB reads to populate the node. The data type of the node may be any valid type supported by Oracle XML DB. If it is a non-character data type, the character data read from the stream is converted to the data type of the node. If the data type of the node is either character or CLOB, then no conversion occurs and the character set of the node becomes the character set of the PL/SQL session.

Example 12-7 illustrates setting the node value to binary data produced by the read methods defined in a user-defined subtype of SYS.utl_BinaryInputStream, which is called MyBinaryInputStream:

Example 12-7 Set-Pull of Binary Data

CREATE TYPE MyBinaryInputStream UNDER SYS.utl_BinaryInputStream (
    CONSTRUCTOR FUNCTION MyBinaryInputStream ()
    RETURN SELF AS RESULT,
  MEMBER FUNCTION read () RETURN RAW,
  MEMBER PROCEDURE read (bytes IN OUT RAW, numbytes IN OUT INTEGER),
  MEMBER PROCEDURE read (bytes IN OUT RAW, offset IN INTEGER, length IN OUT
         INTEGER),
  MEMBER FUNCTION close () RETURN BOOLEAN);

You can use an object of type MyBinaryInputStream to set the value of a node as follows:

DECLARE
  istream     MyBinaryInputStream = MyBinaryInputStream ();
  node        DBMS_XMLDOM.domnode;
  ...
BEGIN
  ...
  -- This drives the read methods in MyBinaryInputStream
  DBMS_XMLDOM.setNodeValueAsBinaryStream (node, istream);
  ...
END;

Set-Push Model

To write a new node value in this mode, Oracle XML DB creates a binary output stream or character output stream and returns this to the caller. The character set of the character output stream, C2, is the current session character set. The caller pushes data into the output stream and Oracle XML DB then writes this to the Oracle XML DB Node. If the stream is a character output stream, then the data type of the node may be any type supported by Oracle XML DB. In this case, the character data is converted to the node data type. If the node data type is character, then the character set, C1, is changed to C2. No data conversion occurs. If the stream is a binary input stream, and the data type of the node must be RAW or BLOB. In this case, the stream is read without data conversion.

The procedures of the DBMS_XMLDOM package to be used for this case are setNodeValueAsBinaryStream and setNodeValueAsCharacterStream.

FUNCTION setNodeValueAsBinaryStream(n IN DBMS_XMLDOM.domnode) 
         RETURN SYS.utl_BinaryOutputStream;

This function returns an instance of SYS.utl_BinaryOutputStream into which the caller can write the node value. The data type of the node must be RAW or BLOB; if not, an exception is raised.

FUNCTION setNodeValueAsCharacterStream (n IN DBMS_XMLDOM.domnode) 
         RETURN SYS.utl_CharacterOutputStream;

This function returns an instance of the PL/SQL SYS.utl_CharacterOutputStream type into which the caller can write the node value. The data type of the node can be any valid Oracle XML DB data type. If the type is not character or CLOB, the character data written to the stream is converted to the node data type. If the data type of the node is character or CLOB, then the character data written to the stream is converted from PL/SQL session character set to the character set of the node

Example 12-8 illustrates setting the value of a node to binary data by writing 50-byte segments into the SYS.utl_BinaryOutputStream:

Example 12-8 Set-Push of Binary Data

DECLARE
  ostream      SYS.utl_BinaryOutputStream;
  node         DBMS_XMLDOM.domnode;
  buffer       raw(500);
  segment      raw(50);
  numBytes     pls_integer;
  offset       pls_integer;
  ...
BEGIN
  ...
  ostream := DBMS_XMLDOM.setNodeValueAsBinaryStream (node);
  offset := 0;
  length := 500;
  -- Write to stream in 50-byte chunks
  LOOP
    numBytes := 50;
    -- Get next 50 bytes of buffer
    ostream.write ( segment, offset, numBytes);
    length := length - numBytes;
    IF length  <= 0 then
       exit;
    END IF;
  END LOOP
  ostream.close();
  ...
END;

