Skip Headers

Oracle9i XML Database Developer's Guide - Oracle XML DB
Release 2 (9.2)

Part Number A96620-02
Go to Documentation Home
Go to Book List
Book List
Go to Table of Contents
Go to Index
Go to Master Index
Master Index
Go to Feedback page

Go to previous page Go to next page
View PDF

Creating and Accessing Data Through URLs

This chapter describes how to generate and store URLs inside the database and to retrieve the data pointed to by the URLs. It also introduces the concept of DBUris which are URLs to relational data stored inside the database. It explains how to create and store references to data stored in Oracle XML DB Repository hierarchy.

This chapter contains these sections:

How Oracle9i Database Works with URLs and URIs

In developing Internet applications, and particularly Internet-based XML applications, you often need to refer to data somewhere on a network using URLs or URIs.

Oracle9i can represent various kinds of paths within the database. Each corresponds to a different object type, all derived from a general type called UriType:

Accessing and Processing Data Through HTTP

Any resources stored inside ORACLE XML DB Repository can also be retrieved by using the HTTP Server in Oracle XML DB. Oracle9i also includes a servlet that makes table data available through HTTP URLs. The data can be returned as plain text, HTML, or XML.

Any Web-enabled client or application can use the data without SQL programming or any specialized database API. You can retrieve the data by linking to it in a Web page or by requesting it through the HTTP-aware APIs of Java, PL/SQL, or Perl. You can display or process the data through any kind of application, including a regular Web browser or an XML-aware application such as a spreadsheet. The servlet supports generating XML and non-XML content and also transforming the results using XSLT stylesheets.

Creating Columns and Storing Data Using UriType

You can create database columns using UriType or its child types, or you can store just the text of each URI or URL and create the object types as needed. When storing a mixture of subtypes in the database, you can define a UriType column that can store various subtypes within the same column.

Because these capabilities use object-oriented programming features such as object types and methods, you can derive your own types that inherit from the Oracle-supplied ones. Deriving new types lets you use specialized techniques for retrieving the data or transforming or filtering it before returning it to the program.

See Also:

Chapter 26, "Oracle XML DB Basic Demo", section "8.0 XML DB Demo: Accessing Content Using DBUriServlet; Transforming Content Using XSL".

UriFactory Package

When storing just the URI text in the database, you can use the UriFactory package to turn each URI into an object of the appropriate subtype. UriFactory package creates an instance of the appropriate type by checking what kind of URI is represented by a given string. For example, any URI that begins with http:// is considered an HTTP URL. When the UriFactory package is passed such a URI string, it returns an instance of a HttpUriType object.

See Also:

"Registering New UriType Subtypes with the UriFactory Package"

Other Sources of Information About URIs and URLs

Before you explore the features in this chapter, you should be familiar with the notation for various kinds of URIs.


URI Concepts

This section introduces you to URI concepts.

What Is a URI?

A URI, or Uniform Resource Identifier, is a generalized kind of URL. Like a URL, it can reference any document, and can reference a specific part of a document. It is more general than a URL because it has a powerful mechanism for specifying the relevant part of the document. A URI consists of two parts:

The fragment appears after the # in the following examples.


Only XDBUriType and HttpUriType support the URI fragment in this release. DBUriType does not support the URI fragment.

How to Create a URL Path from an XML Document View

Figure 12-1 shows a view of the XML data stored in a relational table, EMP, in the database, and the columns of data mapped to elements in the XML document. This mapping is referred to as an XML visualization. The resulting URL path can be derived from the XML document view.

Typical URIs look like the following:

UriType Objects Can Use Different Protocols to Retrieve Data

Oracle9i introduces new datatypes in the database to store and retrieve objects that represent URIs. See "UriTypes Store Uri-References" in the following section. Each datatype uses a different protocol, such as HTTP, to retrieve data.

Oracle9i also introduces new forms of URIs that represent references to rows and columns of database tables.

Advantages of Using DBUri and XDBUri

The following are advantages of using DBUri and XDBUri:

UriTypes Store Uri-References

URIs or Universal Resource Identifiers identify resources such as Web pages anywhere on the Web. Oracle9i provides the following UriTypes for storing and accessing external and internal Uri-references:

These datatypes are object types with member functions that can be used to access objects or pages pointed to by the objects. By using UriType, you can:

These are related by an inheritance hierarchy. UriType is an abstract type and the DBUriType, HttpUriType, and XDBUriType are subtypes of UriType. You can reference data stored in CLOBs or other columns and expose them as URLs to the external world. Oracle9i provides a standard servlet than can be installed and run under the Oracle Servlet engine that interprets these URLs.

