10 XML Schema Evolution

Scenario for Copy-Based Evolution

Example 10-1 shows a partial listing of a revised version of the purchase-order XML schema of Example 3-10. See Example A-2 for the complete revised schema listing. Text that is in bold here is new or different from that in the original schema.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xdb="http://xmlns.oracle.com/xdb"
           version="1.0">
  <xs:element
    name="PurchaseOrder" type="PurchaseOrderType"
    xdb:defaultTable="PURCHASEORDER"
    xdb:columnProps=
      "CONSTRAINT purchaseorder_pkey PRIMARY KEY (XMLDATA.reference),
       CONSTRAINT valid_email_address FOREIGN KEY (XMLDATA.userid)
         REFERENCES hr.employees (EMAIL)"
    xdb:tableProps=
      "VARRAY XMLDATA.ACTIONS.ACTION STORE AS TABLE ACTION_TABLE
        ((CONSTRAINT action_pkey PRIMARY KEY (NESTED_TABLE_ID, SYS_NC_ARRAY_INDEX$)))
       VARRAY XMLDATA.LINEITEMS.LINEITEM STORE AS TABLE LINEITEM_TABLE
        ((constraint LINEITEM_PKEY primary key (NESTED_TABLE_ID, SYS_NC_ARRAY_INDEX$)))
       lob (XMLDATA.NOTES) STORE AS (ENABLE STORAGE IN ROW STORAGE(INITIAL 4K NEXT 32K))"/>
  <xs:complexType name="PurchaseOrderType" xdb:SQLType="PURCHASEORDER_T">
    <xs:sequence>
      <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" xdb:SQLName="USERID"/>
      <xs:element name="CostCenter" type="CostCenterType" xdb:SQLName="COST_CENTER"/> 
      <xs:element name="BillingAddress" type="AddressType" minOccurs="0"
                  xdb:SQLName="BILLING_ADDRESS"/> 
      <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="NotesType" minOccurs="0" xdb:SQLType="CLOB"
                  xdb:SQLName="NOTES"/> 
    </xs:sequence>
    <xs:attribute name="Reference" type="ReferenceType" use="required" xdb:SQLName="REFERENCE"/>
    <xs:attribute name="DateCreated" type="xs:dateTime" use="required"
                  xdb:SQLType="TIMESTAMP WITH TIME ZONE"/>
  </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="Part" type="PartType" xdb:SQLName="PART"/>
      <xs:element name="Quantity" type="quantityType"/>
    </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:simpleContent>
      <xs:extension base="UPCCodeType">
        <xs:attribute name="Description" type="DescriptionType" use="required"
                      xdb:SQLName="DESCRIPTION"/> 
        <xs:attribute name="UnitCost" type="moneyType" use="required"/>
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
  <xs:simpleType name="ReferenceType">
    <xs:restriction base="xs:string">
      <xs:minLength value="18"/>
      <xs:maxLength value="30"/>
    </xs:restriction>
  </xs:simpleType>

. . .

  <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:choice>
        <xs:element name="address" type="AddressType" minOccurs="0"/>
        <xs:element name="fullAddress" type="FullAddressType" minOccurs="0"
                    xdb:SQLName="SHIP_TO_ADDRESS"/> 
      </xs:choice>
      <xs:element name="telephone" type="TelephoneType" minOccurs="0" xdb:SQLName="SHIP_TO_PHONE"/>
    </xs:sequence>
  </xs:complexType>

. . .

  <xs:simpleType name="NameType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="20"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="FullAddressType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="256"/>
    </xs:restriction>
  </xs:simpleType>

. . .

