7 XML Schema Storage and Query: Basic

Why XML Schema?

XMLType is an abstract data type that facilitates storing XML data in database columns and tables. XML Schema offers you additional storage and access options for XML data. You can use XML schemas to define which XML elements and attributes, which kinds of element nesting, and which data types can be used.

XML Schema lets you verify that your XML data conforms to its intended definition: the data is validated against the XML schemas that define its proper structure. This definition includes data types, numbers of allowed item occurrences, and allowed lengths of items. When storing XML Schema-based documents in Oracle XML DB using protocols such as FTP or HTTP(S), the XML schema information can improve the efficiency of document insertion. When XML instances must be handled without any prior information about them, XML schemas can be useful in predicting optimum storage, fidelity, and access.

You can take advantage of XML Schema, including its strong typing, for XML data that is unstructured, semi-structured, or structured by storing it as binary XML.

If your XML data is highly structured, then consider storing it object-relationally. In that case, XML Schema is used to efficiently map XML (Schema) data types to SQL data types and object-relational tables and columns.

DTD Support in Oracle XML DB

A DTD is a set of rules that define the allowable structure of an XML document. DTDs are text files that derive their format from SGML and can be associated with an XML document either by using the DOCTYPE element or by using an external file through a DOCTYPE reference. In addition to supporting XML Schema, which provides a structured mapping to object-relational storage or binary XML storage, Oracle XML DB also supports DTD specifications in XML instance documents. Though DTDs are not used to derive the mapping, XML processors can still access and interpret the DTDs.

Registering an XML Schema with Oracle XML DB

The main parameters to procedure DBMS_XMLSCHEMA.registerSchema are these:

• SCHEMAURL – the XML schema URL. This is a unique identifier for the XML schema within Oracle XML DB. It is conventionally in the form of a URL, but this is not a requirement. The XML schema URL is used with Oracle XML DB to identify instance documents, by making the schema location hint identical to the XML schema URL. Oracle XML DB never tries to access a Web server identified by the specified URL.

  Note:

  You cannot register an XML schema using the same SCHEMAURL as any system-defined XML schema.

• SCHEMADOC – The XML schema source document. This is a VARCHAR, CLOB, BLOB, BFILE, XMLType, or URIType value.

• CSID – The character-set ID of the source-document encoding, when schemaDoc is a BFILE or BLOB value.

• OPTIONS – Options that specify how the XML schema should be registered. The most important option is REGISTER_BINARYXML, which indicates that the XML schema is used for binary XML storage. Another option is REGISTER_NT_AS_IOT, which forces OCTs to be stored as index-organized tables (IOTs).

  Note:

  If you specify option REGISTER_BINARYXML, then you must also set parameter GENTYPES to FALSE.

The code in Example 7-3 registers the XML schema at URL http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd. This example shows how to register an XML schema using the BFILE mechanism to read the source document from a file on the local file system of the database server.

BEGIN
  DBMS_XMLSCHEMA.registerSchema(
    SCHEMAURL => 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd',
    SCHEMADOC => bfilename('XMLDIR','purchaseOrder.xsd'),
    CSID      => nls_charset_id('AL32UTF8'));
END;
/

Delete and Reload Documents Before Registering Their XML Schema

When you register an XML schema, keep in mind that the act of registering a schema has no effect on the status of any instance documents already loaded into Oracle XML DB Repository that reference the XML schema. Because the XML schema was not yet registered, such instance documents were non-schema-based when they were loaded. They remain non-schema-based after the schema is registered.

You must delete such instance documents, and reload them after registering the schema, in order to obtain schema-based documents.

Storage and Access Infrastructure

As part of registering an XML schema, Oracle XML DB also performs several tasks that facilitate storing, accessing, and manipulating XML instances that conform to the XML schema. These steps include:

• Mapping XML Schema data types to Oracle XML DB storage. When XML schema-based data is stored, its storage data types are derived from the XML Schema data types using a default mapping and, optionally, using mapping information that you specify using XML schema annotations. For binary XML storage, XML Schema types are mapped to binary XML encoding types. For object-relational storage, XML schema registration creates the appropriate SQL object types for the structured storage of conforming documents.

• Creating default tables. XML schema registration generates default XMLType tables for all global elements. You can use XML-schema annotations to control the names of the tables, and to provide column-level and table-level storage clauses and constraints for use during table creation.

  See Also:

  • "Mapping XML Schema Data Types to Oracle XML DB Storage"

  • "Default Tables Created During XML Schema Registration"

  • "Oracle XML Schema Annotations"

After XML schema registration, documents that reference the XML schema using the XML Schema instance mechanism can be processed automatically by Oracle XML DB. For XML data that is stored object-relationally, XMLType tables and columns can be created that are constrained to the global elements defined by the XML schema.

Atomic Nature of XML Schema Registration

Like all DDL operations, XML schema registration is non-transactional. However, registration is atomic, in this sense:

• If registration succeeds, then the operation is auto-committed.

• If registration fails, then the database is rolled back to the state before registration began.

Because XML schema registration potentially involves creating object types and tables, error recovery involves dropping any types and tables thus created. The entire XML schema registration process is guaranteed to be atomic: either it succeeds or the database is restored to its state before the start of registration.

Managing and Storing XML Schemas

XML schema documents are themselves stored in Oracle XML DB as XMLType instances. XML schema-related XMLType types and tables are created as part of the Oracle XML DB installation script, catxdbs.sql.

The XML schema for Oracle XML DB XML schemas is called the root XML Schema, XDBSchema.xsd. The root XML schema describes any valid XML schema that can be registered with Oracle XML DB. You can access XDBSchema.xsd at Oracle XML DB Repository location /sys/schemas/PUBLIC/xmlns.oracle.com/xdb/XDBSchema.xsd.

Debugging XML Schema Registration for XML Data Stored Object-Relationally

For XML data stored object-relationally, you can monitor the object types and tables created during XML schema registration by setting the following event before invoking PL/SQL procedure DBMS_XMLSCHEMA.registerSchema:

ALTER SESSION SET EVENTS = '31098 TRACE NAME CONTEXT FOREVER'

Setting this event causes the generation of a log of all of the CREATE TYPE and CREATE TABLE statements. This log is written to the user session trace file, typically found in ORACLE_BASE/diag/rdbms/ORACLE_SID/ORACLE_SID/udump. This script can be a useful aid in diagnosing problems during XML schema registration.

SQL Object Types Created During XML Schema Registration, for Structured Storage

If parameter GENTYPES is TRUE when an XML schema is registered for use with XML data stored object-relationally, then Oracle XML DB creates the appropriate SQL object types that enable structured storage of conforming XML documents. By default, all SQL object types are created in the database schema of the user who registers the XML schema. If annotation xdb:defaultSchema is used, then Oracle XML DB attempts to create the object type using the specified database schema. The current user must have the necessary privileges to create these object types.

Example 7-4 shows the SQL object types that are created automatically when XML schema purchaseOrder.xsd is registered with Oracle XML DB.

