About Arc SDE and Application Server

WHAT IS ARCSDE?
ArcSDE acts as the gateway between ArcGIS and your relational database.
ArcSDE is the software that allows you to use the ESRI products like ArcGIS suite (Desktop, Server, and Engine), ArcIMS etc. to store, use, and manage all your GIS data (including feature geometry) in one of the commercial DBMSs like IBM DB2, IBM Informix, Microsoft SQL Server and Oracle.

ArcSDE is a key component in a multiuser GIS because it allows you to “marry” world-class GIS technology with world-class relational database management system technology.

The combination provides you with:

• • Support for concurrent multiuser editing with long transactions, allowing support for many editing andcritical GIS data management work flows.
• • No limits on the size of your spatial database.
• • The ability to serve many concurrent users anywhere on the network or the Internet.
• • The ability to build custom applications from the ArcSDE C and Java application programming interfaces (APIs) as well as ArcGIS, ArcObjects, and ArcIMS.
• • A number of configuration choices.

Why use a DBMS?

Multiuser GIS requires DBMS and comprehensive GIS tools that work with the geographic data.
Using a DBMS is a practical means for sharing and protecting our data investments.
As DBMS capability has evolved into more powerful technology that could support complex data objects, larger queries, and stronger transactional support, the use of DBMS for geographic data management has become much more practical.

ArcSDE provides the flexibility to leverage the capabilities that each DBMS vendor offers so client applications will work the same regardless of what spatial storage method is used.

ArcSDE ensures that full spatial functionality is available regardless of the capabilities in the underlying DBMS. For example, if we build an ArcGIS application using ArcSDE for Oracle, that same application will work if used with ArcSDE for IBM DB2, Informix, or Micosoft SQL Server.

One of the roles of ArcSDE is to deal with the diversity and complexity in the underlying DBMS. ArcSDE is like an “adapter” for client applications to use when they want to store and manage their spatial data in a commercial DBMS.

WHAT IS THE GEODATABASE?

The geodatabase is a data model for representing geographic information using standard relational database
technology. The geodatabase—- short for geographic database -—supports the storage and management of
geographic information in standard relational database management system tables via ArcSDE.

Geodatabases can scale from smaller, single-user databases built on the Microsoft Jet Engine database up to larger work group, department, and enterprise databases accessed by many users. Two types of geodatabase architectures are available: personal geodatabases and multiuser geodatabases.

Personal geodatabases, which are freely available to all  ArcGIS users, use the Microsoft Jet Engine database file structure to persist GIS data in smaller databases. Personal geodatabases are much like file-based workspaces and hold databases up to 2 GB in size. Microsoft Access is used to work with attribute tables in personal geodatabases.

Personal geodatabases are ideal for working with smaller datasets for GIS projects and in small work groups or projects of short duration. Typically, users will employ multiple personal geodatabases for their data collections and access these simultaneously for their GIS work. Personal geodatabases support single-user editing. No concurrent multiuser editing support is provided.  

Multiuser geodatabases are primarily used in a wide range of work groups, departments, and enterprise settings. They take full advantage of their underlying DBMS architectures to support:

• • Extremely large, continuous GIS databases
• • Many simultaneous users
• • Long transactions and versioned work flows that are critical in GIS.

WHAT IS AN APPLICATION SERVER?

ArcSDE is built with client/server architecture—- a client application sends requests to the server. In turn, the server receives the request, generates results, and delivers them to the client.

The ArcSDE server accesses spatial data based on highly efficient spatial search functions, provides geometric data validation, and works within heterogeneous hardware and network environments. Data can be delivered to any client from any server anywhere on a network.

In a typical configuration, an ArcSDE application server resides with your relational database on a server platform. The ArcSDE application server performs spatial searches and sends data that meets the search criteria to the client. For example, a common query handled by the ArcSDE application server is to retrieve all the features in a particular map extent to be drawn in the display window.

ArcSDE sends data to the client using “data buffering”. Buffering is the process of collecting large chunks of data and sending them all to the client application, rather than sending one record at a time. Processing and buffering data on the server is much more efficient than sending all the data across the network and having the client determine which data to send to the end user application. This becomes critical when applications are simultaneously using thousands of records in the database.

ArcSDE uses cooperative processing, which means that data processing occurs on both the client application machine and the server, depending on which is faster. Some functions require no communication with the server. CPU-intensive tasks, such as polygon overlay and clipping, are best performed by the client application to avoid excessive demands on both the server and the available bandwidth.