  <xs:simpleType name="DescriptionType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="256"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:complexType name="AddressType" xdb:SQLType="ADDRESS_T">
    <xs:sequence>
      <xs:element name="StreetLine1" type="StreetType"/>
      <xs:element name="StreetLine2" type="StreetType" minOccurs="0"/>
      <xs:element name="City" type="CityType"/>
      <xs:choice>
        <xs:sequence>
          <xs:element name="State" type="StateType"/>
          <xs:element name="ZipCode" type="ZipCodeType"/>
        </xs:sequence>
        <xs:sequence>
          <xs:element name="Province" type="ProvinceType"/>
          <xs:element name="PostCode" type="PostCodeType"/>
        </xs:sequence>
        <xs:sequence>
          <xs:element name="County" type="CountyType"/>
          <xs:element name="Postcode" type="PostCodeType"/>
        </xs:sequence>
      </xs:choice>
      <xs:element name="Country" type="CountryType"/>
    </xs:sequence>
  </xs:complexType>
  <xs:simpleType name="StreetType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="128"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="CityType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="64"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="StateType">
    <xs:restriction base="xs:string">
      <xs:minLength value="2"/>
      <xs:maxLength value="2"/>
      <xs:enumeration value="AK"/>
      <xs:enumeration value="AL"/>
      <xs:enumeration value="AR"/>

 . . . -- A value for each US state abbreviation

      <xs:enumeration value="WY"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="ZipCodeType">
    <xs:restriction base="xs:string">
      <xs:pattern value="\d{5}"/>
      <xs:pattern value="\d{5}-\d{4}"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="CountryType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="64"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="CountyType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="32"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="PostCodeType">
    <xs:restriction base="xs:string">
      <xs:minLength value="1"/>
      <xs:maxLength value="12"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="ProvinceType">
    <xs:restriction base="xs:string">
      <xs:minLength value="2"/>
      <xs:maxLength value="2"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="NotesType">
    <xs:restriction base="xs:string">
      <xs:maxLength value="32767"/>
    </xs:restriction>
  </xs:simpleType>
  <xs:simpleType name="UPCCodeType">
    <xs:restriction base="xs:string">
      <xs:minLength value="11"/>
      <xs:maxLength value="14"/>
      <xs:pattern value="\d{11}"/>
      <xs:pattern value="\d{12}"/>
      <xs:pattern value="\d{13}"/>
      <xs:pattern value="\d{14}"/>
    </xs:restriction>
  </xs:simpleType>
</xs:schema>

copyEvolve Parameters and Errors

This is the signature of procedure DBMS_XMLSCHEMA.copyEvolve:

procedure copyEvolve(schemaURLs       IN XDB$STRING_LIST_T,
                     newSchemas       IN XMLSequenceType,
                     transforms       IN XMLSequenceType := NULL,
                     preserveOldDocs  IN BOOLEAN := FALSE,
                     mapTabName       IN VARCHAR2 := NULL,
                     generateTables   IN BOOLEAN := TRUE,
                     force            IN BOOLEAN := FALSE,
                     schemaOwners     IN XDB$STRING_LIST_T := NULL
                     parallelDegree   IN PLS_INTEGER := 0,
                     options          IN PLS_INTEGER := 0);

Table 10-1 describes the individual parameters. Table 10-2 describes the errors associated with the procedure.

Limitations of Procedure COPYEVOLVE

Keep in mind the following limitations when you use procedure DBMS_XMLSCHEMA.copyEvolve:

• Indexes, triggers, constraints, row-level security (RLS) policies, and other metadata related to the XMLType tables that are dependent on the schemas are not preserved. These must be re-created after evolution.

• If top-level element names are changed, additional steps are required after copyEvolve finishes executing. See "Top-Level Element Name Changes".

• Copy-based evolution cannot be used if there is a table with an object-type column that has an XMLType attribute that is dependent on any of the schemas to be evolved. For example, consider this table:

  CREATE TYPE t1 AS OBJECT (n NUMBER, x XMLType);
  CREATE TABLE tab1 (e NUMBER, o t1) XMLType 
   COLUMN o.x XMLSchema "s1.xsd" ELEMENT "Employee";
  

  This assumes that an XML schema with a top-level element Employee has been registered under URL s1.xsd. It is not possible to evolve this XML schema, because table tab1 with column o with XMLType attribute x is dependent on the XML schema. Note that although copyEvolve does not handle XMLType object attributes, it does raise an error in such cases.

Guidelines for Using Procedure COPYEVOLVE

The following general guideline applies to using procedure DBMS_XMLSCHEMA.copyEvolve. The rest of this section describes specific guidelines that can also be appropriate in particular contexts.

