Hierarchical data
- Hierarchical data is a common relational data pattern for representing tree-like data structures, such as an organizational structure, a project breakdown list, or even a family tree.
- In relational database model, One thing to remember is that flexibility in keys.
- We have the flexibility to design the database, it might be worth having multiple geometry types for certain data types.
- For example, having a city represented as a polygon would be useful to perform spatial queries to determine all points of interest within that city.
- At the same time, it is oftentimes more desirable to represent a city as a point on a map. The database allows you to do this by separating the attribute data from the features into their own table, and linking them together with a Primary Key/Foreign Key structure.
Primary Key:
- A Primary Key is an identifier for a record in a table.
Foreign Key:
- A Foreign Key is a reference to that same identifier in a different table, thus linking them together.
CREATE DATABASE testDB:
- We want to includes this tables to the database:
- Continent – Fields – Geom (Polygon), ID(Primary Key), Name, Etc
CREATE TABLE Continent (
ID int NOT NULL PRIMARY KEY,
Name varchar(255) NOT NULL,
Geom_Polygon varchar(255),
Age int
);
Country – Fields – Geom (Polygon), ID, Name, Continent ID(Foreign Key)
CREATE TABLE Country (
ID int NOT NULL PRIMARY KEY,
Name varchar(255) NOT NULL,
Geom_Polygon varchar(255),
Continent_id int FOREIGN KEY REFERENCES Continent (ID)
);Region:
- If there are different levels of regions within a country, then we would have them as different layers.
- So, if a country has regions called districts, and a number of districts combine to form a state, which then combine to form the country, you would have a layer for each type.
- Reg_State – Fields – Geom (Polygon), ID (Primary Key), Name, Country ID, Etc
CREATE TABLE Reg_State (
ID int NOT NULL PRIMARY KEY,
Name varchar(255) NOT NULL,
Geom_Polygon varchar(255),
Country_id int FOREIGN KEY REFERENCES Country(ID)
);Cities:
- Have a table that contains attributes for each city, but no geometry.
- Have geometry tables with different geometries, like point or polygon, that link to the main city table.
- City_Info – Fields – CityID (Primary key), Name,Reg_District ID (Foreign Key), Etc,
CREATE TABLE City_Info (
CityID int NOT NULL PRIMARY KEY,
Name varchar(255) NOT NULL,
Reg_District_id int FOREIGN KEY REFERENCES District(ID)
);City_Pt – Fields – Geom (Point), ID, Name, CityID (Foreign Key)
CREATE TABLE City_Pt (
ID int NOT NULL,
Name varchar(255) NOT NULL,
Geom_Point varchar(255),
CityID int FOREIGN KEY REFERENCES City_Info(CityID )
);City_Poly – Fields – Geom (Polygon), ID, Name, CityID (Foreign Key)
CREATE TABLE City_Poly (
ID int NOT NULL,
Name varchar(255) NOT NULL,
Geom_Polygon varchar(255),
CityID int FOREIGN KEY REFERENCES City_Info(CityID )
);This is the one of the ways of setting up the database, again it depends on your specific needs for being able to link different pieces of data together.
- Once the table structure is determined, the next part will be to set up queries to retrieve the information you want, for inclusion in a report or some sort of viewing application.