DESCRIBE "PurchaseOrderType1668_T"
  
"PurchaseOrderType1668_T" is NOT FINAL
Name                 Null?  Type
-------------------- ------ -------------------------------
SYS_XDBPD$                  XDB.XDB$RAW_LIST_T
Reference                   VARCHAR2(30 CHAR)
Actions                     ActionsType1661_T
Reject                      RejectionType1660_T
Requestor                   VARCHAR2(128 CHAR)
User                        VARCHAR2(10 CHAR)
CostCenter                  VARCHAR2(4 CHAR)
ShippingInstructions        ShippingInstructionsTyp1659_T
SpecialInstructions         VARCHAR2(2048 CHAR)
LineItems                   LineItemsType1666_T
Notes                       VARCHAR2(4000 CHAR)
 
DESCRIBE "LineItemsType1666_T"
 
"LineItemsType1666_T" is NOT FINAL
Name                 Null? Type
-------------------- ----- -------------------------------
SYS_XDBPD$                 XDB.XDB$RAW_LIST_T
LineItem                   LineItem1667_COLL
 
DESCRIBE "LineItem1667_COLL"

"LineItem1667_COLL" VARRAY(2147483647) OF LineItemType1665_T
"LineItemType1665_T" is NOT FINAL
Name                Null? Type
------------------- ----- --------------------------------
SYS_XDBPD$                XDB.XDB$RAW_LIST_T
ItemNumber                NUMBER(38)
Description               VARCHAR2(256 CHAR)
Part                      PartType1664_T

Default Tables Created During XML Schema Registration

As part of XML schema registration for XML data, you can create default tables. Default tables are most useful when documents conforming to the XML schema are inserted through APIs and protocols such as FTP and HTTP(S) that do not provide any table specification. In such cases, the XML instance is inserted into the default table.

DESCRIBE "purchaseorder1669_tab"

Name                        Null? Type
--------------------------- ----- -----------------------
TABLE of
  SYS.XMLTYPE(
    XMLSchema "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd"
    Element "PurchaseOrder")
  STORAGE OBJECT-RELATIONAL TYPE "PurchaseOrderType1668_T"

If you provide a value for attribute xdb:defaultTable, then the XMLType table is created with that name. Otherwise it is created with an internally generated name.

Any text specified using attributes xdb:tableProps and xdb:columnProps is appended to the generated CREATE TABLE statement.

Generated Names are Case Sensitive

The names of any SQL tables, object, and attributes generated by XML schema registration are case sensitive. For instance, in Example 7-3, a table named PurchaseOrder1669_TAB is created automatically during registration of the XML schema. Because this table name was derived from the element name, PurchaseOrder, the table name is also mixed case. You must therefore refer to this table in SQL code by using a quoted identifier: "PurchaseOrder1669_TAB". Failure to do so results in an object-not-found error, such as ORA-00942: table or view does not exist.

Database Objects That Depend on Registered XML Schemas

The following database objects are dependent on registered XML schemas:

• Tables or views that have an XMLType column that conforms to an element in an XML schema.

• Other XML schemas that include or import a given XML schema as part of their definition.

• Cursors that reference an XML schema. This includes references within functions of package DBMS_XMLGEN. Such cursors are purely transient objects.

Listing All Registered XML Schemas

Example 7-6 shows how to use PL/SQL procedure DBMS_XMLSCHEMA.registerSchema to obtain a list of all XML schemas registered with Oracle XML DB. You can also examine views USER_XML_SCHEMAS, ALL_XML_SCHEMAS, USER_XML_TABLES, and ALL_XML_TABLES.

DESCRIBE DBA_XML_SCHEMAS

Name         Null? Type
------------ ----- -----------------------
OWNER              VARCHAR2(30)
SCHEMA_URL         VARCHAR2(700)
LOCAL              VARCHAR2(3)
SCHEMA             XMLTYPE(XMLSchema "http://xmlns.oracle.com/xdb/XDBSchema.xsd"
                           Element "schema")
INT_OBJNAME        VARCHAR2(4000)
QUAL_SCHEMA_URL    VARCHAR2(767)
HIER_TYPE          VARCHAR2(11)
BINARY             VARCHAR2(3)
SCHEMA_ID          RAW(16)
HIDDEN             VARCHAR2(3)

SELECT OWNER, LOCAL, SCHEMA_URL FROM DBA_XML_SCHEMAS;

OWNER   LOC   SCHEMA_URL
-----   ---   ----------------------
XDB     NO    http://xmlns.oracle.com/xdb/XDBSchema.xsd
XDB     NO    http://xmlns.oracle.com/xdb/XDBResource.xsd
XDB     NO    http://xmlns.oracle.com/xdb/acl.xsd
XDB     NO    http://xmlns.oracle.com/xdb/dav.xsd
XDB     NO    http://xmlns.oracle.com/xdb/XDBStandard.xsd
XDB     NO    http://xmlns.oracle.com/xdb/log/xdblog.xsd
XDB     NO    http://xmlns.oracle.com/xdb/log/ftplog.xsd
XDB     NO    http://xmlns.oracle.com/xdb/log/httplog.xsd
XDB     NO    http://www.w3.org/2001/xml.xsd
XDB     NO    http://xmlns.oracle.com/xdb/XDBFolderListing.xsd
XDB     NO    http://xmlns.oracle.com/xdb/stats.xsd
XDB     NO    http://xmlns.oracle.com/xdb/xdbconfig.xsd
SCOTT   YES   http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd

13 rows selected.

DESCRIBE DBA_XML_TABLES

Name         Null? Type
------------ ----- -----------------------
OWNER              VARCHAR2(30)
TABLE_NAME         VARCHAR2(30)
XMLSCHEMA          VARCHAR2(700)
SCHEMA_OWNER       VARCHAR2(30)
ELEMENT_NAME       VARCHAR2(2000)
STORAGE_TYPE       VARCHAR2(17)
ANYSCHEMA          VARCHAR2(3)
NONSCHEMA          VARCHAR2(3)

SELECT TABLE_NAME FROM DBA_XML_TABLES
  WHERE XMLSCHEMA = 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd';

TABLE_NAME
---------------------
PurchaseOrder1669_TAB

1 row selected.

Deleting an XML Schema

You can delete a registered XML schema by using procedure DBMS_XMLSCHEMA.deleteSchema. This does the following, by default:

1. Checks that the current user has the appropriate privileges to delete the resource corresponding to the XML schema within Oracle XML DB Repository. You can control which users can delete which XML schemas, by setting the appropriate ACLs on the XML schema resources.

2. Checks whether there are any tables dependent on the XML schema that is to be deleted. If so, raises an error and cancels the deletion. This check is not performed if option delete_invalidate or delete_cascade_force is used. In that case, no error is raised.

3. Removes the XML schema document from the Oracle XML DB Repository (folder /sys/schemas).

4. Removes the XML schema document from DBA_XML_SCHEMAS, unless it was registered for use with binary XML instances and neither delete_invalidate nor delete_cascade_force is used.

5. Drops the default table, if either delete_cascade or delete_cascade_force is used. Raises an error if delete_cascade_force is specified and there are instances in other tables that are also dependent on the XML schema.

BEGIN
  DBMS_XMLSCHEMA.deleteSchema(
    SCHEMAURL => 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd',
    DELETE_OPTION => DBMS_XMLSCHEMA.DELETE_CASCADE_FORCE);
END;
/

Local XML Schema

By default, an XML schema belongs to you after you register it with Oracle XML DB. A reference to the XML schema document is stored in Oracle XML DB Repository. Such XML schemas are referred to as local. By default, they are usable only by you, the owner. In Oracle XML DB, local XML schema resources are created under folder /sys/schemas/username. The rest of the repository path name is derived from the schema URL.

BEGIN
  DBMS_XMLSCHEMA.registerSchema(
    SCHEMAURL => 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd',
    SCHEMADOC => bfilename('XMLDIR','purchaseOrder.xsd'),
    LOCAL     => TRUE,
    GENTYPES  => TRUE, 
    GENTABLES => FALSE, 
    CSID      => nls_charset_id('AL32UTF8'));
END;
/

If this local XML schema is registered by user QUINE, it is given this path name:

/sys/schemas/QUINE/xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd

Database users need appropriate permissions and Access Control Lists (ACLs) to create a resource with this path name, in order to register the XML schema as a local XML schema.

