A natural language tool is provided for specifying a subset of data. The data may be dynamic and have elements which are inter-related. The inter-related data is specified using a natural language expression. The natural language tool enables a user to construct a natural language expression using embedded fields. A user may configure, add and remove fields within the expression. A natural language expression contains at least two configurable fields. The fields of an expression have a tiered relationship. When a higher tiered field is changed, one or more lower tiered fields may be changed in response to the higher field change.