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

CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

CHAPTER 4: OBJECT–BASED VECTOR DATA MODEL Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

4.1 Object-Based Data Model Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Two Differences between Georelational and Object-Based Models Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Two Differences between Georelational and Object-Based Models 1. Stored in single system rather than split

A Land Use Data Set Figure 4.1 Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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.

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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.

Second difference between georelational and object-based data models Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

4.1.1 Classes Set of objects with similar characteristics Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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.

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Figure 4.2 The Geometry property of the Feature class can differentiate the object types of point, line, and polygon.

4.1.2 Relationships Between Classes Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Association How one class may be associated with another Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Aggregation Whole-part relationships between classes Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Aggregation Whole-part relationships between classes One class is a part of another class State is an aggregate of counties

Composition Similar to aggregation The composite owns the parts Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Figure 4.4 An example of type inheritance Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Figure 4.4 An example of type inheritance

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Instantiation Object of one class may be created from objects of another class Figure 4.5 An example of instantiation

Summary 4.1.2 Relationships Between Classes Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

4.2 The Geodatabase Data Model Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

4.2.1 Geometric Representation of Spatial Feature Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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.

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Figure 4.7 A route, shown here as a thicker, gray line, is built on a polyline with linear measures in a geodatabase.

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Feature Classes and Feature Datasets Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. Figure 4.8 In a geodatabase, feature classes can be standalone feature classes or members of a feature dataset.

4.3 Interface Set of externally visible operations of an object Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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)

Interface Encapsulation Inheritance Polymorphism Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

Copyright © The McGraw Hill Companies, Inc Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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

4.5 Advantages of the Geodatabase Data Model Copyright © The McGraw Hill Companies, Inc. Permission required for reproduction or display. 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