Global XML Schema

In contrast to local schemas, a privileged user can register an XML schema as global by specifying an argument in the DBMS_XMLSCHEMA registration function. Global XML schemas are visible to all users. They are stored under folder /sys/schemas/PUBLIC/ in Oracle XML DB Repository.

You can register a local schema with the same URL as an existing global schema. A local schema always shadows (hides) any global schema with the same name (URL). Example 7-9 illustrates registration of a global schema.

GRANT XDBADMIN TO QUINE;

Grant succeeded.

CONNECT quine
Enter password: password

Connected.

BEGIN
  DBMS_XMLSCHEMA.registerSchema(
    SCHEMAURL => 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd',
    SCHEMADOC => bfilename('XMLDIR','purchaseOrder.xsd'),
    LOCAL     => FALSE,
    GENTYPES  => TRUE, 
    GENTABLES => FALSE, 
    CSID      => nls_charset_id('AL32UTF8'));
END;
/

/sys/schemas/PUBLIC/xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd

What is DOM Fidelity?

DOM fidelity means that all information in an XML document is preserved, except whitespace that is insignificant. With DOM fidelity, XML data retrieved from the database has the same information as before it was inserted into the database, with the single exception of insignificant whitespace. The term "DOM fidelity" is used because this kind of fidelity is particularly important for DOM traversals.

With binary XML storage of XML data, all of the significant information is encoded in the binary XML format, ensuring DOM fidelity. With structured storage of XML data, the elements and attributes declared in an XML schema are mapped to separate attributes in the corresponding SQL object types. However, the following information in XML instance documents is not stored in these object attributes:

• Namespace declarations

• Comments

• Prefix information

Instead, Oracle XML DB uses a separate mechanism to keep track of this information: it is recorded as instance-level metadata.

SYS_XDBPD$ and DOM Fidelity for Structured Storage

In order to provide DOM fidelity for XML data stored object-relationally, Oracle XML DB maintains instance-level metadata. This metadata is tracked at the type level using the system-defined binary object attribute SYS_XDBPD$. This object attribute is referred to as the positional descriptor, or PD for short. The PD is intended for Oracle XML DB internal use only. You should never directly access or manipulate column PD.

The positional descriptor stores all information that cannot be stored in any of the other object attributes. PD information is used to ensure the DOM fidelity of all XML documents stored in Oracle XML DB. Examples of PD information include: ordering information, comments, processing instructions, and namespace prefixes.

If DOM fidelity is not required, you can suppress the use of SYS_XDBPD$ by setting attribute xdb:maintainDOM to false in the XML schema, at the type level.

Changing an XML Schema and XML Instance Documents for Translation

This section describes the changes that are required to be made to an XML schema and an associated XML instance document to make the document translatable.

Making XML Documents Translatable

This section uses the translation-specifying XML schema attributes to make elements in a sample document translatable. Example 7-10 shows an XML schema that defines documents that contain a title string that needs to be translatable.

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:xdbsc="http://xmlns.oracle.com/xdb/security.xsd"
        xmlns:xdb="http://xmlns.oracle.com/xdb.xsd"
        targetNamespace="http://xmlns.oracle.com/xdb/security.xsd"
        elementFormDefault="qualified" version="1.0">
  <annotation>
    <documentation>
This XML schema describes the structure of Security Class documents.
    </documentation>
  </annotation>
  <element name="securityClass" xdb:defaultTable="">
    <complexType>
      <sequence>
        <element name="name" type="string"/>
        <element name="title" minOccurs="0" maxOccurs="unbounded"/>
        <element name="inherits-from" type="QName" minOccurs="0" maxOccurs="unbounded"/>
        <element name="privlist" minOccurs="0" maxOccurs="unbounded">
          <complexType>
            <choice minOccurs="0" maxOccurs="unbounded">
              <element ref="xdbsc:privilege"/>
                <element ref="xdbsc:aggregatePrivilege"/>
            </choice>
          </complexType>
        </element>
        <!-- this "any" contains all application specific information
             for a security class in general e.g. reason for creation  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="targetNamespace" type="anyURI" use="required"/>
      <!-- all privileges in this security class are under this target namespace -->
    </complexType>
  </element>
  <element name="aggregatePrivilege">
    <complexType>
      <sequence>
        <element name="title" minOccurs="0" maxOccurs="unbounded"/>
        <sequence maxOccurs="unbounded">
          <element name="privilegeRef">
            <complexType>
              <attribute name="name" type="QName" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             an aggregate privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
  <element name="privilege">
    <complexType>
      <sequence minOccurs="0">
        <element name="title" minOccurs="0" maxOccurs="unbounded"/>
        <sequence minOccurs="0" maxOccurs="unbounded">
          <element name="columnRef">
            <complexType>
              <attribute name="schema" type="string" use="required"/>
              <attribute name="table" type="string" use="required"/>
              <attribute name="column" type="string" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             for a privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
</schema>

Example 7-11 shows a document that is associated with the XML schema of Example 7-10.

<securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
               xmlns:is="xmlns.oracle.com/iStore"
               xmlns:oa="xmlns.oracle.com/OracleApps"
               targetNamespace="xmlns.oracle.com/example">
  <name>
securityClassExample
  </name>
  <title>
Security Class Example
  </title>
  <inherits-from>is:iStorePurchaseOrder</inherits-from>
  <privlist>
  <privilege name="privilege1"/>
  <aggregatePrivilege name="iStorePOApprover">
    <title>
iStore Purchase Order Approver
    </title>
    <privilegeRef name="is:privilege1"/>
    <privilegeRef name="oa:submitPO"/>
    <privilegeRef name="oa:privilege3"/>
  </aggregatePrivilege>
  <privilege name="privilege2">
    <title>
secondary privilege
    </title>
    <columnRef schema="APPS" table="PurchaseOrder" column="POId"/>
    <columnRef schema="APPS" table="PurchaseOrder" column="Amount"/>
  </privilege>
  </privlist>
</securityClass>

To make the top-level title translatable, set xdb:translate to true. This is a single-valued element (xdb:maxOccurs is 1). Example 7-12 shows the new XML schema, where attribute xdb:translate is true.

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:xdbsc="http://xmlns.oracle.com/xdb/security.xsd"
        xmlns:xdb="http://xmlns.oracle.com/xdb.xsd"
        targetNamespace="http://xmlns.oracle.com/xdb/security.xsd"
        elementFormDefault="qualified" version="1.0">
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
        schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:import namespace-"http://xmlns.oracle.com/xdb"
        schemaLocation="http://xmlns.oracle.com/xdb/xmltr.xsd"/>
  <annotation>
    <documentation>
This XML schema describes the structure of Security Class documents.
    </documentation>
  </annotation>
  <element name="securityClass" xdb:defaultTable="">
    <complexType>
      <sequence>
        <element name="name" type="string"/>
        <element ref="titleref" minOccurs="0" maxOccurs="unbounded"
                 xdb:maxOccurs="1" xdb:translate="true"/>
        <element name="inherits-from" type="QName" minOccurs="0" maxOccurs="unbounded"/>
        <element name="privlist" minOccurs="0" maxOccurs="unbounded" xdb:maxOccurs="1">
          <complexType>
            <choice minOccurs="0" maxOccurs="unbounded">
              <element ref="xdbsc:privilege"/>
              <element ref="xdbsc:aggregatePrivilege"/>
            </choice>
          </complexType>
        </element>
        <!-- this "any" contains all application specific information
             for a security class in general e.g. reason for creation  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="targetNamespace" type="anyURI" use="required"/>
      <!-- all privileges in this security class are under this target namespace -->
    </complexType>
  </element>
  <element name="aggregatePrivilege">
    <complexType>
      <sequence>
        <element name="title" minOccurs="0" maxOccurs="unbounded"/>
        <sequence maxOccurs="unbounded">
          <element name="privilegeRef">
            <complexType>
              <attribute name="name" type="QName" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             an aggregate privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
  <element name="privilege">
    <complexType>
      <sequence minOccurs="0">
        <element name="title" minOccurs="0" maxOccurs="unbounded"/>
        <sequence minOccurs="0" maxOccurs="unbounded">
          <element name="columnRef">
            <complexType>
              <attribute name="schema" type="string" use="required"/>
              <attribute name="table" type="string" use="required"/>
              <attribute name="column" type="string" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             for a privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
  <element name="titleref">
    <complexType>
      <simpleContent>
        <extension base="xs:string">
          <attribute ref="xml:lang"/>
          <attribute ref="xdb:srclang"/>
        </extension>
      </simpleContent>
    </complexType>
  </element>
</schema>

