Geographic Information Systems GIS Databases 1 GIS Databases

Geographic Information Systems GIS Databases

1 GIS Databases A database is a shared collection of data with secure controlled access ► Data are stored independently of their applications ► A GIS database contains geographic data ► ►A database management system (DBMS) is a collection of software programs that facilitates the efficient and effective storage and access of data ► A GIS DBMS

2 Levels of Data Abstraction ► Conceptual data model - user's perception of the real world ► Logical data model - a formal description of the data model ► Physical data model - physical storage of the data (e. g. , format, order, path)

2 Levels of Data Abstraction … Humanoriented Reality Conceptual Model Logical Model Computeroriented Physical Model Increasing abstraction

3 Database Functions ► Records, fields, and keys - a row is a record - a column is a field

3 Database Functions … ► Map librarian and tiles

3 Database Functions … ► Adding, updating and deleting records ► Extracting information from data ► Maintaining data security and integrity ► Supporting applications

4 Database Data Models (Logical Models) Hierarchical data model ► Network data model ► Relational data model ► Object-oriented data model ►

4 (3) Relational Data Model The database consists of several tables ► A row is a record and a column is a field ►

4 (3) Characteristics ► Every field can be used as a key in a search ► A cross file search can be done by join, as long as at least one field is common to both files ► A link table can be created with needed attributes, without taking actual storage space

4 (3) Advantages and Disadv ► Advantages - Flexible, no structure restrictions for search - Easy to understand - Less data redundancy ► Disadvantages - There ay be 1: M or N: M relationships between tables

4 (4) Object-Oriented Data Model ► Encapsulation ► Objects, attributes, processes Inheritance ► Association and aggregation ►

4 (4) Object-Oriented Data Model. . ► Encapsulation - Data (attributes) and functions (processes) are combined in one object

4 (4) Object-Oriented Data Model. . ► Inheritance - Data and functions are organized in a hierarchy - Objects inherit characteristics and functions of their ancestor objects Animals A head and a body, feed Mammals Fish A head and a body, feed Four legs, sit Fins, swim

4 (4) Object-Oriented Data Model. . ► Association and aggregation a member of vs. a part of Inhabitation Habitat Fish inhabitant location: time: weight: habitat location: time: prey biomass: temperature: Aquatic System location: time: predator weight: prey biomass: temperature:

4 (4) Advantages and Disadv ► Advantages - Easy for modeling and the representation is close to human perception - Reduce the complexity of software development ► Disadvantages - Most existing object-based systems are a hybrid of relational and object-based databases

4 (4) Object-Relational Databases ► Use an enriched set of graphic element types on top of the three basic types of points, lines, and polygons

Object-Relational Databases. . ► two levels of geometries: features geometry, and components of features geometry components

Readings ► Chapter 3

Object-Relational Databases. .

Levels of Data Abstraction … Conceptual Model Real World Objects and relationships Logical Model Physical Model Database Schema Diagrams And lists

Spatial Types – DB 2 Spatial Extender Oracle Spatial Arc. SDE/Arc. GIS Server