1. A computer-implemented method of abstract query composition based on user roles defined in a database abstraction model, the computer-implemented method comprising: providing the database abstraction model, which contains a plurality of logical field definitions defining a plurality of logical fields that map to a plurality of physical fields of one or more underlying physical databases, each of the plurality of logical field definitions specifying: (i) a logical field name and (ii) an access method comprising a function of one or more of the plurality of physical fields; wherein the database abstraction model further defines a set of user roles; the plurality of logical field definitions specifying at least two types of access methods selected from: (i) a simple access method mapping to a specified physical field; (ii) a filtered access method applying a specified filter to a physical field; and (iii) a composed access method mapping to a set of values generated from one or more physical fields based on a specified formula; prior to selecting any logical field to include in an abstract query desired to be composed, selecting, from the set of user roles, a plurality of user roles desired to have permission to execute the abstract query once composed, wherein the plurality of user roles is selected based on input from an administrative user of the database abstraction model; subsequent to selecting the plurality of user roles, determining, by operation of one or more computer processors, a group of permitted logical fields to which access is permitted for at least one of the selected plurality of user roles; generating output conveying: (i) the group of permitted logical fields as being permitted based on the selected plurality of user roles and (ii) a group of non-permitted logical fields as being non-permitted based on the selected plurality of user roles; subsequent to generating the output, selecting, from the group of permitted logical fields and based on input from the administrative user responsive to the generated output, one or more logical fields to include in the abstract query desired to be composed; composing the abstract query based on the selected one or more logical fields; and responsive to receiving, from a non-administrative user, a request to execute the composed abstract query, and upon determining that the non-administrative user has a role that matches at least one of the selected plurality of user roles defined in the database abstraction model, executing the composed abstract query in order to generate a set of query results, whereafter the set of query results is output for the non-administrative user.