Example 7-13 shows an instance document after translation of the title text.

<securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
               xmlns:is="xmlns.oracle.com/iStore"
               xmlns:oa="xmlns.oracle.com/OracleApps">
  <name>
securityClassExample
  </name>
  <title xml:lang="en" xdb:srclang="true">
Security Class Example
  </title>
  <title xml:lang="es">
Security Class Example - Spanish
  </title>
  <title xml:lang="fr">
Security Class Example - French
  </title>    
  <inherits-from>is:iStorePurchaseOrder</inherits-from>
  <privlist>
    <privilege name="privilege1"/>
    <aggregatePrivilege name="iStorePOApprover">
      <title>
iStore Purchase Order Approver
      </title>
      <privilegeRef name="is:privilege1"/>
      <privilegeRef name="oa:submitPO"/>
      <privilegeRef name="oa:privilege3"/>
    </aggregatePrivilege>
    <privilege name="privilege2">
      <title>
secondary privilege
      </title>
      <columnRef schema="APPS" table="PurchaseOrder" column="POId"/>
      <columnRef schema="APPS" table="PurchaseOrder" column="Amount"/>
    </privilege>
  </privlist>
</securityClass>

To make the title translatable in the case of a multi-valued element, you would set xdb:maxOccurs to unbounded. However, xdb:translate cannot be set to true for a multiple-valued element, unless there is an identifier attribute that uniquely identifies each element. Example 7-14 shows an XML schema that uses an identifier attribute id for the title element.

<schema xmlns="http://www.w3.org/2001/XMLSchema"
        xmlns:xdbsc="http://xmlns.oracle.com/xdb/security.xsd"
        xmlns:xdb="http://xmlns.oracle.com/xdb.xsd"
        targetNamespace="http://xmlns.oracle.com/xdb/security.xsd"
        elementFormDefault="qualified" version="1.0">
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
        schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:import namespace-"http://xmlns.oracle.com/xdb"
        schemaLocation="http://xmlns.oracle.com/xdb/xmltr.xsd"/>
  <annotation>
    <documentation>
This XML schema describes the structure of Security Class documents.
    </documentation>
  </annotation>
  <element name="securityClass" xdb:defaultTable="">
    <complexType>
      <sequence>
        <element name="name" type="string"/>
        <element name="title" minOccurs="0" maxOccurs="unbounded" xdb:maxOccurs="1"/>
        <element name="inherits-from" type="QName" minOccurs="0" maxOccurs="unbounded"/>
        <element name="privlist" minOccurs="0" maxOccurs="unbounded" xdb:maxOccurs="1">
          <complexType>
            <choice minOccurs="0" maxOccurs="unbounded">
              <element ref="xdbsc:privilege"/>
              <element ref="xdbsc:aggregatePrivilege"/>
            </choice>
          </complexType>
        </element>
        <!-- this "any" contains all application specific information
             for a security class in general e.g. reason for creation  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="targetNamespace" type="anyURI" use="required"/>
      <!-- all privileges in this security class are under this target namespace -->
    </complexType>
  </element>
  <element name="aggregatePrivilege">
    <complexType>
      <sequence>
        <element name="titleref" minOccurs="0" maxOccurs="unbounded"
                 xdb:maxoccurs="unbounded" xdb:translate="true"/>
        <sequence maxOccurs="unbounded">
          <element name="privilegeRef">
            <complexType>
              <attribute name="name" type="QName" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             an aggregate privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
  <element name="privilege">
    <complexType>
      <sequence minOccurs="0">
        <element name="titleref" minOccurs="0" maxOccurs="unbounded"
                 xdb:maxoccurs="unbounded" xdb:translate="true"/>
        <sequence minOccurs="0" maxOccurs="unbounded">
          <element name="columnRef">
            <complexType>
              <attribute name="schema" type="string" use="required"/>
              <attribute name="table" type="string" use="required"/>
              <attribute name="column" type="string" use="required"/>
            </complexType>
          </element>
          <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
        </sequence>
        <!-- this "any" contains all application specific information   
             for a privilege e.g. translations  -->
        <any namespace="##other" minOccurs="0" maxOccurs="unbounded"/>
      </sequence>
      <attribute name="name" type="string" use="required"/>
    </complexType>
  </element>
  <element name="titleref">
    <complexType>
      <simpleContent>
        <extension base="xs:string">
          <attribute ref="xml:lang"/>
          <attribute ref="xdb:srclang"/>
          <attribute name="id" type="integer"/>
        </extension>
      </simpleContent>
    </complexType>
  </element>
</schema>

Example 7-15 shows a document associated with the XML schema in Example 7-14.

<securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
               xmlns:is="xmlns.oracle.com/iStore"
               xmlns:oa="xmlns.oracle.com/OracleApps">
  <name>
securityClassExample
  </name>
  <title>
Security Class Example
  </title>
  <inherits-from>is:iStorePurchaseOrder</inherits-from>
  <privlist>
    <privilege name="privilege1"/>
    <aggregatePrivilege name="iStorePOApprover">
      <title>
iStore Purchase Order Approver
      </title>
      <privilegeRef name="is:privilege1"/>
      <privilegeRef name="oa:submitPO"/>
      <privilegeRef name="oa:privilege3"/>
    </aggregatePrivilege>
    <privilege name="privilege2">
      <title id="2" xml:lang="en" xdb:srclang="true">
secondary privilege - english
      </title>
      <title id="1" xml:lang="fr">
primary privilege - french
      </title>
      <title id="1" xml:lang="en" xdb:srclang="true">
primary privilege - english
      </title>       
      <columnRef schema="APPS" table="PurchaseOrder" column="POId"/>
      <columnRef schema="APPS" table="PurchaseOrder" column="Amount"/>
    </privilege>
  </privlist>
</securityClass>

Operations on Translated Documents

You can perform the following operations on translated documents:

• Insert: You can insert a document into Oracle XML DB, if it conforms to an XML schema that supports translations. For the document that contains translations, you can either provide the language information or use the session language translation.

  • When the document does not contain the language information and the xml:lang attribute is not set, the session language is used for translation. Example 7-16 describes a document with a session language of Japanese. Attribute xml:lang is set to session language, and attribute xdb:srclang is set to true.