Determining Binary Stream or Character Stream

To determine whether to use a character stream or a binary stream to access the node value use the following method which is also included as part of the DBMS_XMLDOM package:

FUNCTION useBinaryStream (n IN DBMS_XMLDOM.domnode) RETURN BOOLEAN;

This function returns TRUE if the data type of the node is RAW or BLOB, so that the node value may be read or written using either a SYS.utl_BinaryInputStream or a SYS.utl_BinaryOutputStream. If a value of FALSE is returned, the node value can be accessed only using a SYS.utl_CharacterInputStream or a SYS.utl_CharacterOutputStream.

PL/SQL Parser API for XMLType (DBMS_XMLPARSER)

XML documents are made up of storage units, called entities, that contain either parsed or unparsed data. Parsed data is made up of characters, some of which form character data and some of which form markup. Markup encodes a description of the document storage layout and logical structure. XML provides a mechanism for imposing constraints on the storage layout and logical structure.

A software module called an XML parser or processor reads XML documents and provides access to their content and structure. An XML parser usually does its work on behalf of another module, typically the application.

PL/SQL Parser API for XMLType: Features

The PL/SQL Parser API for XMLType (DBMS_XMLPARSER) builds a result tree that can be accessed by PL/SQL APIs. If parsing fails, it raises an error.

See Oracle Database PL/SQL Packages and Types Reference for descriptions of the individual methods of the PL/SQL Parser API for XMLType (DBMS_XMLPARSER).

Method DBMS_XMLPARSER.setErrorLog() is not supported.

Using PL/SQL Parser API for XMLType (DBMS_XMLPARSER)

Figure 12-2 illustrates how to use the PL/SQL Parser for XMLType (DBMS_XMLPARSER). These are the steps:

  1. Construct a parser instance using method.

  2. Parse XML documents using methods such as parseBuffer(), parseClob(), and parse(URI). An error is raised if the input is not a valid XML document.

  3. Call getDocument on the parser to obtain a DOMDocument interface.

Figure 12-2 Using PL/SQL Parser API for XMLType

Description of Figure 12-2 follows
Description of "Figure 12-2 Using PL/SQL Parser API for XMLType"

Example 12-9 Parsing an XML Document

This example parses a simple XML document. It creates an XML parser (instance of DBMS_XMLPARSER.parser) and uses it to parse the XML document (text) in variable indoc. Parsing creates a DOM document, which is retrieved from the parser using DBMS_XMLPARSER.getDocument. A DOM node is created that contains the entire document, and the node is printed. After freeing (destroying) the DOM document, the parser instance is freed using DBMS_XMLPARSER.freeParser.

DECLARE
  indoc    VARCHAR2(2000);
  indomdoc DBMS_XMLDOM.DOMDocument;
  innode   DBMS_XMLDOM.DOMNode;
  myparser DBMS_XMLPARSER.parser;
  buf      VARCHAR2(2000);
BEGIN
  indoc := '<emp><name>De Selby</name></emp>';
  myParser := DBMS_XMLPARSER.newParser;
  DBMS_XMLPARSER.parseBuffer(myParser, indoc);
  indomdoc := DBMS_XMLPARSER.getDocument(myParser);
  innode := DBMS_XMLDOM.makeNode(indomdoc);
  DBMS_XMLDOM.writeToBuffer(innode, buf);
  DBMS_OUTPUT.put_line(buf);
  DBMS_XMLDOM.freeDocument(indomdoc);
  DBMS_XMLPARSER.freeParser(myParser);
END;
/

This produces the following output:

<emp><name>De Selby</name></emp>

PL/SQL XSLT Processor for XMLType (DBMS_XSLPROCESSOR)

The W3C XSL Recommendation describes rules for transforming a source tree into a result tree. A transformation expressed in Extensible Stylesheet Language Transformation (XSLT) language is called an XSL style sheet. The transformation specified is achieved by associating patterns with templates defined in the XSLT style sheet. A template is instantiated to create part of the result tree.