1. Turn off the recycle bin, to prevent dropped tables from being copied to it:

   ALTER SESSION SET RECYCLEBIN=off;
   

2. Identify the XML schemas that are dependent on the XML schema that is to be evolved. You can acquire the URLs of the dependent XML schemas using the following query, where schema_to_be_evolved is the schema to be evolved, and owner_of_schema_to_be_evolved is its owner (database user).

   SELECT dxs.SCHEMA_URL, dxs.OWNER
       FROM DBA_DEPENDENCIES dd, DBA_XML_SCHEMAS dxs
       WHERE dd.REFERENCED_NAME = (SELECT INT_OBJNAME
                                     FROM DBA_XML_SCHEMAS
                                     WHERE SCHEMA_URL = schema_to_be_evolved
                                       AND OWNER = owner_of_schema_to_be_evolved)
         AND dxs.INT_OBJNAME = dd.NAME;
   

   In many cases, no changes are needed in the dependent XML schemas. But if the dependent XML schemas need to be changed, then you must also prepare new versions of those XML schemas.

3. If the existing instance documents do not conform to the new XML schema, then you must provide an XSL style sheet that, when applied to an instance document, transforms it to conform to the new schema. You must do this for each XML schema identified in Step 2. The transformation must handle documents that conform to all top-level elements in the new XML schema.

4. Call procedure DBMS_XMLSCHEMA.copyEvolve, specifying the XML schema URLs, new schemas, and transformation style sheet.

SELECT TABLE_NAME FROM USER_TABLES WHERE TABLE_NAME LIKE 'XDB$MAPTAB%';

Updating Existing XML Instance Documents using a Style Sheet

After you modify a registered XML schema, you must update any existing XML instance documents that use the XML schema. You do this by applying an XSLT style sheet to each of the instance documents. The style sheet represents the difference between the old and new XML schemas.