    Example 7-16 Inserting a Document with No Language Information

    <securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
                   xmlns:is="xmlns.oracle.com/iStore"
                   xmlns:oa="xmlns.oracle.com/OracleApps"
                   targetNamespace="xmlns.oracle.com/example">
      <name>
    securityClassExample
      </name>
      <title>
    Security Class Example
      </title>
      <inherits-from>is:iStorePurchaseOrder</inherits-from>
    </securityClass>
    

    Example 7-17 shows the document after it is inserted into Oracle XML DB Repository.

    Example 7-17 Document After Insertion into the Repository

    <securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
                   xmlns:is="xmlns.oracle.com/iStore"
                   xmlns:oa="xmlns.oracle.com/OracleApps"
                   targetNamespace="xmlns.oracle.com/example">
      <name>
    securityClassExample
      </name>
      <title xml:lang="jp" xdb:srclang="true">
    Security Class Example
      </title>
      <inherits-from>is:iStorePurchaseOrder</inherits-from>
    </securityClass>
    

  • When you provide the language information, you set attribute xml:lang by either explicitly marking a translation as xdb:srclang=true or using the session language translation in attribute xdb:srclang. If you do neither, then an arbitrary translation is picked, for which xdb:srclang is set to true.

    Example 7-18 describes a document with a session language of Japanese.

    Example 7-18 Inserting a Document with Language Information

    <securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
                   xmlns:is="xmlns.oracle.com/iStore"
                   xmlns:oa="xmlns.oracle.com/OracleApps"
                   targetNamespace="xmlns.oracle.com/example">
      <name>
    securityClassExample
      </name>
      <title xml:lang="en">
    Security Class Example
      </title>
      <title xml:lang="fr">
    Security Class Example - FR
      </title>
      <inherits-from>is:iStorePurchaseOrder</inherits-from>
    </securityClass>
    

    Example 7-19 shows the document after it is inserted into Oracle XML DB Repository.

    Example 7-19 Document After Insertion

    <securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
                   xmlns:is="xmlns.oracle.com/iStore"
                   xmlns:oa="xmlns.oracle.com/OracleApps"
                   targetNamespace="xmlns.oracle.com/example">
      <name>
    securityClassExample
      </name>
      <title xml:lang="en" xdb:srclang="true">
    Security Class Example
      </title>
      <title xml:lang="fr">
    Security Class Example - FR
      </title>
      <inherits-from>is:iStorePurchaseOrder</inherits-from>
    </securityClass>
    

• Query: If you query nodes that involve translated elements, the query displays the translation's default behavior. In order to specify that the translation's default behavior should be applied to the query result, you need to use the Oracle XPath function ora:translate. This is the syntax of the function:

  Nodeset ora:translate(Nodeset parent, String childname, String childnsp)
  

  Parameter parent is the parent node under which you want to search for the translated nodes; childname is the name of the child node; and childnsp is the namespace URL of the child node.

  Function ora:translate returns a positive integer when the name of the parent node matches the name of the specified child node, and the xml:lang value is same as the session language or the language for which xdb:srclang is true.

  When SQL functions such as XMLQuery are applied to translated documents, they return the session language translation, if present, or the source language translation, otherwise. For example, this query returns the session language translation:

  SELECT XMLQuery('$x/ora:translate(securityClass, "title")'
                  PASSING x.OBJECT_VALUE AS "x" RETURNING CONTENT)
    FROM some_table x;
  

  This is the output of that query:

  <title xml:lang="fr">
  Security Class Example - FR
  </title>
  

  To obtain the result in a particular language, specify it in the XPath expression.

  SELECT XMLQuery('$x/securityClass/title[@xml:lang="en"]'
                  PASSING x.OBJECT_VALUE AS "x" RETURNING CONTENT)
    FROM some_table x;
  

  This is the output of that query:

  <title xml:lang="en" xdb:srclang="true">
  Security Class Example
  </title>
  

  Because you can store translated documents only as text (CLOB) or binary XML, only functional evaluation and queries with a function-based index, an XMLIndex index, or a CONTEXT index are possible. For XMLIndex index and CONTEXT index queries, if the document has a session language translation, then that is returned, otherwise the source language translation is returned. However, for queries with a function-based index, you need to create an index with an explicit xml:lang predicate for every language for which you want to use the index.

  When you retrieve the complete document using SQL functions such as XMLSerialize and XDBURIType, only the translations that match the session language translations are returned. For protocols, you can set your language preferences, and the document is returned in that language only.

  The following PL/SQL procedures and functions support XML translations:

  • DBMS_XMLTRANSLATIONS.translateXML: Translate a document to the specified language. If the specified language translation is present, it is returned, otherwise, the source language translation is returned.

    For example, if you write translateXML(doc, 'fr') to specify French as the translation language for the Example 7-19, it returns the following code and ignores all other translations:

    securityClass xmlns="http://xmlns.oracle.com/xdb/security.xsd"
                   xmlns:is="xmlns.oracle.com/iStore"
                   xmlns:oa="xmlns.oracle.com/OracleApps"
                   targetNamespace="xmlns.oracle.com/example">
        <name>
            securityClassExample
        </name>
        <title xml:lang="fr">
            Security Class Example - FR
        </title>
        <inherits-from>is:iStorePurchaseOrder</inherits-from>
    </securityClass>
    

  • DBMS_XMLTRANSLATIONS.enableTranslation, DBMS_XMLTRANSLATIONS.disableTranslation: Enable or disable translations at the session level. Queries work on the base document if the translation is disabled and on the translated document if it is enabled.

  • DBMS_XMLTRANSLATIONS.getBaseDocument: Returns the entire document, with all of the translations.

• Update: You can use Oracle SQL function updateXML to update the translated nodes. However, an error is raised if you try to update a translated node without specifying the translation language. The following PL/SQL procedures support update operations on translated documents:

  • DBMS_XMLTRANSLATIONS.updateTranslation: This function updates the translation at a specified xpath in a particular language. If the translation in a particular language is not present, then it is inserted.

  • DBMS_XMLTRANSLATIONS.setSourceLang: This procedure sets the source language at a specified xpath to the specified language.

Specifying XMLType Storage Options for XML Schema-Based Data

You can specify storage options to use when you manually create a table that stores XML instance documents that reference an XML schema. To specify a particular XMLType storage model, use a STORE AS clause in the CREATE TABLE statement. Otherwise, the storage model specified during registration of the XML schema is used. If no storage model was specified during registration, then object-relational storage is used.

This section describes what you need to know about specifying storage options for XML schema-based data. You can also specify storage options for tables that are created automatically, by using XML schema annotations.

STORE AS BINARY XML

STORE AS BINARY XML
 XMLSCHEMA ...