Advantages of Using UriTypes

Oracle already provides the PL/SQL package UTL_HTTP and the Java class to fetch URL references. The advantages of defining this new UriType datatype in SQL are:

UriType Functions

The UriType abstract type supports a variety of functions that can be used over any subtype. Table 12-1 lists the UriType member functions.

Table 12-1 UriType Member Functions  
UriType Member Functions Description


Returns the value pointed to by the URL as a character LOB value. The character encoding will be that of the database character set.


Returns the URL stored in the UriType. Do not use the attribute "url" directly. Use this function instead. This can be overridden by subtypes to give you the correct URL. For example, HttpUriType stores only the URL and not the "http://" prefix. Hence getUrl() actually prepends the prefix and returns the value.


Similar to the former (getUrl), except that it calls the escaping mechanism to escape the characters in the URL as to conform to the URL specification. For example spaces are converted to the escaped value %20.

See How Oracle9i Database Works with URLs and URIs .


Returns the MIME information for the URL. For UriType, this is an abstract function.


Returns the XMLType object corresponding to the given URI. This is provided so that an application that needs to perform operations other than getClob/getBlob can use the XMLType methods to do those operations.

This throws an exception if the URI does not point to a valid XML document.


Returns the BLOB value pointed to by the URL. No character conversions are performed and the character encoding is the same as the one pointed to by the URL. This can also be used to fetch binary data.

createUri(uri IN VARCHAR2)

This constructs the UriType. It is not actually in UriType, rather it is used for creating URI subtypes.

HttpUriType Functions

Use HttpUriType to store references to data that can be accessed through the HTTP protocol. HttpUriType uses the UTL_HTTP package to fetch the data and hence the session settings for the package can also be used to influence the HTTP fetch using this mechanism. Table 12-2 lists the HttpUriType member functions.

Table 12-2 HttpUriType Member Functions   (Page 1 of 2)
HttpUriType Method Description


Returns the value pointed to by the URL as a character LOB value. The character encoding is the same as the database character set.


Returns stored URL.


Similar to getUrl, except that it calls the escaping mechanism to escape the characters in the URL as to conform to the URL specification. For example, spaces are converted to the escaped value %20.


Gets the binary content as a BLOB. If the target data is non-binary then the BLOB will contain the XML or text representation of the data in the database character set.


Returns the XMLType object corresponding to this URI. Will throw an error if the target data is not XML. See also "getXML() Function".


Returns the MIME information for the URL. See also "getContentType() Function".


httpUriType constructor. Constructs in httpUriType.


httpUriType constructor. Constructs in httpUriType.

getContentType() Function

getContentType() function returns the MIME information for the URL. The HttpUriType de-references the URL and gets the MIME header information. You can use this information to decide whether to retrieve the URL as BLOB or CLOB based on the MIME type. You would treat a Web page with a MIME type of x/jpeg as a BLOB, and one with a MIME type of text/plain or text/html as a CLOB.

Example 12-1 Using getContentType() and HttpUriType to Return HTTP Headers

Getting the content type does not fetch all the data. The only data transferred is the HTTP headers (for HTTPURiType) or the metadata of the column (for DBUriType). For example:

  httpuri HttpUriType;
  x clob;  
  y blob;
  httpuri := HttpUriType('');
  if httpuri.getContentType() = 'application-x/bin' then
     y := httpuri.getblob();
     x := httpuri.getclob();
  end if;

getXML() Function

getXML() function returns XMLType information for the result. If the document is not valid XML (or XHTML) an error is thrown.

DBUri, Intra-Database References

DBUri, a database relative to URI, is a special case of the Uri-ref mechanism, where ref is guaranteed to work inside the context of a database and session. This ref is not a global ref like the HTTP URL; instead it is local ref (URL) within the database.

You can also access objects pointed to by this URL globally, by appending this DBUri to an HTTP URL path that identifies the servlet that can handle DBUri. This is discussed in "Turning a URL into a Database Query with DBUri Servlet" .

Formulating the DBUri

The URL syntax is obtained by specifying XPath-like syntax over a virtual XML visualization of the database. See Figure 12-1, "DBUri: Visual or SQL View, XML View, and Associated XPath":

Example 12-2 The Virtual XML Document that Scott Sees

For example, the user scott can see the following virtual XML document.

<?xml version='1.0'?>
<oradb SID="ORCL">
      <!-- EMp table -->

Figure 12-1 DBUri: Visual or SQL View, XML View, and Associated XPath

Text description of adxml100.gif follows
Text description of the illustration adxml100.gif

This XML document is constructed at the time you do the query and based on the privileges that you have at that moment.

