Architecture

A scalable geodatabase utilizes a multitier architecture that implements advanced logic and behavior in the application tier (e.g., ArcGIS software) on top of a storage tier (e.g., RDBMS software). The responsibility for managing geographic data in a scalable geodatabase is shared between ArcGIS and the RDBMS software.

Storage in an RDBMS

RDBMSs provide a simple, formal data model for storing and managing information in tables. The schema of a scalable geodatabase is persisted as a collection of tables in the RDBMS where aspects related to data storage and retrieval are implemented as simple tables. Certain aspects of geographic data management, such as disk-based storage, definition of attribute types, query processing, and multiuser transaction processing, are delegated to the RDBMS.

ArcSDE Technology

Prior to ArcGIS 9.2, ESRI sold a core product called ArcSDE: Arc Spatial Database Engine (SDE). At ArcGIS 9.2, ArcSDE is no longer a separate product and is now referred to as ArcSDE technology. It has been integrated into both the ArcGIS Desktop and ArcGIS Server products.

ArcSDE technology serves as the gateway between GIS clients and an RDBMS. It enables users to easily store, access, and manage spatial data within an RDBMS package such as DB2, Informix, Oracle, SQL Server, and SQL Server Express.

ArcSDE technology is critical for users who need to manage long transactions and versioned-based workflows such as

• Managing historical archives
• Distributed editing
• Federated replicas managed across many RDBMS architectures
• Support for multiuser editing environments

The responsibility for defining the specific RDBMS schema used to represent geographic data and for application logic is retained in ArcGIS, which provides the behavior, integrity, and utility of the underlying records.

Geodatabase Application Logic

While the RDBMS manages simple data types and tables and ArcSDE technology enables communication between GIS clients and the RDBMS, additional application logic is required to implement more complex object behavior and integrity constraints.

For example, feature classes, feature datasets, raster catalogs, topologies, networks, terrains, and so forth, are all examples of advanced elements within the geodatabase that are used to implement and model GIS behavior on top of the simple spatial representations stored in an RDBMS. These examples of geodatabase application logic are implemented using a combination of advanced RDBMS functionality and ArcObjects.