Database Management
Reference Manual
Introduction to Database Concepts
: Primary Database Hierarchy
Primary Database Hierarchy
Hierarchical Data Model
Each database consists of a hierarchy of elements. The allowed hierarchy is defined in a Database Schema. The database schema is the 'meta data', i.e. it is data about data. Database Schemas cannot be modified by users. The Database Schema for each database type is listed in the data model reference manual. An example of part of the Database Schema for MODEL databases is shown below:
This schema shows which elements are allowed where. For example, a WORLD may own a SITE, or GROUPWORLD, whereas a SITE may own a ZONE, BOUNDARY, DRAWING or GROUND model.
The same element type may occur in more than one place in the schema. In the above example it can be seen that a BOUNDARY element may occur below a SITE or a ZONE.
All database schemas have a WORLD element at the root.
1974 to current year.
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