You can make the following observations from the previous example:

Notation for DBUriType Fragments

With the Oracle9i database being visualized as an XML tree, you can perform XPath traversals to any part of the virtual document. This translates to any row-column intersection of the database tables or views. By specifying an XPath over the visualization model, you can create references to any piece of data in the database.

DbUri is specified in a simplified XPath format. Currently, Oracle does not support the full XPath or XPointer recommendation for DBURType. The following sections discuss the structure of the DBUri.

As stated in the previous paragraphs, you can now create DBUris to any piece of data. You can use the following instances in a column as reference:

These are the smallest addressable units. For example, you can use:





Oracle does not currently support references within a scalar, XMLType or LOB data column.

DBUri Syntax Guidelines

There are restrictions on the kind of XPath queries that can be used to specify a reference. In general, the fragment part must:

Example 12-3 Specifying Predicate pono=100 With the ROW Node

For example, if you wanted to specify the predicate pono = 100, but the selection path is:


you must include the pono predicate along with the ROW node as:


Using Predicate (XPath) Expressions in DBUris

The predicate expressions can use the following XPath expressions:

The predicates can be defined at any element other than the schema and table elements. If you have object columns, you can search on the attribute values as well.

Example 12-4 Searching for Attribute Values on Object Columns Using DBUri

For example, the following DBUri refers to an ADDRESS column containing state, city, street, and zip code attributes:


This DBUri identifies the city attribute whose state is either California or Oregon, or whose city name is Portland, or whose zipcode is 94404.

See Also: for an explanation of the XML XPath notation

Some Common DBUri Scenarios

The DBUri can identify various objects, such as a table, a particular row, a particular column in a row, or a particular attribute of an object column. The following subsections describe how to identify different object types.

Identifying the Whole Table

This returns an XML document that retrieves the whole table. The enclosing tag is the name of the table. The row values are enclosed inside a ROW element, as follows, using the following syntax:


Example 12-5 Using DBUri to Identify a Whole Table as an XML Document

For example:


returns an XML document with a format like the following:

<?xml version="1.0"?>
   ... <!-- other columns -->
 <!-- other rows -->

Identifying a Particular Row of the Table

This identifies a particular ROW element in the table. The result is an XML document that contains the ROW element with its columns as child elements. Use the following syntax:


Example 12-6 Using DBUri to Identify a Particular Row in the Table

For example:


returns the XML document with a format like the following:

<?xml version="1.0"?>
  <!-- other columns -->


In the previous example, the predicate expression must identify a unique row.

Identifying a Target Column

In this case, a target column or an attribute of a column is identified and retrieved as XML.


You cannot traverse into nested table or VARRAY columns.

Use the following syntax:


Example 12-7 Using DBUri to Identify a Specific Column


retrieves the ename column in the emp table, where empno is 7369, and department number is 20, as follows:

<?xml version="1.0"?>

Example 12-8 Using DBUri to Identify an Attribute Inside a Column


retrieves the state attribute inside an address object column for the employee whose empno is 7369, as follows:

<?xml version="1.0"?>

Retrieving the Text Value of a Column

In many cases, it can be useful to retrieve only the text values of a column and not the enclosing tags. For example, if XSL stylesheets are stored in a CLOB column, you can retrieve the document text without having any enclosing column name tags. You can use the text() function for this. It specifies that you only want the text value of the node. Use the following syntax:


Example 12-9 Using DBUri to Retrieve Only the Text Value of the Node

For example:


retrieves the text value of the employee name, without the XML tags, for an employee with empno = 7369. This returns a text document, not an XML document, with value SMITH.


The XPath alone does not constitute a valid URI. Oracle calls it a DBUri since it behaves like a URI within the database, but it can be translated into a globally valid Uri-ref.


The path is case-sensitive. To specify scott.emp, you use SCOTT/EMP, because the actual table and column names are stored capitalized in the Oracle data dictionary. If you need to use lowercase path values, you can create a lowercase table or column name by enclosing the name in double quotation marks.

How DBUris Differ from Object References

A DBUri can access columns and attributes and is loosely typed Object references can only access row objects. DBUri is a superset of this reference mechanism.

DBUri Applies to a Database and Session

A DBUri is scoped to a database and session. You must already be connected to the database in a particular session context. The schema and permissions needed to access the data are resolved in that context.


The same URI string may give different results based on the session context used, particularly if the PUBLIC path is used.

