复杂对象嵌套结构的规范化

Normalization of Nested Structure for Complex Objects

本文将关系模型中的函数依赖、多值依赖、规范化等概念扩展到具有嵌套结构的复杂对象模型，并在函数依赖和多值依赖中融进了实体联系的语义，给出了规范化的方法和步骤．在最后的范式中，不存在不完全嵌套，在嵌套结构的每一层上，仅存在单属性的关键字，相当于关系模型中的ＢＣＮＦ范式．这样的范式可消除冗余，避免更新异常，提高查询效率，保证嵌套结构可简洁而正确地表达实体联系，且不存在平面式的联系类．

In this paper, the author extends the concepts of functional dependency, multiple valued dependency, normal form and normalization in relational model to complex object model with nested structure. The semantics of entity relationship are captured in functional dependency and multiple valued dependency. The approaches and steps of normalization are proposed. In final normal form, there exists no any incomplete nesting, and on every level of nested structure there exists only the key with single attribute, which corresponds to the BCNF normal form in relational model. It could not only make redundancy minimum, avoid anomalies of update, but also improve query performance, guarantee to correctly and simply express entity relationship with nested structure and without flat entity relationship classes.