STORE AS BINARY XML
 XMLSCHEMA ...
 ALLOW NONSCHEMA

STORE AS BINARY XML
 ALLOW ANYSCHEMA

STORE AS BINARY XML
 ALLOW ANYSCHEMA
 ALLOW NONSCHEMA

CREATE TABLE purchaseorder_as_table OF XMLType
  XMLTYPE STORE AS CLOB
  XMLSCHEMA "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd"
  ELEMENT "PurchaseOrder";
 
CREATE TABLE purchaseorder_as_column (id NUMBER, xml_document XMLType)
  XMLTYPE COLUMN xml_document
  STORE AS CLOB
  XMLSCHEMA "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd"
  ELEMENT "PurchaseOrder";

CREATE TABLE purchaseorder_as_table 
  OF XMLType (UNIQUE ("XMLDATA"."Reference"),
              FOREIGN KEY ("XMLDATA"."User") REFERENCES hr.employees (email))
ELEMENT
  "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd#PurchaseOrder"
  VARRAY "XMLDATA"."LineItems"."LineItem" STORE AS LOB lineitem_lob
  LOB ("XMLDATA"."Notes")
    STORE AS (TABLESPACE USERS ENABLE STORAGE IN ROW 
              STORAGE(INITIAL 4K NEXT 32K))
    COMPRESS FOR OLTP;

CREATE TABLE purchaseorder_as_column (
  id NUMBER,
  xml_document XMLType,
  UNIQUE (xml_document."XMLDATA"."Reference"),
  FOREIGN KEY (xml_document."XMLDATA"."User") REFERENCES hr.employees (email))
  XMLTYPE COLUMN xml_document
  XMLSCHEMA "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd"
  ELEMENT "PurchaseOrder"
  VARRAY xml_document."XMLDATA"."LineItems"."LineItem" STORE AS LOB lineitem_lob
  LOB (xml_document."XMLDATA"."Notes")
    STORE AS (TABLESPACE USERS ENABLE STORAGE IN ROW 
              STORAGE(INITIAL 4K NEXT 32K))
    COMPRESS FOR OLTP;

CREATE TABLE purchaseorder_as_table OF XMLType (UNIQUE ("XMLDATA"."Reference"),
  FOREIGN KEY ("XMLDATA"."User") REFERENCES hr.employees (email))
  ELEMENT
    "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd#PurchaseOrder"
  STORE ALL VARRAYS AS LOBS;

Specifying Relational Constraints on XMLType Tables and Columns

When you store XML data using structured storage, typical relational constraints can be specified for elements and attributes that occur only once in an XML document. Example 7-22 shows how to use object-relational notation to define a unique constraint and a foreign key constraint when creating the table.

It is not possible to define constraints for XMLType tables and columns that make use of unstructured storage.

Common Uses of XML Schema Annotations

Common reasons for wanting to annotate an XML schema include the following:

• To ensure that the names of the tables, objects, and object attributes created by PL/SQL procedure DBMS_XMLSCHEMA.registerSchema for structured storage of XML data are easy to recognize and compliant with any application-naming standards. Set parameter GENTYPES or GENTABLES to TRUE for this.

• To map between the XML schema and existing objects and tables within the database. Set parameter GENTYPES or GENTABLES to FALSE for this.

• To prevent the generation of mixed-case names that require the use of quoted identifiers when working directly with SQL.

• To allow XPath rewrite for structured storage in the case of document-correlated recursive XPath queries. This applies to certain applications of SQL/XML access and query functions whose XQuery-expression argument targets recursive XML data.

The most commonly used XML schema annotations are the following:

• xdb:defaultTable – Name of the default table generated for each global element when parameter GENTABLES is TRUE. Setting this to the empty string, "", prevents a default table from being generated for the element in question.

• xdb:SQLName – Name of the SQL object attribute that corresponds to each element or attribute defined in the XML schema.

• xdb:SQLType – For complexType definitions, the corresponding object type. For simpleType definitions, SQLType is used to override the default mapping between XML schema data types and SQL data types. A common use of SQLType is to define when unbounded strings should be stored as CLOB values, rather than as VARCHAR(4000) CHAR values (the default). Note: You cannot use data type NCHAR, NVARCHAR, or NCLOB as the value of a SQLType annotation.

• xdb:SQLCollType – Used to specify the varray type that manages a collection of elements.

• xdb:maintainDOM – Used to determine whether or not DOM fidelity should be maintained for a given complexType definition

• xdb:storeVarrayAsTable – Specified in the root element of the XML schema. Used to force all collections to be stored as ordered collection tables (OCTs). An OCT is created for each element that is specified with maxOccurs > 1. The OCTs are created with system-generated names. The default value of storeVarrayAsTable is true.

You need not specify values for any of these attributes. Oracle XML DB provides appropriate values by default during the XML schema registration process. However, if you are using structured storage, then Oracle recommends that you specify the names of at least the top-level SQL types, so that you can reference them later.

XML Schema Annotation Example

Example 7-24 shows a partial listing of the XML schema in Example 7-1, modified to include some of the most important Oracle XML DB annotations.

<xs:schema
  targetNamespace="http://xmlns.oracle.com/xdb/documentation/purchaseOrder"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:xdb="http://xmlns.oracle.com/xdb"
  xmlns:po="http://xmlns.oracle.com/xdb/documentation/purchaseOrder"
  version="1.0" 
  xdb:storeVarrayAsTable="true">  <xs:element name="PurchaseOrder" type="po:PurchaseOrderType"
              xdb:defaultTable="PURCHASEORDER"/>
  <xs:complexType name="PurchaseOrderType" xdb:SQLType="PURCHASEORDER_T">
    <xs:sequence>
      <xs:element name="Reference" type="po:ReferenceType" minOccurs="1"
                  xdb:SQLName="REFERENCE"/>
      <xs:element name="Actions" type="po:ActionsType"
                  xdb:SQLName="ACTION_COLLECTION"/>
      <xs:element name="Reject" type="po:RejectionType" minOccurs="0"/>
      <xs:element name="Requestor" type="po:RequestorType"/>
      <xs:element name="User" type="po:UserType" minOccurs="1"
                  xdb:SQLName="EMAIL"/>
      <xs:element name="CostCenter" type="po:CostCenterType"/>
      <xs:element name="ShippingInstructions"
                  type="po:ShippingInstructionsType"/>
      <xs:element name="SpecialInstructions" type="po:SpecialInstructionsType"/>
      <xs:element name="LineItems" type="po:LineItemsType"
                  xdb:SQLName="LINEITEM_COLLECTION"/>
      <xs:element name="Notes" type="po:NotesType" xdb:SQLType="CLOB"/>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="LineItemsType" xdb:SQLType="LINEITEMS_T">
    <xs:sequence>
      <xs:element name="LineItem" type="po:LineItemType" maxOccurs="unbounded"
                  xdb:SQLCollType="LINEITEM_V" xdb:SQLName="LINEITEM_VARRAY"/>
   </xs:sequence>
  </xs:complexType>
  <xs:complexType name="LineItemType" xdb:SQLType="LINEITEM_T">
    <xs:sequence>
      <xs:element name="Description" type="po:DescriptionType"/>
      <xs:element name="Part" type="po:PartType"/>
    </xs:sequence>
    <xs:attribute name="ItemNumber" type="xs:integer"/>
  </xs:complexType>
  <xs:complexType name="PartType" xdb:SQLType="PART_T" xdb:maintainDOM="false">
    <xs:attribute name="Id">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:minLength value="10"/>
          <xs:maxLength value="14"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:attribute>
    <xs:attribute name="Quantity" type="po:moneyType"/>
    <xs:attribute name="UnitPrice" type="po:quantityType"/>
  </xs:complexType>
</xs:schema>

The schema element includes the declaration of the xdb namespace. It also includes the annotation xdb:storeVarrayAsTable = "true" (which is the default value). This causes all collections within the XML schema to be managed using ordered collection tables (OCTs).

The definition of global element PurchaseOrder includes a defaultTable annotation that specifies that the name of the default table associated with this element is purchaseorder.

The definition of global complex type PurchaseOrderType includes a SQLType annotation that specifies that the generated SQL object type is named purchaseorder_t. Within the definition of this type, the following annotations are used:

• The definition of element Reference includes a SQLName annotation that specifies that the SQL attribute corresponding to XML element Reference is named reference.

• The definition of element Actions includes a SQLName annotation that specifies that the SQL attribute corresponding to XML element Actions is named action_collection.

• The definition of element USER includes a SQLName annotation that specifies that the SQL attribute corresponding to XML element User is named email.