For example, /PUBLIC/FOO_TAB can resolve to SCOTT.FOO_TAB when connected as scott, and resolve as JONES.FOO_TAB when connected as JONES.

Where Can DBUri Be Used?

Uri-ref can be used in a number of scenarios, including those described in the following sections:

Storing URLs to Related Documents

In the case of a travel story Web site where you store travel stories in a table, you might create links to related stories. By representing these links in a DBUriType column, you can create intra-database links that let you retrieve related stories through queries.

Storing Stylesheets in the Database

Applications can use XSL stylesheets to convert XML into other formats. The stylesheets are represented as XML documents, stored as CLOBs. The application can use DBUriType objects:

DBUriType Functions

Table 12-3 lists the DBUriType methods and functions.

Table 12-3
Method/Function Description


Returns the value pointed to by the URL as a character LOB value. The character encoding is the same as the database character set.


Returns the URL that is stored in the DBUriType.


Similar to getUrl, except that it calls the escaping mechanism to escape the characters in the URL as to conform to the URL specification. For example, spaces are converted to the escaped value %20.


Gets the binary content as a BLOB. If the target data is non-binary, then the BLOB will contain the XML or text representation of the data in the database character set.


Returns the XMLType object corresponding to this URI.


Returns the MIME information for the URL.


Constructs a DBUriType instance.


Constructs a DBUriType instance.

DBUriType Methods and Functions

Some of the functions that have a different or special behavior in the DBUriType are described in the following subsections.

getContentType() Function

This function returns the MIME information for the URL. The content type for a DBUriType object can be:

For example, consider the table dbtab under SCOTT:

CREATE TABLE DBTAB( a varchar2(20), b blob);

A DBUriType of '/SCOTT/DBTAB/ROW/A' has a content type of text/xml, since it points to the whole column and the result is XML.

A DBUriType of '/SCOTT/DBTAB/ROW/B' also has a content type of text/xml.

A DBUriType of '/SCOTT/DBTAB/ROW/A/text()' has a content type of text/plain.

A DBUriType of '/SCOTT/DBTAB/ROW/B/text()' has a content type of text/plain.

getClob() and getBlob() Functions

In the case of DBUri, scalar binary data is handled specially. In the case of a getClob() call on a DBUri '/SCOTT/DBTAB/ROW/B/text()' where B is a BLOB column, the data is converted to HEX and sent out.

In the case of a getBlob() call, the data is returned in binary form. However, if an XML document is requested, as in '/SCOTT/DBTAB/ROW/B', then the XML document will contain the binary in HEX form.


XDBUriType is a new subtype of UriType. It provides a way to expose documents in the ORACLE XML DB Repository as URIs that can be embedded in any UriType column in a table.

The URL part of the URI is the hierarchical name of the XML document it refers to. The optional fragment part uses the XPath syntax, and is separated from the URL part by '#'.

The following are examples of ORACLE XML DB URIs:



Table 12-4 lists the XDBUriType methods. These methods do not take any arguments.

Table 12-4 XDBUriType Methods  
Method Description


Returns the value pointed to by the URL as a Character Large Object (CLOB) value. The character encoding is the same as the database character set.

get Blob()

Returns the value pointed to by the URL as a Binary Large Object (BLOB) value.


Returns the URL that is stored in the XDBUriType.


Similar to getUrl, except that it calls the escaping mechanism to escape the characters in the URL as to conform to the URL specification. For example, spaces are converted to the escaped value %20.


Returns the XMLType object corresponding to the contents of the resource that this URI points to. This is provided so that an application that needs to perform operations other than getClob/getBlob can use the XMLType methods to do those operations.


Returns the MIME information for the resource stored in the ORACLE XML DB Repository.


Constructor. Returns an XDBUriType for the given URI.

How to Create an Instance of XDBUriType

XDBUriType is automatically registered with UriFactory so that an XDBUriType instance can be generated by providing the URI to the getURI method.

Currently, XDBUriType is the default UriType generated by the UriFactory.getUri method, when the URI does not have any of the recognized prefixes, such as "http://","/DBURI", or "/ORADB".

All DBUriType URIs should have a prefix of either /DBURI or /ORADB, case insensitive.

