1. A method of mapping objects of an application to a data source, comprising: defining using a computer processor a model that transparently maps an existing object class to an existing data source schema of said data source including defining a relationship between columns of tables of the data source schema with properties of the object class at least in part by: interactively associating, using a computer processor and using a series of displays, said object class with a corresponding data structure of said data source schema, where interactively associating includes automatically generating a model and displaying the model, and allowing an user to interactively customize the displayed model; and configuring using a computer processor said model to use said association at runtime of the application to synchronize a data value of a persistent property in an instance of said object class with a corresponding stored value stored in said data structure, including by receiving from the application at application run time a request to fetch said instance of said object class and using the model at application run time to generate in response to the request, at the run time of the application, one or more statements to retrieve said stored value stored in said data structure; wherein using said association to synchronize a data value of said persistent property in an instance of said object class with a corresponding stored value stored in said data structure comprises propagating to said instance a modification to said stored value as stored in said data structure.