Handling substitution groups and Tables generation

Question

Hi
This is concerning the generation of tables from xml schema containing "substitutionGroup" attributes and "extension" elements for
deriving from abstract types.
I want to know how the tables are generated when schema has subsitution groups.
I went through the generated tables and observed that it creates a table for each extension...but also generates a table for the head of the subsitution group.
This table would have columns for each of the members in the derivatives of the abstract type.This is resulting in more than 1000 columns in my case
Any suggestions?
Thanks
Devashish

Answer 1

When a subsitution group is used each of the type of each of the elements in the substition group must be an extension of the type of the head element. In the case where the head type is based on an abstract empty complexType this makes no sense. Since the type inheritiance system implies that anywhere a parent type can appear it is legal for the chlild type to appear in it's place we have to create a storage structure for the head element which can handle any of the possible child types. This means that at the storage level we have to generate a table with a column for each possible descendant of the head element. This means that we are effectively restricting the number of direct elements and attributes that can be defined by members of the substition group to a number that is a little less than 1000.
This can be be seen in the first example below.
However in the case where the substition group contains no common element we can model this as choice. as is shown in the second XML Schema. Since every member of the choice is independant of the other members of the choice there is no need for the inheritance hierarchy in the type definitions. This means that each member of the choice can now be mapped to a seperate table. This structure allows for a choice with approxamately a 1000 entries and no practicle limits on the number of decendant elements and attributes for each member of the choice..
This can be seen in the second example bleow;
The key point is the number of columns in ROOT_TABLE. In the First Example it is 17, the fixed overhead plus the number of columns required to persist headType, member1Type and member2Type. In the Second example it is 12, the fixed overhead plus a REF XMLType to point at instances of member1Type and REF XMLType to point at instnaces of member2Type.
I hope this answers your question
SQL> var schemaURL varchar2(256)
SQL> var schemaPath varchar2(256)
SQL> --
SQL> column qualified_col_name format A64
SQL> column data_type format A40
SQL> --
SQL> set lines 150 pages 25 long 10000
SQL> --
SQL> begin
  2    :schemaURL := 'testcase.xsd';
  3    :schemaPath := '/public/testcase.xsd';
  4  end;
  5  /
PL/SQL procedure successfully completed.
SQL> call dbms_xmlSchema.deleteSchema(:schemaURL,4)
  2  /
Call completed.
SQL> declare
  2    res boolean;
  3    xmlSchema xmlType := xmlType(
  4  '<?xml version="1.0" encoding="UTF-8"?>
  5  <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xdb="http://xmlns.oracle.com/xdb" elementFormDefault="qualified" attribute
FormDefault="unqualified" xdb:storeVarrayAsTable="true">
  6     <xs:element name="root" type="rootType" xdb:defaultTable="ROOT_TABLE"/>
  7     <xs:complexType name="rootType" xdb:SQLType="ROOT_T">
  8             <xs:sequence>
  9                     <xs:element ref="head"/>
10             </xs:sequence>
11     </xs:complexType>
12     <xs:complexType name="headType" xdb:SQLType="HEAD_T" abstract="true"/>
13     <xs:complexType name="member1Type" xdb:SQLType="MEMBER1_T">
14             <xs:complexContent>
15                     <xs:extension base="headType">
16                             <xs:sequence>
17                                     <xs:element name="Member1.Child1" type="xs:string"/>
18                                     <xs:element name="Member1.Child2" type="xs:string"/>
19                             </xs:sequence>
20                     </xs:extension>
21             </xs:complexContent>
22     </xs:complexType>
23     <xs:complexType name="member2Type" xdb:SQLType="MEMBER2_T">
24             <xs:complexContent>
25                     <xs:extension base="headType">
26                             <xs:sequence>
27                                     <xs:element name="Member2.Child1" type="xs:string"/>
28                                     <xs:element name="Member2.Child2" type="xs:string"/>
29                             </xs:sequence>
30                     </xs:extension>
31             </xs:complexContent>
32     </xs:complexType>
33     <xs:element name="head" type="headType" xdb:defaultTable="GLOBAL_HEAD_TABLE"/>
34     <xs:element name="member1" type="member1Type" substitutionGroup="head" xdb:defaultTable="GLOBAL_MEMBER1_TABLE"/>
35     <xs:element name="member2" type="member2Type" substitutionGroup="head" xdb:defaultTable="GLOBAL_MEMBER2_TABLE"/>
36  </xs:schema>');
37  begin
38    if (dbms_xdb.existsResource(:schemaPath)) then
39      dbms_xdb.deleteResource(:schemaPath);
40    end if;
41    res := dbms_xdb.createResource(:schemaPath,xmlSchema);
42  end;
43  /
PL/SQL procedure successfully completed.
SQL> begin
  2    dbms_xmlschema.registerSchema
  3    (
  4      :schemaURL,
  5      xdbURIType(:schemaPath).getClob(),
  6      TRUE,TRUE,FALSE,TRUE
  7    );
  8  end;
  9  /
PL/SQL procedure successfully completed.
