This chapter describes how to generate and store URLs in the database and how to retrieve data pointed to by those URLs. Three kinds of URIs are discussed:
DBUris – addresses to relational data in the database
XDBUris – addresses to data in Oracle XML DB Repository
HTTPUris – Web addresses that use the Hyper Text Transfer Protocol (HTTP(S))
This chapter contains these topics:
The two main features described in this chapter are these:
Using paths as an indirection mechanism – You can store a path in the database and then access its target indirectly by referring to the path. The paths in question are various kinds of Uniform Resource Identifier (URI).
Using paths that target database data to produce XML documents – One kind of URI that you can use for indirection in particular, a DBUri, provides a convenient XPath notation for addressing database data. You can use a DBUri to construct an XML document that contains database data and whose structure reflects the database structure.
In developing Web-based XML applications, you often refer to data located on a network using Uniform Resource Identifiers, or URIs. A URL, or Uniform Resource Locator, is a URI that accesses an object using an Internet protocol.
A URI has two parts, separated by a number sign (
A URL part, that identifies a document.
A fragment part, that identifies a fragment within the document. The notation for the fragment depends on the document type. For HTML documents, it is an anchor name. For XML documents, it is an XPath expression.
These are typical URIs:
For HTML –
some_anchor is a named anchor in the HTML document.
For XML –
http://www.xml.com/xml_doc identifies the location of the XML document.
/po/cust/custname identifies a fragment within the document. This portion is defined by the W3C XPointer recommendation.
http://www.w3.org/2002/ws/Activity.html an explanation of HTTP(S) URL notation
http://www.w3.org/TR/xpath for an explanation of the XML XPath notation
http://www.w3.org/TR/xptr/ for an explanation of the XML XPointer notation
http://xml.coverpages.org/xmlMediaMIME.html for a discussion of MIME types
Oracle XML DB can represent paths of various kinds as database objects. These are the available path object types:
HTTPURIType – An object of this type is called an HTTPUri and represents a URL that begins with
HTTPURIType, you can create objects that represent links to remote Web pages (or files) and retrieve those Web pages by calling object methods. This type implements the Hyper Text Transfer Protocol (HTTP(S)) for accessing remote Web pages.
HTTPURIType uses package
UTL_HTTP to fetch data, so session settings for this package can also be used to influence HTTP fetches.
See Also :"HTTPURIType Method getContentType()"
DBURIType – An object of this type is called a DBUri and represents a URI that targets database data – a table, one or more rows, or a single column. With
DBURIType, you can create objects that represent links to database data, and retrieve such data as XML by calling object methods. A DBUri uses a simple form of XPath expression as its URI syntax – for example, the following XPath expression is a DBUri reference to the row of database table
employees where column
first_name has value
See Also :DBUris: Pointers to Database Data
XDBURIType – An object of this type is called an XDBUri and represents a URI that targets a resource in Oracle XML DB Repository. With
XDBURIType, you can create objects that represent links to repository resources, and retrieve all or part of any resource by calling object methods. The URI syntax for an XDBUri is a repository resource address optionally followed by an XPath expression. For example,
/public/hr/doc1.xml#/purchaseOrder/lineItem is an XDBUri reference to the
lineItem child element of the root element
purchaseOrder in repository file
doc1.xml in folder
See Also :XDBUris: Pointers to Repository Resources
Each of these object types is derived from an abstract object type,
URIType. As an abstract type, it has no instances (objects); only its subtypes have instances.
URIType provides the following features:
Unified access to data stored inside and outside the server. Because you can use
URIType values to store pointers to HTTP(S) and DBUris, you can create queries and indexes without worrying about where the data resides.
Mapping of URIs in XML Documents to Database Columns. When an XML document is shredded to database tables and columns, any URIs contained in the document are mapped to database columns of the appropriate
You can reference data stored in relational columns and expose it to the external world using URIs. Oracle Database provides a standard servlet, DBUriServlet, that interprets DBUris. It also provides PL/SQL package
UTL_HTTP and Java class
java.net.URL, which you can use to fetch URL references.
URIType columns can be indexed natively in Oracle Database using Oracle Text – no special datastore is needed.
"Creating New Subtypes of URIType using Package URIFACTORY" for information on defining new
The following are typical uses of DBUris and XDBUris:
You can reference XSLT style sheets from within database-generated Web pages. Package
DBMS_METADATA uses DBUris to reference XSL style sheets. An XDBUri can be used to reference XSLT style sheets stored in Oracle XML DB Repository.
You can reference HTML text, images and other data stored in the database. URLs can be used to point to data stored in database tables or in repository folders.
You can improve performance by bypassing the Web server. Replace a global URL in your XML document with a reference to the database, and use a servlet, a DBUri, or a XDBUri to retrieve the targeted content. Using a DBUri or an XDBUri generally provides better performance than using a servlet, because you interact directly with the database rather than through a Web server.
With a DBUri, you can access an XML document in the database without using SQL.
Whenever a repository resource is stored in a database table to which you have access, you can use either an XDBUri or a DBUri to access its content.
See Also:Oracle Database PL/SQL Packages and Types Reference, "DBMS_METADATA package"
Abstract object type
URIType includes methods that can be used with each of its subtypes. Each of these methods can be overridden by any of the subtypes. Table 19-1 lists the
URIType methods. In addition, each of the subtypes has a constructor with the same name as the subtype.
Returns the URL of the
Use this method instead of referencing a URL directly.
Returns the MIME content type for the URI.
HTTPUri: The URL is followed and the MIME header examined, in order to return the actual content type.