• The definition of element LineItems includes a SQLName annotation that specifies that the SQL attribute corresponding to XML element LineItems is named lineitem_collection.

• The definition of element Notes includes a SQLType annotation that specifies that the data type of the SQL attribute corresponding to XML element Notes is CLOB.

The definition of global complex type LineItemsType includes a SQLType annotation that specifies that the generated SQL object type is named lineitems_t. Within the definition of this type, the following annotations are used:

• The definition of element LineItem includes a SQLName annotation that specifies that the data type of the SQL attribute corresponding to XML element LineItems is named lineitem_varray, and a SQLCollName annotation that specifies that the SQL object type that manages the collection is named lineitem_v.

The definition of global complex type LineItemType includes a SQLType annotation that specifies that generated SQL object type is named lineitem_t.

The definition of complex type PartType includes a SQLType annotation that specifies that the SQL object type is named part_t. It also includes the annotation xdb:maintainDOM = "false", specifying that there is no need for Oracle XML DB to maintain DOM fidelity for elements based on this data type.

Example 7-25 shows some of the tables and objects that are created when the annotated XML schema is registered.

BEGIN
  DBMS_XMLSCHEMA.registerSchema(
    SCHEMAURL => 'http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd',
    SCHEMADOC => bfilename('XMLDIR', 'purchaseOrder.Annotated.xsd'),
    LOCAL     => TRUE,
    GENTYPES  => TRUE,
    GENTABLES => TRUE,
    CSID      => nls_charset_id('AL32UTF8'));
END;
/
 
SELECT table_name, xmlschema, element_name FROM USER_XML_TABLES;
 
TABLE_NAME     XMLSCHEMA                             ELEMENT_NAME
-------------  -----------------------------------   -------------
PURCHASEORDER  http://xmlns.oracle.com/xdb/documen   PurchaseOrder
               tation/purchaseOrder.xsd              
 
1 row selected.
 
DESCRIBE purchaseorder

Name                            Null? Type
------------------------------  ----- -----------------
TABLE of SYS.XMLTYPE(XMLSchema
 "http://xmlns.oracle.com/xdb/documentation/purchaseOrder.xsd"
 ELEMENT "PurchaseOrder") STORAGE Object-relational TYPE "PURCHASEORDER_T"
 
DESCRIBE purchaseorder_t

PURCHASEORDER_T is NOT FINAL
Name                 Null? Type
-------------------- ----- --------------------------
SYS_XDBPD$                 XDB.XDB$RAW_LIST_T
REFERENCE                  VARCHAR2(30 CHAR)
ACTION_COLLECTION          ACTIONS_T
REJECT                     REJECTION_T
REQUESTOR                  VARCHAR2(128 CHAR)
EMAIL                      VARCHAR2(10 CHAR)
COSTCENTER                 VARCHAR2(4 CHAR)
SHIPPINGINSTRUCTIONS       SHIPPING_INSTRUCTIONS_T
SPECIALINSTRUCTIONS        VARCHAR2(2048 CHAR)
LINEITEM_COLLECTION        LINEITEMS_T
Notes                      CLOB

DESCRIBE lineitems_t
LINEITEMS_T is NOT FINAL
Name                 Null? Type
-------------------- ----- --------------------------
SYS_XDBPD$                 XDB.XDB$RAW_LIST_T
LINEITEM_VARRAY            LINEITEM_V

DESCRIBE lineitem_v

LINEITEM_V VARRAY(2147483647) OF LINEITEM_T
LINEITEM_T is NOT FINAL
Name                 Null? Type
-------------------- ----- --------------------------
SYS_XDBPD$                 XDB.XDB$RAW_LIST_T
ITEMNUMBER                 NUMBER(38)
DESCRIPTION                VARCHAR2(256 CHAR)
PART                       PART_T

DESCRIBE part_t
 
PART_T is NOT FINAL
Name                 Null? Type
-------------------- ----- --------------------------
ID                         VARCHAR2(14 CHAR)
QUANTITY                   NUMBER(12,2)
UNITPRICE                  NUMBER(8,4)

SELECT table_name, parent_table_column FROM USER_NESTED_TABLES
  WHERE parent_table_name = 'purchaseorder';

TABLE_NAME                       PARENT_TABLE_COLUMN
----------                       -----------------------   
SYS_NTNOHV+tfSTRaDTA9FETvBJw==   "XMLDATA"."LINEITEM_COLLECTION"."LINEITEM_VARRAY"
SYS_NTV4bNVqQ1S4WdCIvBK5qjZA==   "XMLDATA"."ACTION_COLLECTION"."ACTION_VARRAY"
 
2 rows selected.

The following are results of this XML schema registration:

• A table called purchaseorder was created.

• Types called purchaseorder_t, lineitems_t, lineitem_v, lineitem_t, and part_t were created. The attributes defined by these types are named according to supplied the SQLName annotations.

• The Notes attribute defined by purchaseorder_t is of data type CLOB.

• Type part_t does not include a positional descriptor (PD) attribute.

• Ordered collection tables (OCTs) were created to manage the collections of LineItem and Action elements.

Available Oracle XML DB XML Schema Annotations

Table 7-3, Table 7-4, and Table 7-5 list Oracle XML DB annotations that you can specify in element and attribute declarations. All annotations except those that have the prefix csx are applicable to XML schemas registered for structured storage. This includes the portions of hybrid storage that are stored object-relationally.

The following annotations apply to XML schemas that are registered for unstructured storage:

• xdb:defaultTable

• xdb:defaultTableSchema

The following annotations apply to XML schemas that are registered for binary XML storage:

• xdb:defaultTable

• xdb:defaultTableSchema

• xdb:tableProps

^Footnote 1 See "Mapping XML Schema Data Types to SQL Data Types".

^Footnote 1 See "Mapping XML Schema Data Types to SQL Data Types".

XML Schema Annotation Guidelines for Structured Storage

For XMLType data stored object-relationally (structured storage), careful planning is called for, to optimize performance. Similar considerations are in order as for ordinary relational data: the entity-relationship model, indexing, data types, table partitions, and so on.

To enable XPath rewrite and achieve optimal performance, you implement many such design choices using XML schema annotations. This section provides annotation guidelines to optimize the use of XMLType data stored object-relationally.

