分层数据库模型 - 物理指针
hierarchical database model - physical pointers
我正在阅读一本关于数据库的书，我想知道是否有人可以解释一些我无法理解/想象的东西。我使用过关系数据库并了解外键等。我的问题是，分层数据模型中的 "physical pointer" 是什么？
The earlier hierarchical data model is suitable for data structures that are naturally hierarchical, with each data structure placed at a certain level in the hierarchy. However, in the business arena, many of the data structures and their relationships cannot be readily placed in a hierarchical arrangement. The network data model evolved to dispense with the arbitrary restriction of the hierarchical model. Nevertheless, in both of these models, you need physical pointers to connect related data occurrences. This is a serious drawback because you have rewrite the physical addresses in the data records every time you reorganize the data, move the data to a different storage area, or change over to another storage medium. The relational model establishes the connections between related data occurrences by means of logical links implemented through foreign keys.
Ponniah, P. (2003) Database Design and Development: An Essential Guide for IT Professionals [在线]，新泽西州霍博肯，John Wiley & Sons。可在 http://onlinelibrary.wiley.com/book/10.1002/0471728993
物理指针是指示某物所在位置的任何值，例如内存地址、数组或集合中的位置、文件系统路径、OID 等
相比之下，关系模型通过事物自身的属性——自然键或分配的代理键来识别事物。这为 DBMS 添加了一个抽象层和复杂性，但将用户与系统数据结构的组织隔离开来。
例如，在分层数据结构中，每个子记录可能包含其父记录的地址，而父记录可能包含其子地址的数组。
我正在阅读一本关于数据库的书，我想知道是否有人可以解释一些我无法理解/想象的东西。我使用过关系数据库并了解外键等。我的问题是，分层数据模型中的 "physical pointer" 是什么？
The earlier hierarchical data model is suitable for data structures that are naturally hierarchical, with each data structure placed at a certain level in the hierarchy. However, in the business arena, many of the data structures and their relationships cannot be readily placed in a hierarchical arrangement. The network data model evolved to dispense with the arbitrary restriction of the hierarchical model. Nevertheless, in both of these models, you need physical pointers to connect related data occurrences. This is a serious drawback because you have rewrite the physical addresses in the data records every time you reorganize the data, move the data to a different storage area, or change over to another storage medium. The relational model establishes the connections between related data occurrences by means of logical links implemented through foreign keys.
Ponniah, P. (2003) Database Design and Development: An Essential Guide for IT Professionals [在线]，新泽西州霍博肯，John Wiley & Sons。可在 http://onlinelibrary.wiley.com/book/10.1002/0471728993
物理指针是指示某物所在位置的任何值，例如内存地址、数组或集合中的位置、文件系统路径、OID 等
相比之下，关系模型通过事物自身的属性——自然键或分配的代理键来识别事物。这为 DBMS 添加了一个抽象层和复杂性，但将用户与系统数据结构的组织隔离开来。
例如，在分层数据结构中，每个子记录可能包含其父记录的地址，而父记录可能包含其子地址的数组。