Research on accessing databases in natural language usually employs an intermediate form for the mapping process from natural language to database languages. However, much effort is needed to bridge the gap between the existing intermediate forms and the database languages. In this paper, we present a methodology to map natural language constructs into relational algebra through E-R representation. This methodology employs a logical form to represent the natural language queries. The logical form has the merits that it can be mapped from natural language constructs by referring to the Entity-Relationship conceptual schema and can be efficiently transformed into relational algebra for query execution. The whole process provides a clear and natural framework for processing natural language queries to retrieve data from database systems.