Example 12-10 Returning XDBUriType Instance

For example, the following statement returns an XDBUriType instance that refers to /home/scott/doc1.xml:

SELECT sys.UriFactory.getUri('/home/scott/doc1.xml') FROM dual;

Example 12-11 Creating XDBUriType, Inserting Values Into a Purchase Order Table and Selecting All the PurchaseOrders

The following is an example of how XDBUriType is used:

  poUrl SYS.UriType,  -- Note that we have created an abstract type column
                       --so that any type of URI can be used
   poName VARCHAR2(1000)
 -- insert an absolute url into poUrl
 -- the factory will create an XDBUriType since there's no prefix
  (UriFactory.getUri('/public/orders/po1.xml'), 'SomePurchaseOrder');
-- Now get all the purchase orders
SELECT e.poUrl.getClob(), poName FROM uri_tab e;

-- Using PL/SQL, you can access table uri_tab as follows: 
   a UriType;
  -- Get the absolute URL for purchase order named like 'Some%'
   SELECT poUrl into a from uri_tab WHERE poName like 'Some%';

Example 12-12 Retrieving Purchase Orders at a URL Using UriType, getXML() and extractValue()

Since getXML() returns an XMLType, it can be used in the EXTRACT family of operators. For example:

SELECT e.poUrl.getClob() FROM uri_tab e
   WHERE extractValue(e.poUrl.getXML(),'/User') = 'SCOTT';

This statement retrieves all Purchase Orders for user SCOTT.

Creating Oracle Text Indexes on UriType Columns

UriType columns can be indexed natively in Oracle9i database using Oracle Text. No special datastore is needed.


Chapter 7, "Searching XML Data with Oracle Text","XMLType Indexing"

Using UriType Objects

This section describes how to store pointers to documents and retrieve these documents across the network, either from the database or a Web site.

Storing Pointers to Documents with UriType

As explained earlier, UriType is an abstract type containing a VARCHAR2 attribute that specifies the URI. The object type has functions for traversing the reference and extracting the data.

You can create columns using UriType to store these pointers in the database. Typically, you declare the column using the UriType, and the objects that you store use one or more of the derived types such as HttpUriType.

Table 12-4 lists some useful UriType methods.


You can plug in any new protocol using the inheritance mechanism. Oracle provides HttpUriType and DBUriType types for handling HTTP protocol and for deciphering DBUri references. For example, you can implement a subtype of UriType to handle the gopher protocol.

Example 12-13 Creating URL References to a List of Purchase Orders

You can create a list of all purchase orders with URL references to them as follows:

   poUrl SYS.UriType,  -- Note that we have created abstract type columns
-- if you know what kind of uri's you are going to store, you can 
-- create the appropriate types.
   poName VARCHAR2(200)

 -- insert an absolute url into SYS.UriType..!
 -- the Urifactory creates the correct instance (in this case a HttpUriType

-- insert a URL by directly calling the SYS.HttpUriType constructor. 
-- Note this is strongly discouraged. Note the absence of the
-- http:// prefix when creating SYS.HttpUriType instance through the default
-- constructor. 
INSERT INTO uri_tab VALUES (sys.HttpUriType(''),'RelPo');

-- Now extract all the purchase orders
SELECT e.poUrl.getClob(), poName FROM uri_tab e;

-- In PL/SQL
   a SYS.UriType;

 -- absolute URL
 SELECT poUrl into a from uri_Tab WHERE poName like 'AbsPo%';

 SELECT poUrl into a from uri_Tab WHERE poName like 'RelPo%';
 -- here u need to supply a prefix before u can get at the data..!


"Creating Instances of UriType Objects with the UriFactory Package" for a description of how to use UriFactory

Using the Substitution Mechanism

You can create columns of the UriType directly and insert HttpUriTypes, XDBUriTypes, and DBUriTypes into that column. You can also query the column without knowing where the referenced document lies. For example, from the previous example, you inserted DBUri references into the uri_tab table as follows:


This insert assumes that there is a purchase order table in the SCOTT schema. Now, the URL column in the table contains values that are pointing through HTTP to documents globally as well as pointing to virtual documents inside the database.

A SELECT on the column using the getClob() method would retrieve the results as a CLOB irrespective of where the document resides. This would retrieve values from the global HTTP address stored in the first row as well as the local DBUri reference.:

SELECT e.poURL.getclob() FROM uri_tab e;

Using HttpUriType and DBUriType

HttpUriType and DBUriType are subtypes of UriType and implement the functions for HTTP and DBUri references respectively.


HttpUriType cannot store relative HTTP references in this release.

Example 12-14 DBUriType: Creating DBUri References

The following example creates a table with a column of type DBUriType and assigns a value to it.

CREATE TABLE DBURiTab(DBUri DBUriType, dbDocName VARCHAR2(2000));

-- insert values into it..!


-- access the references
SELECT e.DBUri.getCLOB() from DBUriTab e;

Creating Instances of UriType Objects with the UriFactory Package

The functions in the UriFactory package generate instances of the appropriate UriType subtype (HttpUriType, DBUriType, and XDBUriType). This way, you can avoid hardcoding the implementation in the program and handle whatever kinds of URI strings are used as input. See Table 12-5.