Enabling Transformations and Conversions with XSLT

The Oracle XML DB PL/SQL DOM API for XMLType also supports XSLT. This enables transformation from one XML document to another, or conversion into HTML, PDF, or other formats. XSLT is also widely used to convert XML to HTML for browser display.

The embedded XSLT processor follows Extensible Stylesheet Language (XSL) statements and traverses the DOM tree structure for XML data residing in XMLType. Oracle XML DB applications do not require a separate parser as did the prior release XML Parser for PL/SQL. However, applications requiring external processing can still use the XML Parser for PL/SQL first to expose the document structure.

PL/SQL package DBMS_XSLPROCESSOR provides a convenient and efficient way of applying a single style sheet to multiple documents. The performance of this package is better than that of SQL function transform and XMLType method transform(), because the style sheet is parsed only once.

Note:

The XML Parser for PL/SQL in Oracle XDK parses an XML document (or a standalone DTD) so that the XML document can be processed by an application, typically running on the client. PL/SQL APIs for XMLType are used for applications that run on the server and are natively integrated in the database. Benefits include performance improvements and enhanced access and manipulation options.

PL/SQL XSLT Processor for XMLType: Features

PL/SQL XSLT Processor for XMLType (DBMS_XSLPROCESSOR) is the Oracle XML DB implementation of the XSL processor. This follows the W3C XSLT final recommendation (REC-xslt-19991116). It includes the required action of an XSL processor in terms of how it must read XSLT style sheets and the transformations it must achieve.

The types and methods of the PL/SQL XSLT Processor API are made available by the PL/SQL package, DBMS_XSLPROCESSOR. The methods in this package use two PL/SQL data types specific to the XSL Processor implementation: PROCESSOR and STYLESHEET.

All DBMS_XSLPROCESSOR methods are supported by Oracle XML DB, with the exception of method setErrorLog().

See Also:

Oracle Database PL/SQL Packages and Types Reference for descriptions of the individual DBMS_XSLPROCESSOR methods

Using PL/SQL XSLT Processor API for XMLType (DBMS_XSLPROCESSOR)

Figure 12-3 illustrates how to use XSLT Processor for XMLType (DBMS_XSLPROCESSOR). These are the steps:

  1. Construct an XSLT processor using newProcessor.

  2. Use newStylesheet to build a STYLESHEET object from a DOM document.

  3. Optionally, you can set parameters for the STYLESHEET object using setParams.

  4. Use processXSL to transform a DOM document using the processor and STYLESHEET object.

  5. Use the PL/SQL DOM API for XMLType to manipulate the result of XSLT processing.

Figure 12-3 Using PL/SQL XSLT Processor for XMLType

Description of Figure 12-3 follows
Description of "Figure 12-3 Using PL/SQL XSLT Processor for XMLType"

Example 12-10 Transforming an XML Document Using an XSL Style Sheet

This example transforms an XML document using procedure processXSL. It uses the same parser instance to create two different DOM documents: the XML text to transform and the XSLT style sheet. An XSL processor instance is created, which applies the style sheet to the source XML to produce a new DOM fragment. A DOM node (outnode) is created from this fragment, and the node content is printed. The output DOM fragment, parser, and XSLT processor instances are freed using procedures freeDocFrag, freeParser, and freeProcessor, respectively.

