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.
Hierarchical data

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.

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