HowTo Use Oracle Database System with Jena2

Windows Platforms

Oracle is certified for RedHat Linux versions AS and ES. No other RedHat versions are supported by Oracle (for details, see http://otn.oracle.com/tech/linux/index.html). Unfortunately, AS and ES are not free. However, we were able to run the Jena2 test suite with Oracle using two free RedHat distributions, 7.2 and 9.0. All tests passed however there is a minor warning that we do not think will affect Jena2 users (see Known Bugs). Consequently, we can recommend the following Oracle version with Jena2. Note that installing Oracle under Linux can be tricky. For tips on installing and running Oracle under RedHat Linux, see http://www.puschitz.com/InstallingOracle9i.html and http://linux.oreillynet.com/lpt/a/4141.

A user account and password are required to access the Oracle server. Typically, Oracle is installed with a demo database and user account that may be used for testing and experimentation. In the examples below, we assume the use of this default account (user name is scott and password is tiger). If you have your own Oracle user name and password, please use those values for DB_USER, DB_PASSWD. The DB_URL value should be set as indicated below.

In order to run Jena2 programs with Oracle, make sure that your CLASSPATH includes the jar files for classes12.jar and nls_charset12.jar.

Connecting Your Jena Program to Oracle

Jena supports both memory models and database models. In general, a Jena program may use both types of models identically. However, there are some differences in how the models are created. Creating a memory model can be done with a single Jena call. Creating a database model, or opening a previously created one, requires several steps as as follows.

1. Important:
   Edit the source file com.hp.hpl.jena.db.impl.Driver_Oracle.java.
   Uncomment the Oracle import commands at the top of the file:
    import oracle.jdbc.OracleResultSet;
    import oracle.sql.BLOB;
   Comment-out the stubbed-out interfaces named BLOB and OracleResultSet.
2. Load the JDBC driver. This enables the Jena program to communicate with the database instance.
3. Create a database connection. This creates a Java object for a database connection.
4. Create or open a model on the connection. This connects to the database and creates an empty model or opens a previously created model.

Steps 2-4 are illustrated in the following Java code.

// Load the Driver

String className = "oracle.jdbc.driver.DriverOracle" // path of driver class

Class.forName (className); // load driver

String DB_URL = "jdbc:oracle:oci:@"; // URL of database server

String DB_USER = "scott"; // database user id

String DB_PASSWD = "tiger"; // database password

String DB = "Oracle"; // database type

// Create database connection

IDBConnection conn = new DBConnection ( URL, DB_USER, DB_PASSWD, DB );

// Create a model in the database

ModelMaker maker = ModelFactory.createModelRDBMaker(conn);

ModelRDB m = (ModelRDB) maker.createModel ();

< your Jena code to work with the model goes here >

// Remove the model. NOTE: this deletes the model from the database.

// Subsequent attempts to open this model will fail.

m.remove();// NOTE: remove deletes the model from the database

// Close the database connection

conn.close();

// Alternative to creating an unnamed model ...

// Create a named model

ModelRDB m = maker.createModel("myName");

... later, or in another Jena application ...

// Open a named model.

ModelRDB m = maker.openModel("myName");

Usage Notes

Jena stores all models in a single database using whatever database (name) specified on the database connection. See the Jena Database Release Notes for details on the physical layout.

Known Bugs

1. We encountered problems with BLOBs when using the Oracle thin driver to access an Oracle database running on the Linux operating system, so we recommend use of the oci driver when using Linux.
2. Under Linux, in running the database TestPackage, we get a Java warning that an SQLException was thrown when a thread attempts a next operation on a database iterator over a closed database connection. This appears to be a timing problem involving interaction with a finalize routine. The test returns the correct result. The warning does not occur under WinXP.

Oracle Utility Commands

Some Jena users may wish to occasionally access the Oracle database directly to determine if changes have taken effect. Some useful Oracle commands are listed here (replace the names in italics by names for your database instance). To use them, start the Oracle command line interface: SQLPlus username/password

List Tables: select * from TAB;

List Sequences: select * from SEQ;

Count All Rows in a Table: select count(*) from tableName;

List All Rows in a Table: select * from tableName;

Execute a SQLPlus command file: @<filename> where <filename> is the path of a file containing SQLPlus commands

Exit SQLPlus: quit;