Example 10-2 is a style sheet, in file evolvePurchaseOrder.xsl, that transforms existing purchase-order documents that use the old XML schema, so they use the new XML schema instead.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet 
  version="1.0" 
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <xsl:output method="xml" encoding="UTF-8"/>
  <xsl:template match="/PurchaseOrder">
    <PurchaseOrder>
      <xsl:attribute name="xsi:noNamespaceSchemaLocation">
        http://localhost:8080/source/schemas/poSource/xsd/purchaseOrder.xsd
      </xsl:attribute>
      <xsl:for-each select="Reference">
        <xsl:attribute name="Reference">
          <xsl:value-of select="."/>
        </xsl:attribute>
      </xsl:for-each>
      <xsl:variable name="V264_394" select="'2004-01-01T12:00:00.000000-08:00'"/>
      <xsl:attribute name="DateCreated">
        <xsl:value-of select="$V264_394"/>
      </xsl:attribute>
      <xsl:for-each select="Actions">
        <Actions>
          <xsl:for-each select="Action">
            <Action>
              <xsl:for-each select="User">
                <User>
                  <xsl:value-of select="."/>
                </User>
              </xsl:for-each>
              <xsl:for-each select="Date">
                <Date>
                  <xsl:value-of select="."/>
                </Date>
              </xsl:for-each>
            </Action>
          </xsl:for-each>
        </Actions>
      </xsl:for-each>
      <xsl:for-each select="Reject">
        <Reject>
          <xsl:for-each select="User">
            <User>
              <xsl:value-of select="."/>
            </User>
          </xsl:for-each>
          <xsl:for-each select="Date">
            <Date>
              <xsl:value-of select="."/>
            </Date>
          </xsl:for-each>
          <xsl:for-each select="Comments">
            <Comments>
              <xsl:value-of select="."/>
            </Comments>
          </xsl:for-each>
        </Reject>
      </xsl:for-each>
      <xsl:for-each select="Requestor">
        <Requestor>
          <xsl:value-of select="."/>
        </Requestor>
      </xsl:for-each>
      <xsl:for-each select="User">
        <User>
          <xsl:value-of select="."/>
        </User>
      </xsl:for-each>
      <xsl:for-each select="CostCenter">
        <CostCenter>
          <xsl:value-of select="."/>
        </CostCenter>
      </xsl:for-each>
      <ShippingInstructions>
        <xsl:for-each select="ShippingInstructions">
          <xsl:for-each select="name">
            <name>
              <xsl:value-of select="."/>
            </name>
          </xsl:for-each>
        </xsl:for-each>
        <xsl:for-each select="ShippingInstructions">
          <xsl:for-each select="address">
            <fullAddress>
              <xsl:value-of select="."/>
            </fullAddress>
          </xsl:for-each>
        </xsl:for-each>
        <xsl:for-each select="ShippingInstructions">
          <xsl:for-each select="telephone">
            <telephone>
              <xsl:value-of select="."/>
            </telephone>
          </xsl:for-each>
        </xsl:for-each>
      </ShippingInstructions>
      <xsl:for-each select="SpecialInstructions">
        <SpecialInstructions>
          <xsl:value-of select="."/>
        </SpecialInstructions>
      </xsl:for-each>
      <xsl:for-each select="LineItems">
        <LineItems>
          <xsl:for-each select="LineItem">
            <xsl:variable name="V22" select="."/>
            <LineItem>
              <xsl:for-each select="@ItemNumber">
                <xsl:attribute name="ItemNumber">
                  <xsl:value-of select="."/>
                </xsl:attribute>
              </xsl:for-each>
              <xsl:for-each select="$V22/Part">
                <xsl:variable name="V24" select="."/>
                <xsl:for-each select="@Id">
                  <Part>
                    <xsl:for-each select="$V22/Description">
                      <xsl:attribute name="Description">
                        <xsl:value-of select="."/>
                      </xsl:attribute>
                    </xsl:for-each>
                    <xsl:for-each select="$V24/@UnitPrice">
                      <xsl:attribute name="UnitCost">
                        <xsl:value-of select="."/>
                      </xsl:attribute>
                    </xsl:for-each>
                    <xsl:value-of select="."/>
                  </Part>
                </xsl:for-each>
              </xsl:for-each>
              <xsl:for-each select="$V22/Part">
                <xsl:for-each select="@Quantity">
                  <Quantity>
                    <xsl:value-of select="."/>
                  </Quantity>
                </xsl:for-each>
              </xsl:for-each>
            </LineItem>
          </xsl:for-each>
        </LineItems>
      </xsl:for-each>
    </PurchaseOrder>
  </xsl:template>
</xsl:stylesheet>

Examples of Using Procedure COPYEVOLVE

Example 10-3 loads a revised XML schema and evolution XSL style sheet into Oracle XML DB Repository.

DECLARE
  res BOOLEAN;
BEGIN
  res := DBMS_XDB.createResource(               -- Load revised XML schema
           '/source/schemas/poSource/revisedPurchaseOrder.xsd',
           bfilename('XMLDIR', 'revisedPurchaseOrder.xsd'),
           nls_charset_id('AL32UTF8'));
  res := DBMS_XDB.createResource(               -- Load revised XSL style sheet
           '/source/schemas/poSource/evolvePurchaseOrder.xsl',
           bfilename('XMLDIR', 'evolvePurchaseOrder.xsl'),
           nls_charset_id('AL32UTF8'));
END;/

Example 10-4 shows how to use procedure DBMS_XMLSCHEMA.copyEvolve to evolve the XML schema purchaseOrder.xsd to revisedPurchaseOrder.xsd using the XSL style sheet evolvePurchaseOrder.xsl.

BEGIN
  DBMS_XMLSCHEMA.copyEvolve(
    xdb$string_list_t('http://localhost:8080/source/schemas/poSource/xsd/purchaseOrder.xsd'),
    XMLSequenceType(XDBURIType('/source/schemas/poSource/revisedPurchaseOrder.xsd').getXML()),
    XMLSequenceType(XDBURIType('/source/schemas/poSource/evolvePurchaseOrder.xsl').getXML()));
END;

SELECT XMLQuery('$p/PurchaseOrder/LineItems/LineItem[1]'
                PASSING po.OBJECT_VALUE AS "p" RETURNING CONTENT) line_item
  FROM purchaseorder po
  WHERE XMLExists('$p/PurchaseOrder[Reference="SBELL-2003030912333601PDT"]'
                  PASSING po.OBJECT_VALUE AS "p");
 
