The link to download the file (called Oracle SOA Composite Editor):
http://www.oracle.com/technology/products/jdev/101/update/fmw_products.xml

To download the file directly:
http://download.oracle.com/otn/java/jdeveloper/111/extensions/soa-jdev-extension.zip

After download the file, you can install it using the Check for update option in Jdeveloper.

As you can see in the following screenshot, the option is available under the Help menu.

Then select the option "Install From Local File", and select the location where you put the zip file.

After that you will see that the Oracle SOA Composite Editor will be installed and Jdeveloper will restart.

To verify the installed extension, You can go to File -> New section and you will see the new option "SOA Tier".

If you chose that you will have the following templates as an option:

Then, you are ready to work in your SOA project!.

First of all, we must download the Jdeveloper's installer from http://www.oracle.com/technology/software/products/jdev/index.html
As you can read there, it's certified on Windows NT/2000/XP/Vista, Linux, Macintosh and Supported on any platform that runs JDK 6.

In this case, the installation process will run under Windows XP operating system.

The file downloaded is called 111110_jdev_studio_5407.exe , after clicking on it the Oracle Installer is launched and the following window is presented.

Will continue...