DBUri: The returned content type is either
XDBUri: The value of the
Returns the target of the URI as a
DBUri: XML data is returned (unless node-test
Returns the target of the URI as a
DBUri: When applied to a DBUri that targets a
Returns the target of the URI as an
Constructs an instance of one of the
getContentType() returns the actual MIME information for its targeted document. You can use this information to decide whether to retrieve the document as a
BLOB value or a
CLOB value. For example, you might treat a Web page with a MIME type of
x/jpeg as a
BLOB value, and one with a MIME type of
text/html as a
In this example, the HTTP content type is tested to determine whether to retrieve data as a
BLOB value. The content-type data is the HTTP header, for
HTTPURIType, or the metadata of the database column, for
DECLARE httpuri HTTPURIType; y CLOB; x BLOB; BEGIN httpuri := HTTPURIType('http://www.oracle.com/object1'); DBMS_OUTPUT.put_line(httpuri.getContentType()); IF httpuri.getContentType() = 'text/html' THEN y := httpuri.getClob(); END IF; IF httpuri.getContentType() = 'application-x/bin' THEN x := httpuri.getBlob(); END IF; END; / text/html
getContentType() returns the MIME information for a URL. If a DBUri targets a scalar value, then the MIME content type returned is
text/plain; otherwise, it is
text/xml. For example, consider table
CREATE TABLE DBTAB(a VARCHAR2(20), b BLOB);
DBUris corresponding to the following XPath expressions have content type
text/xml, because each targets a complete column of XML data.
DBUris corresponding to the following XPath expressions have content type
text/plain, because each targets a scalar value.
getClob() is applied to a DBUri, the targeted data is returned as XML data, using the targeted column or table name as an XML element name. If the target XPath uses node-test
text(), then the data is returned as text without an enclosing XML tag. In both cases, the returned data is in the database character set.
For example: If appliedto a DBUri with XPath
A is a non-binary column, the data in column
A is returned as is. Without XPath node-test
text(), the result is the data wrapped in XML:
When applied toa DBUri that targets a binary (
BLOB) column, the binary data in the column is translated as hexadecimal character data.
For example: If applied to a DBUri with XPath
B is a
BLOB column, the targeted binary data is translated to hexadecimal character data and returned. Without XPath node-test
text(), the result is the translated data wrapped in XML:
When applied to a DBUri that targets a
getBlob() returns the binary data translated as hexadecimal character data. When applied to a DBUri that targets non-binary data,
getBlob() returns the data (as a
BLOB value) in the database character set.
For example, consider table
CREATE TABLE DBTAB(a VARCHAR2(20), b BLOB);
getBlob() is applied to a DBUri corresponding to XPath expression
/HR/DBTAB/ROW/B, it returns a
BLOB value containing an XML document with root element
B whose content is the hexadecimal-character translation of the binary data of column
getBlob() is applied to a DBUri corresponding to XPath expression
/HR/DBTAB/ROW/B/text(), it returns a
BLOB value containing only the hexadecimal-character translation of the binary data of column
getBlob() is applied to a DBUri corresponding to XPath expression
/text(), which targets non-binary data, it returns a
BLOB value containing the data of column
A, in the database character set.
To use instances of
URIType subtypes for indirection, you generally store such instances in the database and then use them in queries with a method such as
getClob() to retrieve the targeted data. This section illustrates how to do this.
You can create database columns using
URIType or any of its subtypes, or you can store just the text of each URI as a string and then create the needed
URIType instances on demand, when the URIs are accessed. You can store objects of different
URIType subtypes in the same
URIType database column.
You can also define your own object types that inherit from the
URIType subtypes. Deriving new types lets you use custom techniques to retrieve, transform, or filter data.
"Creating New Subtypes of URIType using Package URIFACTORY" for information on defining new
"XSL Transformation and Oracle XML DB" for information on transforming XML data
This example stores an HTTPUri and a DBUri (instances of
DBURIType) in the same database column of type
URIType. A query retrieves the data addressed by each of the URIs. The first URI is a Web-page URL; the second references data in the
employees table of standard schema
hr. (For brevity, only the beginning of the Web page is shown.)
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (HTTPURIType.createURI('http://www.oracle.com')); 1 row created. INSERT INTO uri_tab VALUES (DBURIType.createURI( '/HR/EMPLOYEES/ROW[FIRST_NAME="Jack"]')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() ------------------------------------------------------------------- <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML> <HEAD> <TITLE>Oracle Corporation</TITLE> . . . <?xml version="1.0"?> <ROW> <EMPLOYEE_ID>177</EMPLOYEE_ID> <FIRST_NAME>Jack</FIRST_NAME> <LAST_NAME>Livingston</LAST_NAME> <EMAIL>JLIVINGS</EMAIL> <PHONE_NUMBER>011.44.1644.429264</PHONE_NUMBER> <HIRE_DATE>23-APR-98</HIRE_DATE> <JOB_ID>SA_REP</JOB_ID> <SALARY>8400</SALARY> <COMMISSION_PCT>.2</COMMISSION_PCT> <MANAGER_ID>149</MANAGER_ID> <DEPARTMENT_ID>80</DEPARTMENT_ID> </ROW> 2 rows selected.
In order to use
createURI(), you must know the particular
URIType subtype to use. Method
getURI() of package
URIFACTORY lets you instead use the flexibility of late binding, determining the particular type information at runtime.
URIFACTORY.getURI() takes as argument a URI string; it returns a
URIType instance of the appropriate subtype (
HTTPURIType, DBURIType, or
XDBURIType), based on the form of the URI string:
If the URI starts with
getURI() creates and returns an HTTPUri.
If the URI starts with either
getURI() creates and returns a DBUri.
getURI() creates and returns an XDBUri.
This example is similar to Example 19-2. However, it uses two different ways to obtain documents targeted by URIs:
SYS.URIFACTORY.getURI() with absolute URIs:
an HTTPUri that targets HTTP address
a DBUri that targets database address
SYS.HTTPURIType() with a relative URL (no
http://). The same HTTPUri is used as for the absolute URI: the Oracle home page.
In this example, the URI strings passed to
getURI() are hard-coded, but they could just as easily be string values that are obtained by an application at runtime.
