You might also want to check out [SOA Made Simple|http://www.packtpub.com/service-oriented-architecture-made-simple/book] , co-authored by Oracle ACE Directors Lonneke Dikmans and Ronald van Luttikhuizen.
SOA is not a technology stack it is an architectural approach to service enabling capabilities within a business. Oracle Funsion Middleware is Oracles implementation of a tool set that is designed to help implement SOA.
There are plenty of guides to Oracle SOA Suite and OSB, but I would read more around what SOA actually is, what it aims to do etc. There are many books that cover this.
You can then decide on which implementation best suits your requirements (Oracle IMO is the best currently available). Imagine you learnt Java without learning the principals of OO programming, you could end up with one class doing everything. The same applies to SOA, understand the principals first.
I can recommend this books:
- [SOA Made Simple|http://www.packtpub.com/service-oriented-architecture-made-simple/book] by Lonneke Dikmans and Ronald van Luttikhuizen
- [Do More with SOA Integration: Best of Packt|http://www.packtpub.com/soa-integration-automation-business-processes-books-best-of-packt/book] , edited by Carl Jones (but some chapters become out of date)
- [SOA-Based Enterprise Integration|http://www.amazon.com/SOA-Based-Enterprise-Integration-Step-Step/dp/0071605525] by Waseem Roshen.