The getUri method takes a string representing any of the supported kinds of URI and returns the appropriate subtype instance. For example:

Registering New UriType Subtypes with the UriFactory Package

The UriFactory package lets you register new UriType subtypes:

For example, you can invent a new protocol ecom:// and define a subtype of UriType to handle that protocol. Perhaps the subtype implements some special logic for getCLOB, or does some changes to the XML tags or data within getXML. When you register the ecom:// prefix with UriFactory, any calls to UriFactory.getUri generate the new subtype instance for URIs that begin with the ecom:// prefix.

Table 12-5 UriFactory: Functions and Procedures
UriFactory Function Description


MEMBER FUNCTION escapeUri() RETURN varchar2

Escapes the URL string by replacing the non-URL characters as specified in the Uri-ref specification by their equivalent escape sequence.


FUNCTION unescapeUri() RETURN varchar2

Unescapes a given URL.


PROCEDURE registerUrlHandler(prefix IN varchar2, schemaName in varchar2, typename in varchar2, ignoreCase in boolean:= true, stripprefix in boolean := true)

Registers a particular type name for handling a particular URL.

The type also implements the following static member function: STATIC FUNCTION createUri(url IN varchar2) RETURN <typename>;

This function is called by getUrl() to generate an instance of the type. The stripprefix indicates that the prefix must be stripped off before calling the appropriate constructor for the type.


PROCEDURE unregisterUrlHandler(prefix in varchar2)

Unregisters a URL handler.

Example 12-15 UriFactory: Registering the ecom Protocol

Assume you are storing different kinds of URIs in a single table:

CREATE TABLE url_tab (urlcol varchar2(80));

-- Insert an HTTP URL
INSERT INTO url_tab VALUES ('');

-- Insert a database URI

-- Create a new type to handle a new protocol called ecom://
  overriding member function getClob return clob,
  overriding member function getBlob RETURN blob,
  overriding member function getExternalUrl return varchar2,
  overriding member function getUrl return varchar2,

-- Must have this for registering with the URL handler
static function createUri(url in varchar2) return EcomUriType

-- Register a new handler for the ecom:// prefix.
  -- register a new handler for ecom:// prefixes. The handler
  -- type name is ECOMUriTYPE, schema is SCOTT
  -- Ignore the prefix case, so that UriFactory creates the same subtype
  -- for URIs beginning with ECOM://, ecom://, eCom://, and so on.
  -- Strip the prefix before calling the createUri function
  -- so that the string 'ecom://' is not stored inside the
  -- ECOMUriTYPE object. (It is added back automatically when
  -- you call ECOMUriTYPE.getURL.)
    prefix => 'ecom://',
    schemaname => 'SCOTT',
    typename => 'ECOMURITYPE',
    ignoreprefixcase => true,
    stripprefix => true

-- Now the example inserts this new type of URI into the table.
insert into url_tab values ('ECOM://company1/company2=22/comp');

-- Use the factory to generate an instance of the appropriate
-- subtype for each URI in the table.
select urifactory.getUri(urlcol) from url_tab;

-- would now generate
HttpUriType(''); -- a Http uri type instance

DBUriType('/oradb/SCOTT/EMPLOYEE/ROW[ENAME="Jack"],null); -- a DBUriType

EComUriType('company1/company2=22/comp'); -- an EComUriType instance

Why Define New Subtypes of UriType?

Deriving a new class for each protocol has these advantages:


You can create an instance of DBUriType type by specifying the path expression to the constructor or the UriFactory methods. However, you also need methods to generate these objects dynamically, based on strings stored in table columns. You do this with the SQL function SYS_DBURIGEN().

Example 12-16 SYS_DBURIGEN(): Generating a URI of type DBUriType that points to a Column

The following example uses SYS_DBURIGEN() to generate a URI of datatype DBUriType pointing to the email column of the row in the sample table hr.employees where the employee_id = 206:

SELECT SYS_DBURIGEN(employee_id, email)
   FROM employees
   WHERE employee_id = 206;


SYS_DBURIGEN() takes as its argument one or more columns or attributes, and optionally a rowid, and generates a URI of datatype DBUriType to a particular column or row object. You can use the URI to retrieve an XML document from the database. The function takes an additional parameter to indicate if the text value of the node is needed. See Figure 12-2.

