Geographic Information Systems GIS Data 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 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)

Levels of Data Abstraction Human-oriented Reality Conceptual Model Increasing Abstraction Logical Model Computer-oriented Physical Model

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

Data Models Vector data model Raster data model courtesy: Mary Ruvane, http://ils.unc.edu/

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

3 Database Functions Map librarian and tiles

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 two dimensional 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 filed is common to both files A link table can be created with needed attributes, without actually taking storage space

4 (3) Advantages and Disadv - Flexible, no structure restrictions for search - Easy to understand - Less data redundancy Disadvantages - It can be time consuming to search matching values

4 (4) Object-Oriented Data Model Objects  Attributes  Operations

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 A head and a body, feed Four legs, sit Fish A head and a body, feed Fins, swim

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

4 (4) Object-Oriented Data Model Association and aggregation Inhabitation Habitat Fish location: time: prey biomass: temperature: inhabitant habitat location: time: weight: Aquatic System location: time: predator weight: prey biomass: temperature:

4 (4) Advantages and Disadv - Easy for modeling and the representation is close to human perception - Reduce the complexity of software development Disadvantages

4 (4) Object-Relational Databases Uses 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 Object-Relational Databases features geometry components

Spatial Types – OGC Simple Features Geometry SpatialReferenceSystem Composed Type Relationship Point Curve Surface GeometryCollection LineString Polygon MultiSurface MultiCurve MultiPoint Line LinearRing MultiPolygon MultiLineString

Object-Relational Databases

Readings Chapter 3

Object-Oriented and Object-Relational GIS DBMS Object-oriented (OODBMS) - Based on OO concept to store state and behavior of GIS objects in databases - Provide OO query tools - Commercially not successful Object-Relational (ORDBMS) - Extend RDMS to handle GIS objects - Current Geographic Databases are ORDBMS

Main Types of DBMS in GIS Relational (RDBMS) RDMS is the most popular type of DBMS Over 95% of data in DBMS is in RDBMS DB2; SQL Server, Access; Oracle; Informix A relational database comprises tables, a two-dimensional row, column structure. Each single table stores an object class. Main Types of DBMS in GIS Rows contain objects Columns contain object properties or attributes Data stored in intersection of row and column is value

1. Components of Geographic Data

Conceptual model Human-oriented, conceptual description of the main types of objects and processes relevant to a problem domain e.g. objects/fields Logical model Implementation oriented, but implementation-independent representation of reality; Often in the form of diagrams and lists e.g. Raster/vector Physical model The actual application in a GIS; describe the exact files or database tables E.g. A shapefile is composed of a .shp file for geometry, .dbf for attributes

Feature Object class Feature class Feature dataset Feature has state, behavior, and relationships with other objects and features State: geometry and other attributes Behavior: default values, attribute domains, subtypes, split/merge policy, relationship rules, topology rules, connectivity rules Relationships: thematic relationships and topology Stored in feature datasets and feature classes. Object class An object class is a regular database table in a geodatabase. Feature class A collection of features with the same type of geometry An object class with a geometry, each row is a feature. Feature dataset Contains feature classes sharing the same spatial reference Required for geometric network and topologies