LINE_ITEM
------------------------------------------------------------------------------
<LineItem ItemNumber="1">
  <Part Description="A Night to Remember" UnitCost="39.95">715515009058</Part>
  <Quantity>2</Quantity>
</LineItem>

LINE_ITEM
----------------------------------------------------------
<LineItem ItemNumber="1">
  <Description>A Night to Remember</Description>
  <Part Id="715515009058" UnitPrice="39.95" Quantity="2"/>
</LineItem>

Procedure DBMS_XMLSCHEMA.copyEvolve evolves registered XML schemas in such a way that existing instance documents continue to remain valid.

First, procedure copyEvolve copies the data in XML schema-based XMLType tables and columns to temporary tables. It then drops the original tables and columns, and deletes the old XML schemas. After registering the new XML schemas, it creates XMLType tables and columns and populates them with data (unless parameter GENTABLES is FALSE) but it does not create any auxiliary structures such as indexes, constraints, triggers, and row-level security (RLS) policies. Procedure copyEvolve creates the tables and columns as follows:

• It creates default tables while registering the new schemas.

• It creates tables that are not default tables using a statement of the following form:

  CREATE TABLE table_name OF XMLType OID 'oid'   XMLSCHEMA schema_url ELEMENT element_name
  

  where OID is the original OID of the table, before it was dropped.

• It adds XMLType columns using a statement of the following form:

  ALTER TABLE table_name ADD (column_name XMLType) XMLType COLUMN
   column_name XMLSCHEMA schema_url ELEMENT element_name
  

When a new XML schema is registered, types are generated if the registration of the corresponding old schema had generated types. If an XML schema was global before the evolution, then it is also global after the evolution. Similarly, if an XML schema was local before the evolution, then it is also local (owned by the same user) after the evolution.You have the option to preserve the temporary tables that contain the old documents, by setting parameter preserveOldDocs to TRUE. All temporary tables are created in the database schema of the current user. For XMLType tables, the temporary table has the columns shown in Table 10-3.

For XMLType columns, the temporary table has the columns shown in Table 10-4.

Procedure copyEvolve stores information about the mapping from the old table or column name to the corresponding temporary table name in a separate table specified by parameter mapTabName. If preserveOldDocs is TRUE, then the mapTabName parameter must not be NULL, and it must not be the name of any existing table in the current database schema. Each row in the mapping table has information about one of the old tables/columns. Table 10-5 shows the mapping table columns.

You can avoid generating any tables or columns after registering the new XML schema by setting parameter GENTABLES to FALSE. If GENTABLES is FALSE, parameter PRESERVEOLDDOCS must be TRUE and parameter MAPTABNAME must not be NULL. This ensures that the data in the old tables is not lost. This is useful if you do not want the tables to be created by the procedure, as described in section "copyEvolve Parameters and Errors".

By default, it is assumed that all XML schemas are owned by the current user. If this is not true, then you must specify the owner of each XML schema in the schemaOwners parameter.

Restrictions for In-Place XML Schema Evolution

Because in-place XML schema evolution avoids copying data, it does not permit arbitrary changes to an XML schema. This section describes why certain changes are not permitted. For the list of changes supported by in-place evolution, see "Supported Operations for In-Place XML Schema Evolution".

The primary restriction on using in-place evolution can be stated generally as a requirement that a given XML schema can be evolved in place in only a backward-compatible way. Backward-compatible here means that any possible instance document that would validate against a given XML schema must also validate against a later (evolved) version of that XML schema.

This applies to all possible conforming instance documents, not only to existing instance documents For XML data that is stored as binary XML, backward compatibility also means that any XML schema annotations that affect binary XML treatment must not change during evolution. Backward compatibility is described in section "Backward-Compatibility Restrictions".

In addition to this general backward-compatibility restriction, there are some other restrictions for in-place evolution. These are described in section "Other Restrictions on In-Place Evolution".

