An Overview of the Entities in the Database
The DGSD divides data into four categories. These are Entities, Historical Instances, Point Locations, and Attributes. In addition, five Data Definition tables record the categories of information modeled in the main tables.
The data model for the DGSD database.
1. Entities
The DGSD table that lists named places is called the Entity table. The DGSD tracks political entities that changed, sometimes dramatically, over time. Therefore, it utilizes a numeric key value as a stable identifier for each unique place. Numerous items of data, representing multiple names, ranks, and parent-child relationships, can be linked to the same numeric key value so long as they are all associated with an entity that can be considered to be a single place. All of the tables in the database are linked to the Entity table.
The Historical Instance table records the events that resulted in changes to named entities and the relationships between them.
The locations of entities are recorded using decimal longitude and latitude, referred to within the tables as x/y coordinates. Following the practice of the China Historical GIS and the conventions of Song sources, the DGSD records point locations for prefectures rather than polygonal boundaries. Circuits have fully polygonal boundaries based on the CHGIS.
4. Attributes
All of the other information that Hope Wright recorded about entities is held in the Attribute table. The Attribute table includes information about an entity’s military ranks, demographic profile, and non-georeferenced constituent places such as cantons, mines, and markets. The DGSD records all of the attributes that appear in the Alphabetical List.
In addition to the four tables of the main database, five additional tables record detailed information about the data types tracked in the main database. These tables record 11 feature types, 45 attribute types, 12 change types, 33 military and civil rank types, and 8 sources from which the information in the DGSD was derived.