Figure 12-2 SYS_DBURIGEN Syntax

Text description of sys_dburigen.gif follows
Text description of the illustration sys_dburigen.gif

All columns or attributes referenced must reside in the same table. They must reference a unique value. If you specify multiple columns, the initial columns identify the row in the database, and the last column identifies the column within the row.

By default, the URI points to a formatted XML document. To point only to the text of the document, specify the optional text() keyword.

See Also:

Oracle9i SQL Reference for SYS_DBURIGEN syntax

If you do not specify an XML schema, Oracle interprets the table or view name as a public synonym.

Rules for Passing Columns or Object Attributes to SYS_DBURIGEN()

The column or attribute passed to the SYS_DBURIGEN() function must obey the following rules:

Example 12-17 Passing Columns With Single Arguments to SYS_DBURIGEN()

For example:

select SYS_DBURIGEN(empno) from emp
   WHERE empno=7369;

uses the empno both as the key column and the referenced column, generating a URL of the form:


for the row with empno=7369


Example 12-18 Inserting Database References Using SYS_DBURIGEN()

CREATE TABLE doc_list_tab(docno number primary key, doc_ref SYS.DBUriType);

-- inserts /SCOTT/EMP/ROW[rowid='xxx']/EMPNO
INSERT INTO doc_list_tab values(1001, 
     (select SYS_DBURIGEN(rowid,empno) from emp where empno = 100));

-- insert a Uri-ref to point to the ename column of emp!
INSERT INTO doc_list_tab values(1002,
   (select SYS_DBURIGEN(empno, ename) from emp where empno = 7369));

-- result of the DBURIGEN looks like, /SCOTT/EMP/ROW[EMPNO=7369]/ENAME

Returning Partial Results

When selecting the results of a large column, you might want to retrieve only a portion of the result and create a URL to the column instead. For example, consider the case of a travel story Web site. If all the travel stories are stored in a table, and users search for a set of relevant stories, you do not want to list each entire story in the result page. Instead, you show the first 100 characters or gist of the story and then return a URL to the full story.This can be done as follows:

Example 12-19 Returning a Portion of the Results By Creating a View and Using SYS_DBURIGEN()

Assume that the travel story table is defined as follows:

CREATE TABLE travel_story 
  story_name varchar2(100),
  story clob

-- insert some value..!
INSERT INTO travel_story values ('Egypt','This is my story of how I spent my 
time in Egypt, with the pyramids in full view from my hotel room');

Now, you create a function that returns only the first 20 characters from the story:

create function charfunc(clobval IN clob ) return varchar2 is
 res varchar2(20);
 amount number := 20;
  return res;

Now, you create a view that selects out only the first 100 characters from the story and then returns a DBUri reference to the story column:

CREATE VIEW travel_view as select story_name, charfunc(story) short_story,
   SYS_DBURIGEN(story_name,story,'text()') story_link
FROM travel_story;

Now, a SELECT from the view returns the following:

SELECT * FROM travel_view;
Egypt           This is my story of h   



You can use SYS_DBURIGEN() in the RETURNING clause of DML statements to retrieve the URL of an object as it is inserted.

Example 12-20 Using SYS_DBURIGEN in the RETURNING Clause to Retrieve the URL of an Object

For example, consider the table CLOB_TAB:

CREATE TABLE clob_tab ( docid number, doc clob);

When you insert a document, you might want to store the URL of that document in another table, URI_TAB.

CREATE TABLE uri_tab (docs sys.DBUriType);

You can specify the storage of the URL of that document as part of the insert into CLOB_TAB, using the RETURNING clause and the EXECUTE IMMEDIATE syntax to execute the SYS_DBURIGEN function inside PL/SQL as follows:

  ret sys.dburitype;
  -- exucute the insert and get the url
'insert into clob_tab values (1,''TEMP CLOB TEST'') 
 RETURNING SYS_DBURIGEN(docid, doc, ''text()'') INTO :1 '
 -- insert the url into uri_tab
insert into uri_tab values (ret);

The URL created has the form:



The text() keyword is appended to the end indicating that you want the URL to return just the CLOB value and not an XML document enclosing the CLOB text.

Turning a URL into a Database Query with DBUri Servlet

You can make table data accessible from your browser or any Web client, using the URI notation within a URL to specify the data to retrieve:

DBUri Servlet Mechanism

For the preceding methods, a servlet runs for accessing this information through HTTP. This servlet takes in a path expression following the servlet name as the DBUri reference and outputs the document pointed to by the DBUri to the output stream.

