Abstract: A system, method and user interface facilitating hierarchical (e.g., tree-based) rule composition with natural language inline editing. For example, the system can combine a familiar hierarchical structure, such as a computer tree, and inline editing of natural language based logical expression(s) to provide a general purpose logical expression builder. In one example, the system facilitates construction and/or editing of business rule(s) based, at least in part, upon parameterized format string definition(s) and composable vocabulary definition(s). The system includes a rule composer and a display component. The rule composer facilitates creation, modification and/or viewing of a rule, for example, based upon a user input. The display component displays hierarchical information associated with the rule.