SQL> --
SQL> desc ROOT_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "root") STORAGE Object-relational TYPE "ROOT_T"
SQL> --
SQL> desc ROOT_T
ROOT_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
head                                                                                         HEAD_T
SQL> --
SQL> desc HEAD_T
HEAD_T is NOT FINAL
HEAD_T is NOT INSTANTIABLE
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
SQL> --
SQL> desc GLOBAL_HEAD_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "head") STORAGE Object-relational TYPE "HEAD_T"
SQL> --
SQL> desc GLOBAL_MEMBER1_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "member1") STORAGE Object-relational TYPE "MEMBER1_T"
SQL> --
SQL> desc MEMBER1_T
MEMBER1_T extends SCOTT.HEAD_T
MEMBER1_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
Member1.Child1                                                                               VARCHAR2(4000 CHAR)
Member1.Child2                                                                               VARCHAR2(4000 CHAR)
SQL> --
SQL> desc GLOBAL_MEMBER2_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "member2") STORAGE Object-relational TYPE "MEMBER2_T"
SQL> --
SQL> desc MEMBER2_T
MEMBER2_T extends SCOTT.HEAD_T
MEMBER2_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
Member2.Child1                                                                               VARCHAR2(4000 CHAR)
Member2.Child2                                                                               VARCHAR2(4000 CHAR)
SQL> --
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'ROOT_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          ROOT_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."head"                                                 HEAD_T
SYS_TYPEID("XMLDATA"."head")                                     RAW
"XMLDATA"."head"."SYS_XDBPD$"                                    XDB$RAW_LIST_T
TREAT("XMLDATA"."head" AS "MEMBER2_T")."Member2.Child1"          VARCHAR2
TREAT("XMLDATA"."head" AS "MEMBER2_T")."Member2.Child2"          VARCHAR2
TREAT("XMLDATA"."head" AS "MEMBER1_T")."Member1.Child1"          VARCHAR2
TREAT("XMLDATA"."head" AS "MEMBER1_T")."Member1.Child2"          VARCHAR2
ACLOID                                                           RAW
OWNERID                                                          RAW
17 rows selected.
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'GLOBAL_MEMBER1_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          MEMBER1_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."Member1.Child1"                                       VARCHAR2
"XMLDATA"."Member1.Child2"                                       VARCHAR2
ACLOID                                                           RAW
OWNERID                                                          RAW
12 rows selected.
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'GLOBAL_MEMBER2_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          MEMBER2_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."Member2.Child1"                                       VARCHAR2
"XMLDATA"."Member2.Child2"                                       VARCHAR2
ACLOID                                                           RAW
OWNERID                                                          RAW
12 rows selected.
SQL> insert into ROOT_TABLE values( XMLType (
  2  '<root>
  3    <member1>
  4      <Member1.Child1>AAA</Member1.Child1>
  5      <Member1.Child2>BBB</Member1.Child2>
  6    </member1>
  7  </root>'))
  8  /
1 row created.
SQL> insert into ROOT_TABLE values( XMLType (
  2  '<root>
  3    <member2>
  4      <Member2.Child1>CCC</Member2.Child1>
  5      <Member2.Child2>DDD</Member2.Child2>
  6    </member2>
  7  </root>'))
  8  /
1 row created.
SQL> set long 1000 pages 20
SQL> --
SQL> select * from ROOT_TABLE
  2  /
SYS_NC_ROWINFO$
<root>
  <member1>
    <Member1.Child1>AAA</Member1.Child1>
    <Member1.Child2>BBB</Member1.Child2>
  </member1>
</root>
<root>
  <member2>
    <Member2.Child1>CCC</Member2.Child1>
    <Member2.Child2>DDD</Member2.Child2>
  </member2>
</root>
SQL> var schemaURL varchar2(256)
SQL> var schemaPath varchar2(256)
SQL> --
SQL> begin
  2    :schemaURL := 'testcase.xsd';
  3    :schemaPath := '/public/testcase.xsd';
  4  end;
  5  /
PL/SQL procedure successfully completed.
SQL> call dbms_xmlSchema.deleteSchema(:schemaURL,4)
  2  /
Call completed.
SQL> declare
  2    res boolean;
  3    xmlSchema xmlType := xmlType(
  4  '<?xml version="1.0" encoding="UTF-8"?>
  5  <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xdb="http://xmlns.oracle.com/xdb" elementFormDefault="qualified" attribute
FormDefault="unqualified" xdb:storeVarrayAsTable="true">
  6     <xs:element name="root" type="rootType" xdb:defaultTable="ROOT_TABLE"/>
  7     <xs:complexType name="rootType" xdb:SQLType="ROOT_T">
  8             <xs:choice>
  9                     <xs:element ref="member1" xdb:SQLInline="false" xdb:defaultTable="MEMBER1_TABLE"/>
10                     <xs:element ref="member2" xdb:SQLInline="false" xdb:defaultTable="MEMBER2_TABLE"/>
11             </xs:choice>
12     </xs:complexType>
13     <xs:complexType name="member1Type" xdb:SQLType="MEMBER1_T">
14                             <xs:sequence>
15                                     <xs:element name="Member1.Child1" type="xs:string"/>
16                                     <xs:element name="Member1.Child2" type="xs:string"/>
17                             </xs:sequence>
18     </xs:complexType>
19     <xs:complexType name="member2Type" xdb:SQLType="MEMBER2_T">
20                             <xs:sequence>
21                                     <xs:element name="Member2.Child1" type="xs:string"/>
22                                     <xs:element name="Member2.Child2" type="xs:string"/>
23                             </xs:sequence>
24     </xs:complexType>
25     <xs:element name="member1" type="member1Type"  xdb:defaultTable="GLOBAL_MEMBER1_TABLE"/>
26     <xs:element name="member2" type="member2Type" xdb:defaultTable="GLOBAL_MEMBER2_TABLE"/>
27  </xs:schema>');
28  begin
29    if (dbms_xdb.existsResource(:schemaPath)) then
30      dbms_xdb.deleteResource(:schemaPath);
31    end if;
32    res := dbms_xdb.createResource(:schemaPath,xmlSchema);
33  end;
34  /
PL/SQL procedure successfully completed.