The generated document can be a Web page, an XML document, plain text, and so on. You can specify the MIME type so that the browser or other application knows what kind of content to expect:

Example 12-21 URL for Overriding the MIME Type by Generating the contenttype Argument, to Retrieve the empno Column of Table Employee

For example, to retrieve the empno column of the employee table, you can write a URL such as one of the following:

-- Generates a contenttype of text/plain[EMPNO=7369]/ENAME/text()
-- Generates a contenttype of text/xml[EMPNO=7369/ENAME

where the machine is running the Oracle9i database, with a Web service at port 8080 listening to requests. oradb is the virtual path that maps to the servlet.

DBUri Servlet: Optional Arguments

Table 12-6 describes the three optional arguments you can pass to DBUri servlet to customize the output.

Table 12-6 DBUri Servlet: Optional Arguments  
Argument Description


Changes the default root tag name for the XML document. For example:


Specifies the MIME type of the returned document. For example:


This argument passes a URL to UriFactory, which in turn retrieves the XSL stylehseet at that location. This stylesheet is then applied to the XML document being returned by the servlet. For example:


When using XPath notation in the URL for this servlet, you may have to escape certain characters such as square brackets. You can use the getExternalUrl() functions in the UriType types to get an escaped version of the URL.


In HTTP access, special characters such as, ], [, &, | have to be escaped using the %xx format, where xx is the hexadecimal number of the ASCII code for that character. Use the getExternalUrl() function in the UriType family to get an escaped version of the URL.

Installing DBUri Servlet

DbUriServlet is built into the database, and the installation is handled by the ORACLE XML DB configuration file. To customize the installation of the servlet, you need to edit it. You can edit the config file, xdbconfig.xml under the ORACLE XML DB user, through WebDAV, FTP, from Oracle Enterprise Manager, or in the database. To update the file using FTP or WebDAV, simply download the document, edit it as necessary, and save it back in the database. There are several things that can be customized using the configuration file.

See Also:

Notice that the servlet is installed at /oradb/* specified in the servlet-pattern tag. The * is necessary to indicate that any path following oradb is to be mapped to the same servlet. The oradb is published as the virtual path. Here, you can change the path that will be used to access the servlet.

Example 12-22 Installing DBUri Servlet Under /dburi/*

For example, to have the servlet installed under /dburi/*, you can run the following PL/SQL:

    doc XMLType;
  doc2 XMLType;
  doc := dbms_xdb.cfg_get();
  select updateXML(doc,   
, '/dburi/*') into doc2 from dual;

Security parameters, the servlet display-name, and the description can also be customized in the xdbconfig.xml configuration file. See Appendix A, "Installing and Configuring Oracle XML DB" and Chapter 20, "Writing Oracle XML DB Applications in Java". The servlet can be removed by deleting the servlet-pattern for this servlet. This can also be done using updateXML() to update the servlet-mapping element to null.

DBUri Security

Servlet security is handled by Oracle9i database using roles. When users log in to the servlet, they use their database username and password. The servlet will check to make sure the user logging in belongs to one of the roles specified in the configuration file. The roles allowed to access the servlet are specified in the security-role-ref tag. By default, the servlet is available to the special role authenticatedUser. Any user who logs into the servlet with any valid database username and password belongs to this role.

This parameter can be changed to restrict access to any role(s) in the database. To change from the default authenticated-user role to a role that you have created, say servlet-users, run:

    doc XMLType;
  doc2 XMLType;
    doc3 XMLType;
  doc := dbms_xdb.cfg_get();
  select updateXML(doc, 
, 'servlet-users') into doc2 from dual;
  select updateXML(doc2, 
, 'servlet-users') into doc3 from dual;


Configuring the UriFactory Package to Handle DBUris

The UriFactory, as explained in "Creating Instances of UriType Objects with the UriFactory Package", takes a URL and generates the appropriate subtypes of the UriType to handle the corresponding protocol. For HTTP URLs, UriFactory creates instances of the HttpUriType. But when you have an HTTP URL that represents a URI path, it is more efficient to store and process it as a DBUriType instance in the database. The DBUriType processing involves fewer layers of communication and potentially fewer character conversions.

After you install OraDBUriServlet, so that any URL such as http://machine-name/servlets/oradb/ gets handled by that servlet, you can configure the UriFactory to use that prefix and create instances of the DBUriType instead of HttpUriType:

 -- register a new handler for the dburi prefix..     
        ,'SYS','DBUriTYPE', true,true);

After you execute this block in your session, any UriFactory.getUri() call in that session automatically creates an instance of the DBUriType for those HTTP URLs that have the prefix.

See Also:

Oracle9i XML API Reference - XDK and Oracle XML DB for details of all functions in DBUriFactory package.