Former Oracle collegueus and business parnerts wrote a nice cok book on the usages of Oracle Service Bus. The book is full of examples and guide you through the working and usage of the Oracle Service Bus. The is very technical of useful for developers who just ant to start the OSB. Experienced developers will use this book for the complete examples on the different technologies using OSB, such as JMS, EJB.
When you use this book, it is expected that you understand the concepts of XML, XLST, WSDL, WebServices, JMS and SOAP and basic knowledge of SQL. This is not explained in the book. Which is a advantage! Refer to the w3schools for such things.