<complexType name="ShippingInstructionsType"> 
    <sequence> 
        <element name="name"   type="NameType" minOccurs="0"/> 
        <element name="address" type="AddressType" minOccurs="0"/> 
        <element name="telephone" type="TelephoneType" minOccurs="0"/> 
    </sequence> 
</complexType> 
 
<complexType name="Person-Name"> 
    <sequence> 
        <element name="name" type="NameType" minOccurs="0"/> 
    </sequence>
</complexType>
 
<complexType name="Contact-Info">
    <sequence>
        <element name="address" type="AddressType" minOccurs="0"/> 
        <element name="telephone" type="TelephoneType" minOccurs="0"/> 
    </sequence> 
</complexType>

Supported Operations for In-Place XML Schema Evolution

This section describes operations that are supported for in-place schema evolution. This list of supported operations is not necessarily exhaustive. Some of the operations listed here are not permitted in specific contexts, which are specified. In particular, some of the operations described here are not permitted for XML schemas that are used with binary XML.

• Add an optional element to a complex type or group: Always permitted. An example is the addition of the optional element shipmethod in the following complex type definition:

  <xs:complexType name="ShippingInstructionsType">
      <xs:sequence>
          <xs:element name="name" type="NameType" minOccurs="0"/>
          <xs:element name="address" type="AddressType" minOccurs="0"/>
          <xs:element name="telephone" type="TelephoneType" minOccurs="0"/>
          <xs:element name = "shipmethod" type = "xs:string" minOccurs = "0"/>
      </xs:sequence>
  </xs:complexType>
  

• Add an optional attribute to a complex type or attribute group: Always permitted. An example is the addition of the optional attribute shipbydate in the following complex type definition:

  <xs:complexType name="ShippingInstructionsType">
      <xs:sequence>
          <xs:element name="name" type="NameType" minOccurs="0"/>
          <xs:element name="address" type="AddressType" minOccurs="0"/>
          <xs:element name="telephone" type="TelephoneType" minOccurs="0"/>
      </xs:sequence>
      <xs:attribute name="shipbydate" type="DateType" use="optional"/>
  </xs:complexType>
  

• Convert an element from simple type to complex type with simple content: Supported only if the storage model is binary XML.

• Modify the value attribute of an existing maxLength element: Always permitted. The value can only be increased, not decreased.

• Add an enumeration value: You can add a new enumeration value only to the end of an enumeration list.

• Add a global element: Always permitted. An example is the addition of the global element PurchaseOrderComment in the following schema definition:

  <xs:schema ...> 
  ... 
      <xs:element name="PurchaseOrderComment" type="string" xdb:defaultTable=""/> 
  .. 
  </xs:schema>
  

• Add a global attribute: Always permitted.

• Add or delete a global complex type: Always permitted. An example is the addition of the global complex type ComplexAddressType in the following schema definition:

  <xs:schema ...> 
  .... 
      <xs:complexType name="ComplexAddressType"> 
          <xs:sequence> 
              <xs:element name="street" type="string"/> 
              <xs:element name="city" type="string"/> 
              <xs:element ref="zip" type="positiveInteger"/> 
              <xs:element name="country"  type="string"/> 
          </xs:sequence> 
       </xs:complexType> 
  ... 
  </xs:schema>
  

• Add or delete a global simple type: Always permitted.

• Change the minOccurs attribute value: The value of minOccurs can only be decreased.

• Change the maxOccurs attribute value: The value of maxOccurs can only be increased, and this is only possible for data stored as binary XML. That is, you cannot make any change to the maxOccurs attribute for data stored object-relationally.

• Add or delete a global group or attributeGroup: Always permitted. An example is the addition of an Instructions group in the following type definition:

  <xsd:schema ...> 
  ... 
    <xsd:group name="Instructions"> 
      <xsd:sequence> 
       <xsd:element name="ShippingInstructions" type="ShippingInstructionsType"/> 
       <xsd:element name="SpecialInstructions" type=" SpecialInstructionsType"/> 
      </xsd:sequence> 
    </xsd:group> 
  ... 
  </xsd:schema>
  

• Change the xdb:defaultTable attribute value: Always permitted. Changes are not permitted to any other attributes in the xdb namespace.

• Add, modify, or delete a comment or processing instruction: Always permitted.