CREATE TABLE uri_tab (docUrl SYS.URIType, docName VARCHAR2(200)); Table created. -- Insert an HTTPUri with absolute URL into SYS.URIType using URIFACTORY. -- The target is Oracle home page. INSERT INTO uri_tab VALUES (SYS.URIFACTORY.getURI('http://www.oracle.com'), 'AbsURL'); 1 row created. -- Insert an HTTPUri with relative URL using constructor SYS.HTTPURIType. -- Note the absence of prefix http://. The target is the same. INSERT INTO uri_tab VALUES (SYS.HTTPURIType('www.oracle.com'), 'RelURL'); 1 row created. -- Insert a DBUri that targets employee data from database table hr.employees. INSERT INTO uri_tab VALUES (SYS.URIFACTORY.getURI('/oradb/HR/EMPLOYEES/ROW[EMPLOYEE_ID=200]'), 'Emp200'); 1 row created. -- Extract all of the documents. SELECT e.docUrl.getClob(), docName FROM uri_tab e; E.DOCURL.GETCLOB() ----------------- DOCNAME ------------------------------------ <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML> <HEAD> <TITLE>Oracle Corporation</TITLE> . . . AbsURL <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML> <HEAD> <TITLE>Oracle Corporation</TITLE> . . . RelURL <?xml version="1.0"?> <ROW> <EMPLOYEE_ID>200</EMPLOYEE_ID> <FIRST_NAME>Jennifer</FIRST_NAME> <LAST_NAME>Whalen</LAST_NAME> <EMAIL>JWHALEN</EMAIL> <PHONE_NUMBER>515.123.4444</PHONE_NUMBER> <HIRE_DATE>17-SEP-87</HIRE_DATE> <JOB_ID>AD_ASST</JOB_ID> <SALARY>4400</SALARY> <MANAGER_ID>101</MANAGER_ID> <DEPARTMENT_ID>10</DEPARTMENT_ID> </ROW> Emp200 3 rows selected. -- In PL/SQL CREATE OR REPLACE FUNCTION returnclob RETURN CLOB IS a SYS.URIType; BEGIN SELECT docUrl INTO a FROM uri_Tab WHERE docName LIKE 'Emp200%'; RETURN a.getClob; END; / Function created. SELECT returnclob() FROM DUAL; RETURNCLOB() --------------------------------------------------------------- <?xml version="1.0"?> <ROW> <EMPLOYEE_ID>200</EMPLOYEE_ID> <FIRST_NAME>Jennifer</FIRST_NAME> <LAST_NAME>Whalen</LAST_NAME> <EMAIL>JWHALEN</EMAIL> <PHONE_NUMBER>515.123.4444</PHONE_NUMBER> <HIRE_DATE>17-SEP-87</HIRE_DATE> <JOB_ID>AD_ASST</JOB_ID> <SALARY>4400</SALARY> <MANAGER_ID>101</MANAGER_ID> <DEPARTMENT_ID>10</DEPARTMENT_ID> </ROW> 1 row selected.
The URL portion of an XDBUri URI is the hierarchical address of the targeted repository resource – it is a repository path (not an XPath expression).
The optional fragment portion of the URI uses the XPath syntax, and is separated from the URL part by a number-sign (
#). It is appropriate only if the targeted resource is an XML document, in which case the fragment portion targets one or more parts of the XML document. If the targeted resource is not an XML document, then omit the fragment and number-sign.
The following are examples of XDBUri URIs:
Based on the form of these URIs, we can determine the following:
/public/hr is a folder resource in Oracle XML DB Repository.
doc1.xml are resources in folder
doc1.xml is a file resource, and it contains an XML document.
The XPath expression /
PurchaseOrder/LineItem refers to the
LineItem child element in element
PurchaseOrder of XML document
You can create an XDBUri using method
getURI() of package
XDBURIType is the default
URIType used when generating instances using
getURI(), unless the URI has one of the recognized prefixes
For example, if resource
doc1.xml is present in repository folder
/public/hr, then the following query will return an XDBUri that targets that resource.
SELECT SYS.URIFACTORY.getURI('/public/hr/doc1.xml') FROM DUAL;
It is the lack of a special prefix that determines that the type is
XDBURIType, not any particular resource file extension or the presence of
# followed by an XPath expression; if the resource were named
foo.bar instead of
doc1.xml, the returned
URIType instance would still be an XDBUri.
This example creates an XDBUri, inserts values into a purchase-order table, and then selects all of the purchase orders. Because there is no special prefix used in the URI passed to
URIFACTORY.getURI(), the created
URIType instance is an XDBUri.
DECLARE res BOOLEAN; postring VARCHAR2(100):= '<?xml version="1.0"?> <ROW> <PO>999</PO> </ROW>'; BEGIN res:=DBMS_XDB.createFolder('/public/orders/'); res:=DBMS_XDB.createResource('/public/orders/po1.xml', postring); END; / PL/SQL procedure successfully completed. CREATE TABLE uri_tab (poUrl SYS.URIType, poName VARCHAR2(1000)); Table created. -- We create an abstract type column so any type of URI can be used -- Insert an absolute URL into poUrl. -- The factory will create an XDBURIType because there is no prefix. -- Here, po1.xml is an XML file that is stored in /public/orders/ -- of the XML repository. INSERT INTO uri_tab VALUES (URIFACTORY.getURI('/public/orders/po1.xml'), 'SomePurchaseOrder'); 1 row created. -- Get all the purchase orders SELECT e.poUrl.getClob(), poName FROM uri_tab e; E.POURL.GETCLOB() ----------------- PONAME ------ <?xml version="1.0"?> <ROW> <PO>999</PO> </ROW> SomePurchaseOrder 1 row selected. -- Using PL/SQL, you can access table uri_tab as follows: CREATE OR REPLACE FUNCTION returnclob RETURN CLOB IS a URIType; BEGIN -- Get absolute URL for purchase order named like 'Some%' SELECT poUrl INTO a FROM uri_tab WHERE poName LIKE 'Some%'; RETURN a.getClob(); END; / Function created. SELECT returnclob() FROM DUAL; RETURNCLOB() --------------------- <?xml version="1.0"?> <ROW> <PO>999</PO> </ROW> 1 row selected.
getXML() returns an
XMLType instance, you can use it with SQL functions like
extractValue. This query retrieves all purchase orders numbered 999:
SELECT e.poUrl.getClob() FROM uri_tab e WHERE extractValue(e.poUrl.getXML(), '/ROW/PO') = '999'; E.POURL.GETCLOB() --------------------- <?xml version="1.0"?> <ROW> <PO>999</PO> </ROW> 1 row selected.
