Object-Oriented Data Model: An Introduction

Prior to this release, ArcInfo was solely based on the highly successful georelational data model. This geometry-centered model focuses on point, line, and polygon geometry types, storing geometry and topology in binary files and associated attributes in a DBMS. ArcInfo 8 continues to support the full georelational data model.

In addition, ArcInfo 8 also introduces a new object-oriented data model for the creation of intelligent "geodatabases" that combine the properties of objects with their behavior. ArcInfo implements objects in a modern and standard way. Each object is defined as a separate component or building block. This allows users to create their own object-oriented models that extend the base model. Object-oriented data models closely resemble the user's own view and classification of the things they study. These data models are therefore intuitive and simple to use--the software will deal with user-oriented concepts like land parcels and easements, transformers and fuses, not system-oriented concepts like points, lines, and polygons.

One of the implications of the geodatabases is that GIS will be more extendable by users and third party developers. New components can be easily plugged into the system and anyone proficient in modern programming techniques will be able to create first class objects. Standards mean better use of well established tools such as programming languages, computer-aided software engineering (CASE) tools, and databases; they also mean openness and interoperability. The new ArcInfo 8 applications have been designed specifically to work with this object-oriented data model.

The ArcInfo 8 object-oriented data model facilitates important tasks including

• Editing a heterogeneous set of features such as points and lines
  
• Modeling complex network features such as devices on a network that have internal circuitry represented by discrete features
  
• Representing a feature's geometry with parametric curves such as circular arcs and Bezier curves
  
• Representing features in multiple ways in the core software (e.g., the generic draw methods of city objects could represent them as red points at 1:500,000 scale, and orange polygons at 1:50,000)
  
• Managing a versioned database that supports work order management and many simultaneous edits
  

Object and Relational Views of the Geodatabase
The geodatabase model supports an object-oriented vector data model. In this model, entities are represented as object with properties, behavior, and relationships. Support for a variety of different geographic object types is built into the system. These object types include simple objects, geographic features (objects with location), network features (objects with geometric integration with other features), annotation features, and other more specialized feature types. The model allows you to define relationships between objects, together with rules for maintaining the referential integrity between objects.

ArcInfo 8 supports two views of this data model: the object view and the relational view. The object view of the database is used by the new ArcInfo applications to define and work with the database as an integrated network of geographic objects. The relational view provides a simpler, nonobject view of the data model. The relational model corresponds to the "simple feature" model used in ArcView GIS, MapObjects, Oracle Spatial, and other systems and standards (such as OGIS simple features and SQL/3 spatial). This means that software and applications that understand georelational data (i.e., ArcView GIS 3.x, ARCPLOT, MapObjects, etc.) can view and make use of geodatabases.

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