Guidelines for Using In-Place XML Schema Evolution

The following guidelines apply to in-place XML-schema evolution:

• Before you perform an in-place XML-schema evolution:

  • Back up all existing data (instance documents) for the XML schema to be evolved.

    Caution:

    Make sure that you back up your data before performing in-place XML schema evolution, in case the result is not what you intended. There is no rollback possible after an in-place evolution. If any errors occur during evolution, or if you make a major mistake and need to redo the entire operation, you must be able to go back to the backup copy of your original data.

  • Perform a dry run using trace only, that is, without actually evolving the XML schema or updating any instance documents, produce a trace of the update operations that would be performed during evolution. To do this, set the flag parameter value to only INPLACE_TRACE. Do not also use INPLACE_EVOLVE.

    After performing the dry run, examine the trace file, verifying that the listed DDL operations are in fact those that you intend.

• After you perform an in-place XML-schema evolution:

  If you are accessing the database using a client that caches data, or if you are not sure whether this is the case, then restart your client. Otherwise, the pre-evolution version of the XML schema might continue to be used locally, with unpredictable results.

inPlaceEvolve Parameters

This is the signature of procedure DBMS_XMLSCHEMA.inPlaceEvolve:

procedure inPlaceEvolve(schemaURL IN VARCHAR2,
                        diffXML   IN XMLType, 
                        flags     IN NUMBER);

Table 10-6 describes the individual parameters.

Procedure DBMS_XMLSCHEMA.inPlaceEvolve raises an error in the following cases:

• An XPath expression is invalid, or is syntactically correct but does not target a node in the XML schema.

• The diffXML document does not conform to the xdiff XML schema.

• The change makes the XML schema invalid or not well formed.

• A generated DDL statement (CREATE TYPE, ALTER TYPE, and so on) causes a problem when it is executed.

• An index object associated with an XMLType table is in an unsafe state, which could be caused by partition management operations.

Creating the Document for the diffXML Parameter

The value of the diffXML parameter to procedure DBMS_XMLSCHEMA.inPlaceEvolve is an XML document (as an XMLType instance) that specifies the changes to be applied to an XML schema for in-place evolution. This diffXML document contains a sequence of operations that describe the changes between the old XML schema and the new (the intended evolution result). The changes specified by the diffXML document are applied in order.

You must create the XML document to be used for the diffXML parameter You can do this in any of the following ways:

• The XMLDiff JavaBean (oracle.xml.differ.XMLDiff)

• The xmldiff command-line utility

• SQL function XMLDiff

The diffXML parameter document must conform to the xdiff XML schema.

The rest of this section presents examples of some operations in a document that conforms to the xdiff XML schema.

<xd:xdiff  xmlns="http://www.w3c.org/2001/XMLSchema" 
           xmlns:xd="http://xmlns.oracle.com/xdb/xdiff.xsd" 
           xmlns:xsi="http://www.w3c.org/2001/XMLSchema-Instance" 
           xsi:schemaLocation="http://xmlns.oracle.com/xdb/xdiff.xsd
           http://xmlns.oracle.com/xdb/xdiff.xsd"> 
 <xd:delete-node xpath="/schema/complexType[@name=&quote;PartType&quote;]//maxLength/> 
 <xd:append-node
  parent-xpath = "/schema/complexType[@name=&quote;PartType&quote;]//restriction"
  node-type = "element"> 
  <xd:content> 
    <xs:maxLength value = "28"/>
  </xd:content> 
 </xd:append-node> 
 <xd:insert-node-before 
  xpath="/schema/complexType[@name =&quote;ShippingInstructionsType&quote;]/sequence" 
  node-type="comment"> 
  <xd:content> 
    <!-- A type representing instructions for shipping --> 
  </xd:content> 
 </xd:insert-node-before> 
 <xd:append-node 
  parent-xpath="/schema/complexType[@name=&quote;ShippingInstructionsType&quote;]/sequence" 
  node-type="element"> 
  <xd:content> 
   <xs:element name = "shipmethod" type = "xs:string" minOccurs = "1"/> 
  </xd:content> 
 </xd:append-node> 
</xd:xdiff>