A DBUri is a URI that targets database data. As for all instances of
URIType subtypes, a DBUri provides an indirection mechanism for accessing data. In addition,
DBURIType lets you do the following:
Address database data using XPath notation. This, in effect, lets you visualize and access the database as if it were XML data.
For example, a DBUri can use an expression such as
/HR/EMPLOYEES/ROW[FIRST_NAME="Jack"] to target the row of database table
employees where column
first_name has value
Construct an XML document that contains database data targeted by a DBUri and whose structure reflects the database structure.
For example: A DBUri with XPath
/HR/DBTAB/ROW/A can be used to construct an XML document that wraps the data of column
A in XML elements that reflect the database structure and are named accordingly:
A DBUri does not reference a global location as does an HTTPUri. You can, however, also access objects addressed by a DBUri in a global manner, by appending the DBUri to an HTTPUri that identifies a servlet that handles DBUris – see "DBUriServlet" .
You can only access those database schemas to which you have been granted access privileges. This portion of the database is, in effect, your own view of the database.
DBURIType, you can have corresponding XML views of the database, which are portions of the database to which you have access, presented in the form of XML data. This means all kinds database data, not just data that is stored as XML. When visualized this way, the database data is effectively wrapped in XML elements, resulting in one or more XML documents.
Such "XML views" are not database views, in the technical sense of the term; "view" here means only an abstract perspective that can be useful for understanding
DBURIType. You can think of
DBURIType as providing a way to visualize and access the database as if it were XML data.
DBURIType does not just provide an exercise in visualization and an additional means to access database data. Each "XML view" can be realized as an XML document – that is, you can use
DBURIType to generate XML documents using database data.
All of this is another way of saying that
DBURIType lets you use XPath notation to 1) address and access any database data to which you have access and 2) construct XML representations of that data.
Figure 19-1 illustrates the relation between a relational table,
hr.employees, a corresponding "XML view" of a portion of that table, and the corresponding DBUri URI (a simple XPath expression). In this case, the portion of the data exposed as XML is the row where
200. The URI can be used to access the data and construct an XML document that reflects the "XML view".
The XML elements in the "XML view" and the steps in the URI XPath expression both reflect the database table and column names. Note the use of
ROW to indicate a row in the database table – both in the "XML view" and in the URI XPath expression.
Note also that the XPath expression contains a root-element step,
oradb. This is used to indicate that the URI corresponds to a DBUri, not an HTTPUri or an XDBUri. Whenever this correspondence is understood from context, this XPath step can be skipped. For example, if it is known that the path in question is a path to database data, the following URIs are equivalent:
Whenever the URI context is not clear, however, you must use the prefix
/oradb to distinguish a URI as corresponding to a DBUri. In particular, you must supply the prefix to
URIFACTORY methods and to DBUriServlet.
Chapter 16, "Generating XML Data from the Database" for other ways to generate XML from database data
An XPath expression is a path into XML data that addresses one or more XML nodes. A DBUri exploits the notion of a virtual XML user visualization of the database to use a simple form of XPath expression as a URI to address database data. This is so, regardless of the type of data, in particular, whether or not the data is XML.
DBURIType, Oracle Database does not support the full XPath or XPointer syntax; only a subset is allowed. There are no syntax restrictions for XDBUri XPath expressions. There is also an exception in the DBUri case: data in
XMLType tables. For an
XMLType table, the simple XPath form is used to address the table itself within the database. Then, to address particular XML data in the table, the remainder of the XPath expression can use the full XPath syntax. This exception applies only to
XMLType tables, not to
In any case, unlike an XDBUri, a DBUri URI does not use a number-sign (
#) to separate the URL portion of a URI from a fragment (XPath) portion.
DBURIType does not use URI fragments; the entire URI is treated as a (simple) XPath expression.
You can create DBUris to any database data to which you have access. XPaths such as the following are allowed:
In the last case,
XMLType_table is an
XMLType table, and
XPath_expression is any XPath expression. For tables that are not
XMLType, a DBUri XPath expression must end at a column; it cannot address specific data inside a column. This restriction includes
XMLType columns, LOB columns, and
VARCHAR2 columns that contain XML data.
A DBUri XPath expression can do any of the following:
Target an entire table.
/HR/EMPLOYEES targets table
employees of database schema
Include XPath predicates at any step in the path, except the database schema and table steps.
/HR/EMPLOYEES/ROW[EMPLOYEE_ID=200]/EMAIL targets the
text() XPath node test on data with scalar content. This is the only node test that can be used, and it cannot be used with the table or row step.
The following can be used in DBUri (XPath) predicate expressions:
A DBUri XPath expression must do all of the following:
Use only the child XPath axis – other axes, such as parent, are not allowed.
Either specify a database schema or specify
PUBLIC to resolve the table name without a specific schema.
Specify a database view or table name.
ROW step, if a database column is targeted.
Identify a single data value, which can be an object-type instance or a collection.
Result in well-formed XML when it is used to generate XML data using database data.
An example of a DBUri that does not result in well-formed XML is
/HR/EMPLOYEES/ROW/LAST_NAME. It returns more than one
<LAST_NAME> element fragment, with no single root element.
Use none of the following:
// (descendent or self)
XPath functions, such as
A DBUri XPath expression can optionally be prefixed by
/dburi (the two are equivalent) to distinguish it. This prefix is case-insensitive. However, the rest of the DBUri XPath expression is case-sensitive, as are XPaths generally. Thus, for example, to specify database column
hr.employees as a DBUri XPath expression, you must use
hr/employees (or a mixed-case combination), because table and column names are uppercase, by default.
http://www.w3.org/TR/xpathon XPath notation
The content of the "XML views" you have of the database, and hence of the XML documents that you can construct, reflects the permissions you have to access particular database data at a given time. That is, a DBUri is scoped to a given database session, so the same DBUri can give different results in the same query, depending on the session context (which user is connected and what privileges the user has).
