Transcript Object-Oriented Data Model

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
Humanoriented
Reality
Conceptual Model
Logical Model
Computeroriented
Physical Model
Increasing
Abstraction
Levels of Data
Abstraction
Conceptual Model
Real World
Objects and
relationships
Logical Model
Physical
Model
Database
Schema
Diagrams
And lists
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 can
(3)beCharacteristics
Every field
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

Advantages
- Flexible, no structure restrictions for search
- Easy to understand
- Less data redundancy

Disadvantages
- It can be time consuming to search matching values



Objects
4 (4) Object-Oriented Data Model
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
Fish
A head and a body, feed
A head and a body, feed
Four legs, sit
Fins, swim

4 (4) Object-Oriented Data Model
Encapsulation
- Data and functions are combined in one object

4 and
(4) aggregation
Object-Oriented
Association
Inhabitation
Habitat
Fish
inhabitant
location:
time:
weight:
habitat
location:
time:
prey biomass:
temperature:
Aquatic System
location:
time:
predator weight:
prey biomass:
temperature:
Data Model
4 (4) Advantages and Disadv

Advantages
- 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
features geometry
components
Spatial Types – OGC Simple
Features
Geometry
SpatialReferenceSystem
Composed
Type
Relationship
Point
Curve
Surface
LineString
Polygon
Line
LinearRing
GeometryCollection
MultiSurface
MultiCurve
MultiPolygon
MultiLineString
MultiPoint
Object-Relational Databases
Readings

Chapter 3
Object-Oriented and ObjectRelational GIS DBMS


Object-oriented (OODBMS)
- Based on OO concept to store state and
of GIS objects in databases
- Provide OO query tools
- Commercially not successful
behavior
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 twodimensional row, column structure. Each single
table stores an object class.



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 implementationindependent 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

Feature has state, behavior, and relationships with other
objects and features





Stored in feature datasets and feature classes.
Object class


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
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.