So if I understand correctly, you want a sort of Data class that allows you to read and write to it without knowing the underlying details of how it works.
You can do this by using an AbstractFactory pattern which provides these Data classes for writing/reading. Each factory will have its own implementation with a method to initialize and a method to shutdown. While your file system factory won't likely need to do much, your database factory will need to establish a connection and then close it, for instance. You must be able to do all this without passing parameters to the factory. I'll be honest, I'm not too familiar with actionscript, but in Java you could say, load a configuration file and the configuration file provides connection info or whatever else required for the factory to initialize.
Each factory type would return a specific implementation of Data class that does the actual work of writing/reading from that source. My advice is that the location is provided upon calling the factory and that location remains immutable. In other words, to write to a different location, you'd need to call the factory again with a different address.
In this way you're hiding implementation details from its usage in your program, which is fine. However, this only works so long as the usage remains the same between all Data class implementations. For instance, if you're having to determine the type of a Data class implementation so you can cast it to a DatabaseData instance and then call "BulkInsert", you should not be using this pattern nor should you be hiding implementation details. The whole point is that you should only ever need an instance of Data class.
I hope that answers your question!