To complicate things a bit, there is also an XML element
PUBLIC, under which database data is accessible without any database-schema qualification. This is a convenience feature, but it can also lead to some confusion if you forget that the XML views of the database for a given user depend on the specific access the user has to the database at a given time.
PUBLIC corresponds to the use of a public synonym. For example, when queried by user
quine, the following query tries to match table
foo under database schema
quine, but if no such table exists, it tries to match a public synonym named
SELECT * FROM foo;
In the same way, XML element
PUBLIC contains all of the database data visible to a given user, as well as all of the data visible to that user through public synonyms. So, the same DBUri URI
/PUBLIC/FOO can resolve to
quine.foo when user
quine is connected, and resolve to
curry.foo when user
curry is connected.
A DBUri can identify a table, a row, a column in a row, or an attribute of an object column. The following sections describe how to target different object types.
You can target a complete database table, using this syntax:
In this example, a DBUri targets a complete table. An XML document is returned that corresponds to the table contents. The top-level XML element is named for the table. The values of each row are enclosed in a
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (DBURIType.createURI('/HR/EMPLOYEES')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() --------------- <?xml version="1.0"?> <EMPLOYEES> <ROW> <EMPLOYEE_ID>100</EMPLOYEE_ID> <FIRST_NAME>Steven</FIRST_NAME> <LAST_NAME>King</LAST_NAME> <EMAIL>SKING</EMAIL> <PHONE_NUMBER>515.123.4567</PHONE_NUMBER> <HIRE_DATE>17-JUN-87</HIRE_DATE> <JOB_ID>AD_PRES</JOB_ID> <SALARY>24000</SALARY> <DEPARTMENT_ID>90</DEPARTMENT_ID> </ROW> <ROW> <EMPLOYEE_ID>101</EMPLOYEE_ID> <FIRST_NAME>Neena</FIRST_NAME> <LAST_NAME>Kochhar</LAST_NAME> <EMAIL>NKOCHHAR</EMAIL> <PHONE_NUMBER>515.123.4568</PHONE_NUMBER> <HIRE_DATE>21-SEP-89</HIRE_DATE> <JOB_ID>AD_VP</JOB_ID> <SALARY>17000</SALARY> <MANAGER_ID>100</MANAGER_ID> <DEPARTMENT_ID>90</DEPARTMENT_ID> </ROW> . . . 1 row selected.
You can target one or more specific rows of a table, using this syntax:
In this example, a DBUri targets a single table row. The XPath predicate expression identifies the single table row that corresponds to employee number 200. The result is an XML document with
ROW as the top-level element.
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (DBURIType.createURI('/HR/EMPLOYEES/ROW[EMPLOYEE_ID=200]')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() ------------------------------------------------------- <?xml version="1.0"?> <ROW> <EMPLOYEE_ID>200</EMPLOYEE_ID> <FIRST_NAME>Jennifer</FIRST_NAME> <LAST_NAME>Whalen</LAST_NAME> <EMAIL>JWHALEN</EMAIL> <PHONE_NUMBER>515.123.4444</PHONE_NUMBER> <HIRE_DATE>17-SEP-87</HIRE_DATE> <JOB_ID>AD_ASST</JOB_ID> <SALARY>4400</SALARY> <MANAGER_ID>101</MANAGER_ID> <DEPARTMENT_ID>10</DEPARTMENT_ID> </ROW> 1 row selected.
You can target a specific column, using this syntax:
You can target a specific attribute of an object column, using this syntax:
You can target a specific object column whose attributes have specific values, using this syntax:
In this example, a DBUri targets column
last_name for the same employee as in Example 19-7. The top-level XML element is named for the targeted column.
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (DBURIType.createURI('/HR/EMPLOYEES/ROW[EMPLOYEE_ID=200]/LAST_NAME')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() ------------------------------ <?xml version="1.0"?> <LAST_NAME>Whalen</LAST_NAME> 1 row selected.
In this example, a DBUri targets a
CUST_ADDRESS object column containing city and postal code attributes with certain values. The top-level XML element is named for the column, and it contains child elements for each of the object attributes.
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (DBURIType.createURI( '/OE/CUSTOMERS/ROW[CUST_ADDRESS/CITY="Poughkeepsie" and CUST_ADDRESS/POSTAL_CODE=12601]/CUST_ADDRESS')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() --------------- <?xml version="1.0"?> <CUST_ADDRESS> <STREET_ADDRESS>33 Fulton St</STREET_ADDRESS> <POSTAL_CODE>12601</POSTAL_CODE> <CITY>Poughkeepsie</CITY> <STATE_PROVINCE>NY</STATE_PROVINCE> <COUNTRY_ID>US</COUNTRY_ID> </CUST_ADDRESS> 1 row selected.
The DBUri identifies the object that has a
CITY attribute with
Poughkeepsie as value and a
POSTAL_CODE attribute with
12601 as value.
In many cases, it can be useful to retrieve only the text values of a column and not the enclosing tags. For example, if XSLT style sheets are stored in a
CLOB column, you can retrieve the document text without having any enclosing column-name tags. You can use the
text() XPath node test for this. It specifies that you want only the text value of the node. Use the following syntax:
This example retrieves the text value of the employee
last_name column for employee number 200, , without the XML tags.
CREATE TABLE uri_tab (url URIType); Table created. INSERT INTO uri_tab VALUES (DBURIType.createURI( '/HR/EMPLOYEES/ROW[EMPLOYEE_ID=200]/LAST_NAME/text()')); 1 row created. SELECT e.url.getClob() FROM uri_tab e; E.URL.GETCLOB() --------------- Whalen 1 row selected.
You can target a database collection, such as a varray or nested table. You must, however, target the entire collection – you cannot target individual members of a collection. When a collection is targeted, the XML document produced by the DBUri contains each collection member as an XML element, with all such elements enclosed in a element named for the type of the collection.
