16.3. Conceptual Query Languages
An information system may be modeled at any of four levels: conceptual, logical, physical, and external. In principle, it may also be queried at any of these levels. In practice however, although conceptual modeling is widely used, it is comparatively rare for systems to be queried at the conceptual level. Instead, queries are typically formulated either at the external level using forms, at the logical level using a language such as SQL, or at the physical level using a programming language. This section briefly indicates some problems with these lower level approaches and explains how these problems are avoided by conceptual query languages, especially those based on ORM.
At the external level, Query-By-Form ...
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