SQL> begin
  2    dbms_xmlschema.registerSchema
  3    (
  4      :schemaURL,
  5      xdbURIType(:schemaPath).getClob(),
  6      TRUE,TRUE,FALSE,TRUE
  7    );
  8  end;
  9  /
PL/SQL procedure successfully completed.
SQL> --
SQL> desc ROOT_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "root") STORAGE Object-relational TYPE "ROOT_T"
SQL> --
SQL> desc ROOT_T
ROOT_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
member1                                                                                      REF OF XMLTYPE
member2                                                                                      REF OF XMLTYPE
SQL> --
SQL> desc GLOBAL_MEMBER1_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "member1") STORAGE Object-relational TYPE "MEMBER1_T"
SQL> --
SQL> desc MEMBER1_T
MEMBER1_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
Member1.Child1                                                                               VARCHAR2(4000 CHAR)
Member1.Child2                                                                               VARCHAR2(4000 CHAR)
SQL> --
SQL> desc GLOBAL_MEMBER2_TABLE
Name                                                                                Null?    Type
TABLE of SYS.XMLTYPE(XMLSchema "testcase.xsd" Element "member2") STORAGE Object-relational TYPE "MEMBER2_T"
SQL> --
SQL> desc MEMBER2_T
MEMBER2_T is NOT FINAL
Name                                                                                Null?    Type
SYS_XDBPD$                                                                                   XDB.XDB$RAW_LIST_T
Member2.Child1                                                                               VARCHAR2(4000 CHAR)
Member2.Child2                                                                               VARCHAR2(4000 CHAR)
SQL> --
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'ROOT_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          ROOT_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."member1"                                              XMLTYPE
"XMLDATA"."member2"                                              XMLTYPE
ACLOID                                                           RAW
OWNERID                                                          RAW
12 rows selected.
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'GLOBAL_MEMBER1_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          MEMBER1_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."Member1.Child1"                                       VARCHAR2
"XMLDATA"."Member1.Child2"                                       VARCHAR2
ACLOID                                                           RAW
OWNERID                                                          RAW
12 rows selected.
SQL> select qualified_col_name, data_type from user_tab_cols where table_name = 'GLOBAL_MEMBER2_TABLE'
  2  /
QUALIFIED_COL_NAME                                               DATA_TYPE
SYS_NC_OID$                                                      RAW
SYS_NC_ROWINFO$                                                  XMLTYPE
XMLEXTRA                                                         XMLTYPEEXTRA
"XMLEXTRA"."NAMESPACES"                                          XMLTYPEPI
"XMLEXTRA"."EXTRADATA"                                           XMLTYPEPI
XMLDATA                                                          MEMBER2_T
SYS_TYPEID("XMLDATA")                                            RAW
"XMLDATA"."SYS_XDBPD$"                                           XDB$RAW_LIST_T
"XMLDATA"."Member2.Child1"                                       VARCHAR2
"XMLDATA"."Member2.Child2"                                       VARCHAR2
ACLOID                                                           RAW
OWNERID                                                          RAW
12 rows selected.
SQL> insert into ROOT_TABLE values( XMLType (
  2  '<root>
  3    <member1>
  4      <Member1.Child1>AAA</Member1.Child1>
  5      <Member1.Child2>BBB</Member1.Child2>
  6    </member1>
  7  </root>'))
  8  /
1 row created.
SQL> insert into ROOT_TABLE values( XMLType (
  2  '<root>
  3    <member2>
  4      <Member2.Child1>CCC</Member2.Child1>
  5      <Member2.Child2>DDD</Member2.Child2>
  6    </member2>
  7  </root>'))
  8  /
1 row created.
SQL> set long 1000 pages 20
SQL> --
SQL> select * from ROOT_TABLE
  2  /
SYS_NC_ROWINFO$
<root>
  <member1>
    <Member1.Child1>AAA</Member1.Child1>
    <Member1.Child2>BBB</Member1.Child2>
  </member1>
</root>
<root>
  <member2>
    <Member2.Child1>CCC</Member2.Child1>
    <Member2.Child2>DDD</Member2.Child2>
  </member2>
</root>
SQL>
SQL>
SQL>