In this example, a DBUri targets a collection of numbers. The top-level XML element is named for the collection, and its children are named for the collection type (
CREATE TYPE num_collection AS VARRAY(10) OF NUMBER; / Type created. CREATE TABLE orders (item VARCHAR2(10), quantities num_collection); Table created. INSERT INTO orders VALUES ('boxes', num_collection(3, 7, 4, 9)); 1 row created. SELECT * FROM orders; ITEM ---- QUANTITIES ---------- boxes NUM_COLLECTION(3, 7, 4, 9) 1 row selected. SELECT DBURIType('/HR/ORDERS/ROW[ITEM="boxes"]/QUANTITIES').getClob() FROM DUAL; DBURITYPE('/HR/ORDERS/ROW[ITEM="BOXES"]/QUANTITIES').GETCLOB() -------------------------------------------------------------- <?xml version="1.0"?> <QUANTITIES> <NUMBER>3</NUMBER> <NUMBER>7</NUMBER> <NUMBER>4</NUMBER> <NUMBER>9</NUMBER> </QUANTITIES> 1 row selected.
You can use PL/SQL package
URIFACTORY to do more than create
URIType instances. Additional methods are listed in Table 19-2.
Returns the URL of the
Escapes the URI string by replacing characters that are not permitted in URIs by their equivalent escape sequence.
Unescapes a given URI.
Registers a particular type name for handling a particular URL. This is called by
A Boolean argument can be used to indicate that the prefix must be stripped off before calling the appropriate type constructor.
Unregisters a URL handler.
Of particular note is that you can use package
URIFACTORY to define new subtypes of type
URIType. You can then use those subtypes to provide specialized processing of URIs. In particular, you can define
URIType subtypes that correspond to particular protocols –
URIFACTORY will then recognize and process instances of those subtypes accordingly.
Defining new types and creating database columns specific to the new types has these advantages:
It provides an implicit constraint on the columns to contain only instances of those types. This can be useful for implementing specialized indexes on a column for specific protocols. For a DBUri, for instance, you can implement specialized indexes that fetch data directly from disk blocks, rather than executing SQL queries.
You can have different constraints on different columns, based on the type. For a HTTPUri, for instance, you can define proxy and firewall constraints on a column, so that any access through the HTTP uses the proxy server.
To provide specialized processing of URIs, you define and register a new URIType subtype, as follows:
Create the new type using SQL statement
CREATE TYPE. The type must implement method
Optionally override the default methods, to perform specialized processing when retrieving data or to transform the XML data before displaying it.
Choose a new URI prefix, to identify URIs that use this specialized processing.
Register the new prefix using method
registerURLHandler(), so that package
URIFACTORY can create an instance of your new subtype when it receives a URI starting with the new prefix you defined.
After the new subtype is defined, a URI with the new prefix will be recognized by
URIFACTORY methods, and you can create and use instances of the new type.
For example, suppose that you define a new protocol prefix,
ecom://, and define a subtype of
URIType to handle it. Perhaps the new subtype implements some special logic for method
getCLOB(), or perhaps it makes some changes to XML tags or data in method
getXML(). After you register prefix
URIFACTORY, a call to
getURI() will generate an instance of the new
URIType subtype for a URI with that prefix.
This example creates a new type,
ECOMURIType, to handle a new protocol,
ecom://. The example stores three different kinds of URIs in a single table: an HTTPUri, a DBUri, and an instance of the new type,
ECOMURIType. To actually run this example, you would need to define each of the
ECOMURIType member functions.
CREATE TABLE url_tab (urlcol varchar2(80)); Table created. -- Insert an HTTP URL reference INSERT INTO url_tab VALUES ('http://www.oracle.com/'); 1 row created. -- Insert a DBUri INSERT INTO url_tab VALUES ('/oradb/HR/EMPLOYEES/ROW[FIRST_NAME="Jack"]'); 1 row created. -- Create a new type to handle a new protocol called ecom:// -- This is just an example template. For this to run, the implementations -- of these functions needs to be specified. CREATE OR REPLACE TYPE ECOMURIType UNDER SYS.URIType ( OVERRIDING MEMBER FUNCTION getClob RETURN CLOB, OVERRIDING MEMBER FUNCTION getBlob RETURN BLOB, OVERRIDING MEMBER FUNCTION getExternalURL RETURN VARCHAR2, OVERRIDING MEMBER FUNCTION getURI 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:// prefixes BEGIN -- The handler type name is ECOMURIType; schema is HR -- 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 method createURI(), -- so that the string 'ecom://' is not stored inside the -- ECOMURIType object. It is added back automatically when -- you call ECOMURIType.getURI(). URIFACTORY.registerURLHandler (prefix => 'ecom://', schemaname => 'HR', typename => 'ECOMURITYPE', ignoreprefixcase => TRUE, stripprefix => TRUE); END; / PL/SQL procedure successfully completed. -- Insert this new type of URI into the table INSERT INTO url_tab VALUES ('ECOM://company1/company2=22/comp'); 1 row created. -- Use the factory to generate an instance of the appropriate -- subtype for each URI in the table. -- You would need to define the member functions for this to work: SELECT urifactory.getURI(urlcol) FROM url_tab; -- This would generate: HTTPURIType('www.oracle.com'); -- an HTTPUri DBURIType('/oradb/HR/EMPLOYEES/ROW[FIRST_NAME="Jack"]', null); -- a DBUri ECOMURIType('company1/company2=22/comp'); -- an ECOMURIType instance
You can create a DBUri by providing an XPath expression to constructor
DBURIType or to appropriate
URIFACTORY methods. With SQL function
sys_DburiGen, you can alternatively create a DBUri with an XPath that is composed from database columns and their values.
sys_DburiGen takes as its argument one or more database columns or attributes, and optionally a rowid, and generates a DBUri that targets a particular column or row object. Function
sys_DburiGen takes an additional parameter that indicates whether the text value of the node is needed. See Figure 19-2.
All columns or attributes referenced must reside in the same table. They must each reference a unique value. If you specify multiple columns, then the initial columns identify the row, and the last column identifies the column within that row. If you do not specify a database schema, then the table name is interpreted as a public synonym.