DECLARE
  indoc      VARCHAR2(2000);
  xsldoc     VARCHAR2(2000);
  myParser   DBMS_XMLPARSER.parser;
  indomdoc   DBMS_XMLDOM.DOMDocument;
  xsltdomdoc DBMS_XMLDOM.DOMDocument;
  xsl        DBMS_XSLPROCESSOR.stylesheet;
  outdomdocf DBMS_XMLDOM.DOMDocumentFragment;
  outnode    DBMS_XMLDOM.DOMNode;
  proc       DBMS_XSLPROCESSOR.processor;
  buf        VARCHAR2(2000);
BEGIN
  indoc := '<emp><empno>1</empno> 
              <fname>robert</fname> 
              <lname>smith</lname>
              <sal>1000</sal>
              <job>engineer</job>
            </emp>';
  xsldoc := '<?xml version="1.0"?> 
             <xsl:stylesheet version="1.0"     
                             xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
               <xsl:output encoding="utf-8"/>
               <!-- alphabetizes an xml tree -->
               <xsl:template match="*">
                 <xsl:copy>
                   <xsl:apply-templates select="*|text()">
                     <xsl:sort select="name(.)" data-type="text" 
                               order="ascending"/>
                   </xsl:apply-templates>
                 </xsl:copy>
               </xsl:template>
               <xsl:template match="text()">
                 <xsl:value-of select="normalize-space(.)"/>
               </xsl:template>
             </xsl:stylesheet>';
  myParser := DBMS_XMLPARSER.newParser;
  DBMS_XMLPARSER.parseBuffer(myParser, indoc);
  indomdoc   := DBMS_XMLPARSER.getDocument(myParser);
  DBMS_XMLPARSER.parseBuffer(myParser, xsldoc);
  xsltdomdoc := DBMS_XMLPARSER.getDocument(myParser);
  xsl        := DBMS_XSLPROCESSOR.newStyleSheet(xsltdomdoc, '');
  proc       := DBMS_XSLPROCESSOR.newProcessor;
  --apply stylesheet to DOM document   
  outdomdocf := DBMS_XSLPROCESSOR.processXSL(proc, xsl, indomdoc);
  outnode    := DBMS_XMLDOM.makeNode(outdomdocf); 
  -- PL/SQL DOM API for XMLType can be used here
  DBMS_XMLDOM.writeToBuffer(outnode, buf);
  DBMS_OUTPUT.put_line(buf);
  DBMS_XMLDOM.freeDocument(indomdoc);
  DBMS_XMLDOM.freeDocument(xsltdomdoc);
  DBMS_XMLDOM.freeDocFrag(outdomdocf);
  DBMS_XMLPARSER.freeParser(myParser);
  DBMS_XSLPROCESSOR.freeProcessor(proc);
END;
/

This produces the following output:

<emp>
<empno>1</empno>
<fname>robert</fname>
<job>engineer</job>
<lname>smith</lname>
<sal>1000</sal>
</emp>

PL/SQL Translation API for XMLType (DBMS_XMLTRANSLATIONS)

When you store security objects in the Oracle XML DB Repository, you store them as XMLType instances. The security objects also contain some strings that need to be translated, so that you can search for or display them in various languages. The translations for these strings are also stored in the Oracle XML DB Repository, along with the original strings, because they must be associated with the original document. You can retrieve and operate on these strings, depending on your language settings.

Oracle XML DB provides translation support through the DBMS_XMLTRANSLATIONS package, which provides an interface to perform translations so that strings can be searched or displayed in various languages.

See Also:

Chapter 6, "XML Schema Storage and Query: Basic" for an overview of XML translations

DBMS_XMLTRANSLATIONS Methods

The DBMS_XMLTRANSLATIONS package provides the following methods:

  • updateTranslation: Updates the translation in a particular language at the specified XPATH. If the translation in that language is not present, then it is inserted.

  • setSourceLang: Sets the source language to a particular language at the specified XPATH.

  • translateXML: Returns the document in the specified language.

  • getBaseDocument: Returns the base document with all the translations.

  • extractXLiff: Extracts the translations in XLIFF format from either an XMLTYPE instance or a resource in Oracle XML DB Repository.

  • mergeXLiff: Merges the translations in XLIFF format into either an XMLTYPE or a resource in Oracle XML DB Repository.

  • disableTranslation: Disables translations in the current session so that query or retrieval will take place on the base document ignoring session language values.

  • enableTranslation: Enables translations in the current session.

See Also:

Oracle Database PL/SQL Packages and Type References for a description of the individual DBMS_XMLTRANSLATIONS methods.