Example of Mapping XML Schema Data Types to SQL

Example 7-27 shows a simple example of mapping XML Schema data types to SQL data types. It uses attribute SQLType to specify the data-type mapping. It also uses attribute SQLName to specify the object attributes to use for various XML elements and attributes.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xdb="http://xmlns.oracle.com/xdb"
           version="1.0"
           xdb:storeVarrayAsTable="true">
  <xs:element name="PurchaseOrder" type="PurchaseOrderType" xdb:defaultTable="PURCHASEORDER"/>
  <xs:complexType name="PurchaseOrderType" xdb:SQLType="PURCHASEORDER_T">
    <xs:sequence>
      <xs:element name="Reference" type="ReferenceType" minOccurs="1" xdb:SQLName="REFERENCE"/>
      <xs:element name="Actions" type="ActionsType" xdb:SQLName="ACTIONS"/>
      <xs:element name="Reject" type="RejectionType" minOccurs="0" xdb:SQLName="REJECTION"/>
      <xs:element name="Requestor" type="RequestorType" xdb:SQLName="REQUESTOR"/>
      <xs:element name="User" type="UserType" minOccurs="1" xdb:SQLName="USERID"/>
      <xs:element name="CostCenter" type="CostCenterType" xdb:SQLName="COST_CENTER"/>
      <xs:element name="ShippingInstructions" type="ShippingInstructionsType" 
                  xdb:SQLName="SHIPPING_INSTRUCTIONS"/>
      <xs:element name="SpecialInstructions" type="SpecialInstructionsType" 
                  xdb:SQLName="SPECIAL_INSTRUCTIONS"/>
      <xs:element name="LineItems" type="LineItemsType" xdb:SQLName="LINEITEMS"/>
      <xs:element name="Notes" type="po:NotesType" xdb:SQLType="CLOB"/>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="LineItemsType" xdb:SQLType="LINEITEMS_T">
    <xs:sequence>
      <xs:element name="LineItem" type="LineItemType" maxOccurs="unbounded" 
                  xdb:SQLName="LINEITEM" xdb:SQLCollType="LINEITEM_V"/>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="LineItemType" xdb:SQLType="LINEITEM_T">
    <xs:sequence>
      <xs:element name="Description" type="DescriptionType" 
                  xdb:SQLName="DESCRIPTION"/>
      <xs:element name="Part" type="PartType" xdb:SQLName="PART"/>
    </xs:sequence>
    <xs:attribute name="ItemNumber" type="xs:integer" xdb:SQLName="ITEMNUMBER" 
                  xdb:SQLType="NUMBER"/>
  </xs:complexType>
  <xs:complexType name="PartType" xdb:SQLType="PART_T">
    <xs:attribute name="Id" xdb:SQLName="PART_NUMBER" xdb:SQLType="VARCHAR2">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:minLength value="10"/>
          <xs:maxLength value="14"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:attribute>
    <xs:attribute name="Quantity" type="moneyType" xdb:SQLName="QUANTITY"/>
    <xs:attribute name="UnitPrice" type="quantityType" xdb:SQLName="UNITPRICE"/>
  </xs:complexType>

  ...

  <xs:complexType name="ActionsType" xdb:SQLType="ACTIONS_T">
    <xs:sequence>
      <xs:element name="Action" maxOccurs="4" xdb:SQLName="ACTION" xdb:SQLCollType="ACTION_V">
        <xs:complexType xdb:SQLType="ACTION_T">
          <xs:sequence>
            <xs:element name="User" type="UserType" xdb:SQLName="ACTIONED_BY"/>
            <xs:element name="Date" type="DateType" minOccurs="0" xdb:SQLName="DATE_ACTIONED"/>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="RejectionType" xdb:SQLType="REJECTION_T">
    <xs:all>
      <xs:element name="User" type="UserType" minOccurs="0" xdb:SQLName="REJECTED_BY"/>
      <xs:element name="Date" type="DateType" minOccurs="0" xdb:SQLName="DATE_REJECTED"/>
      <xs:element name="Comments" type="CommentsType" minOccurs="0" xdb:SQLName="REASON_REJECTED"/>
    </xs:all>
  </xs:complexType>
  <xs:complexType name="ShippingInstructionsType" xdb:SQLType="SHIPPING_INSTRUCTIONS_T">
    <xs:sequence>
      <xs:element name="name" type="NameType" minOccurs="0" xdb:SQLName="SHIP_TO_NAME"/>
      <xs:element name="address" type="AddressType" minOccurs="0" xdb:SQLName="SHIP_TO_ADDRESS"/>
      <xs:element name="telephone" type="TelephoneType" minOccurs="0" xdb:SQLName="SHIP_TO_PHONE"/>
    </xs:sequence>
  </xs:complexType>
  ...
</xs:schema>

Mapping XML Schema Attribute Data Types to SQL

An attribute declaration can specify its XML Schema data type in terms of one of the following:

• Primitive type

• Global simpleType, declared within this XML schema or in an external XML schema

• Reference to global attribute (ref=".."), declared within this XML schema or in an external XML schema

• Local simpleType

In all cases, the SQL data type, its associated information (length, precision), and the memory mapping information are derived from the simpleType on which the attribute is based.

Mapping XML Schema Element Data Types to SQL

An element declaration can specify its XML Schema data type in terms of one of the following:

• Any of the ways for specifying type for an attribute declaration. See "Mapping XML Schema Attribute Data Types to SQL" .

• Global complexType, specified within this XML schema document or in an external XML schema.

• Reference to a global element (ref="..."), which could itself be within this XML schema document or in an external XML schema.

• Local complexType.

Mapping simpleType to SQL

This section describes how XML schema definitions map XML Schema simpleType to SQL object types. Figure 7-6 shows an example of this.

Figure 7-6 Mapping simpleType: XML Strings to SQL VARCHAR2 or CLOB

Description of "Figure 7-6 Mapping simpleType: XML Strings to SQL VARCHAR2 or CLOB"

Table 7-6 through Table 7-9 present the default mapping of XML Schema simpleType to SQL, as specified in the XML Schema definition. For example:

• A XML Schema primitive type is mapped to the closest SQL data type. For example, DECIMAL, POSITIVEINTEGER, and FLOAT are all mapped to SQL NUMBER.

• An XML Schema enumeration type is mapped to a SQL object type with a single RAW(n) object attribute. The value of n is determined by the number of possible values in the enumeration declaration.

• An XML Schema list or a union type is mapped to a SQL string (VARCHAR2 or CLOB) data type.

<element name="dob" type="xsd:dateTime"
          xdb:SQLType="TIMESTAMP WITH TIME ZONE"/>
<attribute name="endofquarter" type="xsd:gMonthDay"
           xdb:SQLType="TIMESTAMP WITH TIME ZONE"/>

Mapping complexType to SQL

Using XML Schema, a complexType is mapped to a SQL object type as follows:

• XML attributes declared within the complexType are mapped to SQL object attributes. The simpleType defining an XML attribute determines the SQL data type of the corresponding object attribute.

• XML elements declared within the complexType are also mapped to SQL object attributes. The simpleType or complexType defining an XML element determines the SQL data type of the corresponding object attribute.

If the XML element is declared with attribute maxOccurs > 1, then it is mapped to a SQL collection (object) attribute. The collection could be a varray value (the default, recommended) or an unordered table (if you set attribute xdb:maintainOrder to false). The default storage of a varray value is an ordered collections table (OCT). You can choose LOB storage instead, by setting attribute xdb:storeVarrayAsTable to false.

<xs:complexType name="LineItemsType" xdb:SQLType="LINEITEMS_T">
    <xs:sequence>
      <xs:element name="LineItem" type="LineItemType" maxOccurs="unbounded" 
                  xdb:SQLName="LINEITEM" xdb:SQLCollType="LINEITEM_V"/>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="LineItemType" xdb:SQLType="LINEITEM_T">
    <xs:sequence>
      <xs:element name="Description" type="DescriptionType" 
                  xdb:SQLName="DESCRIPTION"/>
      <xs:element name="Part" type="PartType" xdb:SQLName="PART"/>
    </xs:sequence>
    <xs:attribute name="ItemNumber" type="xs:integer" xdb:SQLName="ITEMNUMBER" 
                  xdb:SQLType="NUMBER"/>
  </xs:complexType>
  <xs:complexType name="PartType" xdb:SQLType="PART_T">
    <xs:attribute name="Id" xdb:SQLName="PART_NUMBER" xdb:SQLType="VARCHAR2">
      <xs:simpleType>
        <xs:restriction base="xs:string">
          <xs:minLength value="10"/>
          <xs:maxLength value="14"/>
        </xs:restriction>
      </xs:simpleType>
    </xs:attribute>
    <xs:attribute name="Quantity" type="moneyType" xdb:SQLName="QUANTITY"/>
    <xs:attribute name="UnitPrice" type="quantityType" xdb:SQLName="UNITPRICE"/>
  </xs:complexType>