1. Object-Based Vector Data Model
Chapter 4
Object-Based Vector Data Model

2. CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL
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CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL
4.1 Object-based Data Model
4.2 The Geodatabase Data Model
4.3 Interface
4.4 Topology Rules
4.5 Advantages of the Geodatabase Data Model

3. CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL
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CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL
Georelational data model is a split system
Object-based model stores spatial and attribute data together rather than in a split system
Geometry (spatial data) stored as an attribute along with other attributes
Eliminates use of split system and need for data synchronization

4. 4.1 Object-Based Data Model
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4.1 Object-Based Data Model
Windows environment
Menus, icons, etc. instead of command line
Model treats spatial data as objects
Object can represent a spatial feature (road or lake)
Object can also represent a layer or the coordinate system on which the layer is based

5. Two Differences between Georelational and Object-Based Models
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Two Differences between Georelational and Object-Based Models
1. Stored in single system rather than split

6. A Land Use Data Set Figure 4.1
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A Land Use Data Set
Figure 4.1
The object-based data model stores each land use polygon in a record. The Shape field stores the spatial data of land use polygons. Other fields store attribute data such as Landuse_ID and Category.

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A Major Breakthrough
Using a single system is a major breakthrough because software developers must regularly deal with issues of data storage and data file structure.

8. Second difference between georelational and object-based data models
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Second difference between georelational and object-based data models
2. Allows spatial feature (object) to be associated with properties and methods
Property - an attribute or characteristic of an object
Method - a specific action that can be performed on an object

9. 4.1.1 Classes Set of objects with similar characteristics
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4.1.1 Classes
Set of objects with similar characteristics
Hierarchical structure
Feature class - data set that stores features of the same geometry type in the data base.

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Figure 4.2
The Geometry property of the Feature class can differentiate the object types of point, line, and polygon.

11. 4.1.2 Relationships Between Classes
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4.1.2 Relationships Between Classes
Following grouping objects into classes, we must then sort out the relationships between classes
Association, aggregation, composition, type inheritance, and instantiation

12. Association How one class may be associated with another
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Association
How one class may be associated with another
Streets and signal lights
Street can be associated with one or more street lights but with only one coordinate system
Figure 4.3 Two examples of class associations

13. Aggregation Whole-part relationships between classes
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Aggregation
Whole-part relationships between classes
One class is a part of another class
State is an aggregate of counties

14. Composition Similar to aggregation The composite owns the parts
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Composition
Similar to aggregation
The composite owns the parts
Highway may have from zero to any number of rest areas, and the lifetime of the rest areas are controlled by the existence of the highway

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Type Inheritance
Defines relationship between a superclass and a subclass
Subclass is a member of the superclass and inherits the properties and methods of the superclass
Subclass can have additional properties not common to the rest of the superclass

16. Figure 4.4 An example of type inheritance
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Figure 4.4 An example of type inheritance

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Instantiation
Object of one class may be created from objects of another class
Figure 4.5 An example of instantiation

18. Summary 4.1.2 Relationships Between Classes
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Summary
4.1.2 Relationships Between Classes
Following grouping objects into classes, we must then sort out the relationships between classes
Association, aggregation, composition, type inheritance, and instantiation

19. 4.2 The Geodatabase Data Model
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4.2 The Geodatabase Data Model
Third major ESRI data model following coverage model of 1980s and shapefile model of 1990s
ArcObjects - collection of thousands of objects, properties, and methods

20. 4.2.1 Geometric Representation of Spatial Feature
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4.2.1 Geometric Representation of Spatial Feature
Uses geometries of point, polyline, and polygon to represent vector-based spatial features
Point - simple feature with a point or multipoint feature with a set of points
Polyline - set of line segments which may or may not be connected
Polygon - Made of one or many rings
Ring - set of connected, closed, nonintersecting line segments
See Box 4.1, page 65 of text

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Figure 4.6
The linear measures (M) of a route are stored with X- and Y-coordinates in a geodatabase. In this example, the M values are in miles, whereas the X- and Y-coordinates are in feet.

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Figure 4.7
A route, shown here as a thicker, gray line, is built on a polyline with linear measures in a geodatabase.

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4.2.2 Data Structure
Geodtabase data model distinguishes between feature classes and feature datasets
Feature class
Stores spatial data of the same geometry type
Feature dataset
Stores feature classes that share the same coordinate system and area extent

24. Feature Classes and Feature Datasets
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Feature Classes and Feature Datasets
Feature class is like a shapefile in having simple features
Feature dataset is similar to a coverage in having multiple datasets based on the same coordinate system and area extent

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Figure 4.8
In a geodatabase, feature classes can be standalone feature classes or members of a feature dataset.

26. 4.3 Interface Set of externally visible operations of an object
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4.3 Interface
Set of externally visible operations of an object
Objects have properties and methods, which are hidden
To use them we work with an interface
Software issue. Users do not deal directly with ArcObjects, which are accessed through menus, icons, and dialogs (GUI interface)

27. Interface Encapsulation Inheritance Polymorphism
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Interface
Encapsulation
Hide properties and methods of an object so that the object can only be accessed through the predefined interface
Inheritance
Stipulates that an object can inherit properties and methods from the class to which it belongs
Polymorphism
Stipulates that the same method, if applied to different objects, can produce different effects

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4.4 Topology Rules
Topology introduced in the coverage model but disappeared in the shapefiel model
User-chosen relationship rules
See Table 4.1, page 69

29. 4.5 Advantages of the Geodatabase Data Model
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4.5 Advantages of the Geodatabase Data Model
Take advantage of functionalities from object-oriented technology
Convenient framework for storing and managing GIS data
Eliminates complexity of coordinating between spatial and attribute components of database
Custom objects may be developed