See Also:Oracle Database SQL Reference
This example uses SQL function
sys_DburiGen to generate a DBUri that targets column
SELECT sys_DburiGen(employee_id, email) FROM employees WHERE employee_id = 206; SYS_DBURIGEN(EMPLOYEE_ID,EMAIL)(URL, SPARE) ------------------------------------------------------------------- DBURITYPE('/PUBLIC/EMPLOYEES/ROW[EMPLOYEE_ID = "206"]/EMAIL', NULL) 1 row selected.
A column or attribute passed to SQL function
sys_DburiGen must obey the following rules:
Same table: All columns referenced in function
sys_DburiGen must come from the same table or view.
Unique mapping: The column or object attribute must be uniquely mappable back to the table or view from which it came. The only virtual columns allowed are those produced with
REF. The column can come from a subquery with SQL function
table or from an inline view (as long as the inline view does not rename the columns).
Key columns: Either the rowid or a set of key columns must be specified. The list of key columns is not required to be declared as a unique or primary key, as long as the columns uniquely identify a particular row in the result.
PUBLIC element: If the table or view targeted by the rowid or key columns does not specify a database schema, then the
PUBLIC keyword is used. When a DBUri is accessed, the table name resolves to the same table, synonym, or database view that was visible by that name when the DBUri was created.
SELECT sys_DburiGen(employee_id, last_name, 'text()') FROM hr.employees, WHERE employee_id=200;
This will construct a DBUri with the following URI:
Single-column argument: If there is a single-column argument, then the column is used as both the key column to identify the row and the referenced column.
This query uses
employee_id as both the key column and the referenced column. It generates a DBUri that targets the row with
SELECT sys_DburiGen(employee_id) FROM employees WHERE employee_id=200; SYS_DBURIGEN(EMPLOYEE_ID)(URL, SPARE) ------------------------------------- DBURITYPE('/PUBLIC/EMPLOYEES/ROW[EMPLOYEE_ID=''200'']/EMPLOYEE_ID', NULL) 1 row selected.
CREATE TABLE doc_list_tab(docno NUMBER PRIMARY KEY, doc_ref SYS.DBURIType); Table created. -- Insert a DBUri that targets the row with employee_id=177 INSERT INTO doc_list_tab VALUES(1001, (SELECT sys_DburiGen(rowid, employee_id) FROM employees WHERE employee_id=177)); 1 row created. -- Insert a DBUri that targets the last_name column of table employees INSERT INTO doc_list_tab VALUES(1002, (SELECT sys_DburiGen(employee_id, last_name) FROM employees WHERE employee_id=177)); 1 row created. SELECT * FROM doc_list_tab; DOCNO ---------- DOC_REF(URL, SPARE) ----------------------------------------------------- 1001 DBURITYPE('/PUBLIC/EMPLOYEES/ROW[ROWID=''AAAL3LAAFAAAABSABN'']/EMPLOYEE_ID', NULL) 1002 DBURITYPE('/PUBLIC/EMPLOYEES/ROW[EMPLOYEE_ID=''177'']/LAST_NAME', NULL) 2 rows selected.
When selecting from a large column, you might sometimes 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 travel stories are stored in a table, and users search for a set of relevant stories, then you do not want to list each entire story in the search-result page. Instead, you might show just the first 20 characters of each story, to represent the gist, and then return a URL to the full story. This can be done as follows:
Assume that the travel story table is defined as follows:
CREATE TABLE travel_story (story_name VARCHAR2(100), story CLOB); Table created. INSERT INTO travel_story VALUES ('Egypt', 'This is the story of my time in Egypt....'); 1 row created.
We create a function that returns only the first 20 characters from the story:
CREATE OR REPLACE FUNCTION charfunc(clobval IN CLOB) RETURN VARCHAR2 IS res VARCHAR2(20); amount NUMBER := 20; BEGIN DBMS_LOB.read(clobval, amount, 1, res); RETURN res; END; / Function created.
We next create a view that selects only the first twenty characters from the story, and returns a DBUri to the story column.
CREATE OR REPLACE VIEW travel_view AS SELECT story_name, charfunc(story) short_story, sys_DburiGen(story_name, story, 'text()') story_link FROM travel_story; View created. SELECT * FROM travel_view; STORY_NAME ---------- SHORT_STORY ----------- STORY_LINK(URL, SPARE) ---------------------- Egypt This is the story of DBURITYPE('/PUBLIC/TRAVEL_STORY/ROW[STORY_NAME=''Egypt'']/STORY/text()', NULL) 1 row selected.
In this example, whenever a document is inserted into table
clob_tab, its URL is inserted into table
uri_tab. This is done using SQL function
sys_DburiGen in the
RETURNING clause of the
CREATE TABLE clob_tab (docid NUMBER, doc CLOB); Table created. CREATE TABLE uri_tab (docs SYS.DBURIType); Table created.
In PL/SQL, we specify the storage of the URL of the inserted document as part of the insertion operation, using the
RETURNING clause and
EXECUTE IMMEDIATE :
DECLARE ret SYS.DBURIType; BEGIN -- execute the insert operation and get the URL EXECUTE IMMEDIATE 'INSERT INTO clob_tab VALUES (1, ''TEMP CLOB TEST'') RETURNING sys_DburiGen(docid, doc, ''text()'') INTO :1' RETURNING INTO ret; -- Insert the URL into uri_tab INSERT INTO uri_tab VALUES (ret); END; / SELECT e.docs.getURL() FROM hr.uri_tab e; E.DOCS.GETURL() ------------------------------------------------ /ORADB/PUBLIC/CLOB_TAB/ROW[DOCID='1']/DOC/text() 1 row selected.
Oracle XML DB Repository resources can be retrieved using the HTTP server that is incorporated in Oracle XML DB. Oracle Database also includes a servlet, DBUriServlet, that makes any kind of database data available through HTTP(S) URLs. The data can be returned as plain text, HTML, or XML.
A Web client or application can access such data without using SQL or a specialized database API. You can retrieve the data by linking to it on a Web page or by requesting it through HTTP-aware APIs of Java, PL/SQL, and Perl. You can display or process the data using an application such as a Web browser or an XML-aware spreadsheet. DBUriServlet can generate content that is XML data or not, and it can transform the result using XSLT style sheets.
