Access XML Data as a Remote Oracle Database

The Oracle Database Gateway for ODBC and Heterogeneous Services technology enable you to connect to ODBC data sources as remote Oracle databases. This article shows how to use the CData ODBC Driver for XML to create a database link from XML to Oracle and to query XML data through the SQL*Plus tool. You can also create the database link and execute queries from SQL Developer.

Connect to XML as an ODBC Data Source

Information for connecting to XML follows, along with different instructions for configuring a DSN in Windows and Linux environments.

See the Getting Started chapter in the data provider documentation to authenticate to your data source: The data provider models XML APIs as bidirectional database tables and XML files as read-only views (local files, files stored on popular cloud services, and FTP servers). The major authentication schemes are supported, including HTTP Basic, Digest, NTLM, OAuth, and FTP. See the Getting Started chapter in the data provider documentation for authentication guides.

After setting the URI and providing any authentication values, set DataModel to more closely match the data representation to the structure of your data.

The DataModel property is the controlling property over how your data is represented into tables and toggles the following basic configurations.

• Document (default): Model a top-level, document view of your XML data. The data provider returns nested elements as aggregates of data.
• FlattenedDocuments: Implicitly join nested documents and their parents into a single table.
• Relational: Return individual, related tables from hierarchical data. The tables contain a primary key and a foreign key that links to the parent document.

See the Modeling XML Data chapter for more information on configuring the relational representation. You will also find the sample data used in the following examples. The data includes entries for people, the cars they own, and various maintenance services performed on those cars.

Windows

If you have not already, first specify connection properties in an ODBC DSN (data source name). This is the last step of the driver installation. You can use the Microsoft ODBC Data Source Administrator to create and configure ODBC DSNs.

Note: If you need to modify the DSN or create other XML DSNs, you must use a system DSN and the bitness of the DSN must match your Oracle system. You can access and create 32-bit DSNs on a 64-bit system by opening the 32-bit ODBC Data Source Administrator from C:\Windows\SysWOW64\odbcad32.exe.

Linux

If you are installing the CData ODBC Driver for XML in a Linux environment, the driver installation predefines a system DSN. You can modify the DSN by editing the system data sources file (/etc/odbc.ini) and defining the required connection properties.

/etc/odbc.ini

For specific information on using these configuration files, please refer to the help documentation (installed and found online).

Set Connection Properties for Compatibility with Oracle

The driver provides several connection properties that streamline accessing XML data just as you would an Oracle database. Set the following properties when working with XML data in SQL*Plus and SQL Developer. For compatibility with Oracle, you will need to set the following connection properties, in addition to authentication and other required connection properties.

• MapToWVarchar=False

  Set this property to map string data types to SQL_VARCHAR instead of SQL_WVARCHAR. By default, the driver uses SQL_WVARCHAR to accommodate various international character sets. You can use this property to avoid the ORA-28528 Heterogeneous Services data type conversion error when the Unicode type is returned.

• MaximumColumnSize=4000

  Set this property to restrict the maximum column size to 4000 characters.

• IncludeDualTable=True

  Set this property to mock the Oracle DUAL table. SQL Developer uses this table to test the connection.

Linux Configuration

In Linux environments, Oracle uses UTF-8 to communicate with the unixODBC Driver manager, whereas the default driver encoding is UTF-16. To resolve this, open the file /opt/cdata/cdata-driver-for-xml/lib/cdata.odbc.xml.ini in a text editor and set the encoding.

cdata.odbc.xml.ini

Configure the ODBC Gateway, Oracle Net, and Oracle Database

Follow the procedure below to set up an ODBC gateway to XML data that enables you to query live XML data as an Oracle database.

1. Create the file initmyxmldb.ora in the folder oracle-home-directory/hs/admin and add the following setting:

   initmyxmldb.ora

   HS_FDS_CONNECT_INFO = "CData XML Sys"
2. Add an entry to the listener.ora file. This file is located in oracle-home-directory/NETWORK/admin.

   If you are using the Database Gateway for ODBC, your listener.ora needs to have a SID_LIST_LISTENER entry that resembles the following:

   listener.ora

   SID_LIST_LISTENER = (SID_LIST = (SID_DESC = (SID_NAME = myxmldb) (ORACLE_HOME = your-oracle-home) (PROGRAM = dg4odbc) ) )

   If you are using Heterogeneous Services, your listener.ora needs to have a SID_LIST_LISTENER entry that resembles the following:

   listener.ora

   SID_LIST_LISTENER = (SID_LIST = (SID_DESC = (SID_NAME = myxmldb) (ORACLE_HOME = your-oracle-home) (PROGRAM = hsodbc) ) )

3. Add the connect descriptor below in tnsnames.ora, located in oracle-home-directory/NETWORK/admin:

   tnsnames.ora

   myxmldb = (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=localhost)(PORT=1521)) (CONNECT_DATA=(SID=myxmldb)) (HS=OK) )
4. Restart the listener.

5. Test the configuration with the following command:

   tnsping myxmldb

6. Open SQL*Plus and create the database link with the command below:

   CREATE DATABASE LINK myxmldb CONNECT TO "user" IDENTIFIED BY "password" USING 'myxmldb';

You can now execute queries in SQL*Plus like the one below (note the double quotation marks around the table name):