FileMaker and Access combine interface and front end with the back end. Neither are enterprise/corporate solutions. SQL databases just focus on the storage and access of data. ANSI SQL is supported by most of the big brands but each have their own features that are not standard. If you are used to File Maker, and Access this will be a big leap and you will likely spend some amount of time convinced that those products are superior. You will be wrong, I can assure you, but it's a normal part of the learning process.
RDMS stands for Relational Database Management System. There are other types, like Object Oriented Databases and the new and trendy Document Oriented ones. SQL really just refers to the language we use to access a Relational Database. Each of the products implement themselves a bit differently.
So in closing my main warning still applies. You can implement whatever relational database you'd like, just be sure you don't rely heavily on any of the proprietary features of a specific product. If you do, then migrating will be much more difficult. It's important to know what's standard and what's a feature of the specific product.