You make database data Web-accessible by using a URI that is composed of a servlet address (URL) plus a DBUri URI that specifies which database data to retrieve. This is the syntax, where
server:port is the URL of the servlet (machine and port), and
table is the DBUri URI (any DBUri URI can be used):
When using XPath notation in a URL for the servlet, you might need to escape certain characters. You can use
getExternalURL() to do this.
You can either use DBUriServlet, which is preinstalled as part of Oracle XML DB, or write your own servlet that runs on a servlet engine. The servlet reads the URI portion of the invoking URL, creates a DBUri using that URI, calls
URIType methods to retrieve the data, and returns the values in a form such as a Web page, an XML document, or a plain-text document.
The MIME type to use is specified to the servlet through the URI:
By default, the servlet produces MIME types
text/plain. If the DBUri path ends in
text/plain is used; otherwise, an XML document is generated with MIME type
You can override the default MIME type, setting it to
binary/x-jpeg or some other value, by using the
contenttype argument to the servlet.
See Also:Chapter 27, "Writing Oracle XML DB Applications in Java", for information on Oracle XML DB servlets
To retrieve the
employee_id column of the
employee table, you can use a URL such as one of the following, where computer
server.oracle.com is running Oracle Database with a Web service listening to requests on port 8080. Step
oradb is the virtual path that maps to the servlet.
-- Produces a content type of text/plain http://server.oracle.com:8080/oradb/QUINE/A/ROW[B=200]/C/text() -- Produces a content type of text/xml http://server.oracle.com:8080/oradb/QUINE/A/ROW[B=200]/C
To override the content type, you can use a URL that passes
text/html to the servlet as the
-- Produces a content type of text/html http://server.oracle.com:8080/oradb/QUINE/A/ROW[B=200]/C?contenttype=text/html
Table 19-3 describes each of the optional URL parameters you can pass to DBUriServlet to customize its output.
Changes the default root tag name for the XML document. For example:
This can also be used to put a tag around a URI that points to multiple rows. For example:
Specifies the MIME type of the generated document. For example:
Passes a URL to
DBUriServlet is built into the database – to customize the servlet, you must edit the Oracle XML DB configuration file,
xdbconfig.xml. You can edit it as the Oracle XML DB user (
XDB), using WebDAV, FTP, Oracle Enterprise Manager, or PL/SQL. To update the file using FTP or WebDAV, download the document, edit it, and save it back into the database.
DBUriServlet is installed at
/oradb/*, which is the address specified in the
servlet-pattern tag of
xdbconfig.xml. The asterisk (
*) is necessary to indicate that any path following
oradb is to be mapped to the same servlet.
oradb is published as the virtual path. You can change the path that will be used to access the servlet.
In this example, the configuration file is modified to install DBUriServlet under
DECLARE doc XMLType; doc2 XMLType; BEGIN doc := DBMS_XDB.cfg_get(); SELECT updateXML(doc, '/xdbconfig/sysconfig/protocolconfig/httpconfig/webappconfig/servletconfig/ servlet-mappings/servlet-mapping[servlet-name="DBUriServlet"]/servlet-pattern/ text()', '/dburi/*') INTO doc2 FROM DUAL; DBMS_XDB.cfg_update(doc2); COMMIT; END; /
Security parameters, the servlet display-name, and the description can also be customized in configuration file
xdbconfig.xml . The servlet can be removed by deleting its servlet-pattern. This can also be done using SQL function
updateXML to update the servlet-mapping element to
Servlet security is handled by Oracle Database using roles. When users log in to the servlet, they use their database username and password. The servlet checks to ensure that the user logging has one of the roles specified in the configuration file using parameter
security-role-ref). By default, the servlet is available to role
authenticatedUser, and any user who logs into the servlet with a valid database password has this role.
The role parameter can be changed to restrict access to any specific database roles. To change from the default
authenticated-user role to a role that you have created, you modify the Oracle XML DB configuration file.
This example changes the default
authenticated-user role to role
servlet-users (which it is assumed you have created).
DECLARE doc XMLType; doc2 XMLType; doc3 XMLType; BEGIN doc := DBMS_XDB.cfg_get(); SELECT updateXML(doc, '/xdbconfig/sysconfig/protocolconfig/httpconfig/webappconfig/servletconfig/ servlet-list/servlet[servlet-name="DBUriServlet"]/security-role-ref/role-name/ text()', 'servlet-users') INTO doc2 FROM DUAL; SELECT updateXML(doc2, '/xdbconfig/sysconfig/protocolconfig/httpconfig/webappconfig/servletconfig/ servlet-list/servlet[servlet-name="DBUriServlet"]/security-role-ref/role-link/ text()', 'servlet-users') INTO doc3 FROM DUAL; DBMS_XDB.cfg_update(doc3); COMMIT; END; /
A URL such as
oradb is handled by DBUriServlet (or by a custom servlet). When a URL such as this is stored as a
URIType instance, it is generally desirable to use subtype
DBURIType, since this URI targets database data.
However, if a
URIType instance is created using methods of package
URIFACTORY such as
getURI(), then by default the subtype used is
DBURIType. This is because
URIFACTORY looks only at the URI prefix, sees
http://, and assumes that the URI targets a Web page. This results in unnecessary layers of communication and perhaps extra character conversions.
To make things more efficient, you can teach
URIFACTORY that URIs of the given form represent database accesses and so should be realized as DBUris, not HTTPUris. You do this by registering a handler for this URI as a prefix, specifying
DBURIType as the type of instance to generate.
This example effectively tells
URIFACTORY that any URI string starting with
/oradb corresponds to a database access.
BEGIN URIFACTORY.registerURLHandler('http://server/servlets/oradb', 'SYS', 'DBURIType', true, true); END; /
After you execute this code, all
getURI() calls in the same session automatically create DBUris for any URI strings with prefix
See Also:Oracle Database PL/SQL Packages and Types Reference for information on