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Choosing ArcIMS Connectors and Viewers
by Scott Steigerwald, Idea Integration

One of the first questions that comes up when planning an ArcIMS strategy is "Which client should we implement?" This can be a difficult question to answer. Esri provides three viewer choices. However, the choice of connector--the Servlet, ActiveX, ColdFusion, or AppServerLink Connectors--can have a dramatic effect on the client side and should be considered when choosing a viewer. The following discussion will help ArcIMS users, developers, and managers decide the most suitable connector and viewer combination.

ArcIMS Clientside Components

Viewers determine the functionality and graphic look of an ArcIMS Web site and offer tools for viewing and querying spatial and attribute data. ArcIMS provides three viewer choices.

HTML Viewer

The HTML Viewer, consisting of HTML and JavaScript, must be downloaded to the client. While this client is thinner than either of the Java Viewers, it is not the thinnest viewer. Thin or thick describes the amount of data downloaded to the browser.

The HTML Viewer's robust functionality is one of the most compelling reasons to use it. This functionality can be extended using a combination of Dynamic HTML (DHTML), JavaScript, XML, and other technologies. Active Server Pages, ColdFusion, and Java can also be used with the HTML Viewer without using the connectors. However, the HTML Viewer supports only Image MapServices. Image MapServices send a snapshot of the data in JPG, TIF, or PNG format to the client-the data is not streamed as with Feature MapServices.

Java Viewers

ArcIMS supplies two Java Viewers. The Java Custom Viewer uses Java applets to serve maps and information. A Java applet differs from a Servlet. It runs on the client, not the server, and must be downloaded to the client. Consequently, Java clients are thicker than the other viewers. To view a Web site that uses a Java Viewer, the user must initially download two plug-ins. Both Java Viewers can serve Image and Feature MapServices. Feature MapServices use data streaming, which allows user interaction and analysis.

Neither the tools nor the format of the Java Standard Viewer can be customized. The Java Custom Viewer can be customized through HTML and scripting to the applets using JavaScript. Because Netscape does not support applet scripting, the Java Custom Viewer will not work in Netscape browsers.

Application Server Connectors

ArcIMS Application Server Connectors link the Web server to the ArcIMS Application Server. The Servlet Connector-the default connector for ArcIMS-can use all three viewers that come with ArcIMS. The ColdFusion and Active X Connectors use custom clients and translate their own languages into ArcXML to communicate with the ArcIMS Application Server.

Servlet, ColdFusion, or ActiveX Connectors can be used to connect the Web server to the ArcIMS Application Server.

The AppServerLink is a conduit that allows a Java application to send ArcXML requests to the ArcIMS Application Server. It can be used with a Java application, a Java applet embedded in a Web site, or a Web site built using JavaServer Pages (JSP).

Servlet Connector

A Servlet is a Java application that runs on the server. In order for the Servlet to work, a valid Servlet Engine is needed. Some Web servers have native Servlet Engines. Web servers that do not have a native Servlet Engine require a third party Servlet Engine. Servlet Connector Web sites can use almost any combination of Web server and viewer. ArcIMS Designer can be used to create Web sites for the Servlet Connector, and little custom code is needed to create a basic, yet robust, Web site.

ActiveX Connector

With the ActiveX Connector, a site can be developed using Active Server Pages (ASP). VBScript, HTML, JavaScript, and XML can be used to customize a site. ASP are interpreted on the server into browser-readable format-nothing is downloaded to the client. The ActiveX Connector custom client is thinner than the HTML Viewer or either Java Viewer. The ActiveX Connector requires a Microsoft Windows-based server, and the Web server must be Microsoft Internet Information Server (IIS). The client can be any browser, and no plug-in is needed.

The ActiveX Connector can also be used to write Visual Basic (VB) applications independent of the browser in a fashion similar to writing MapObjects applications. Esri provides samples, and an object model is included to support additional development. However, the functionality of VB-customized browsers is not as robust as the HTML or Java Viewers.

ColdFusion Connector

The ColdFusion Connector is very similar to the ActiveX Connector in that ColdFusion code resides on the server and is interpreted into a browser-readable format for the client. ColdFusion uses the ColdFusion Markup Language (CML), a set of HTML-like tags that are interpreted by the ColdFusion Server. This connector can be used on Windows or UNIX servers with most Web servers. The ColdFusion Server must be installed on the Web server. The ColdFusion Connector custom client is thinner than the HTML and Java Viewers, and requires no plug-in. ColdFusion sites can be written using ColdFusion tags, HTML, JavaScript, and XML.

Esri provides samples that can be used to get a site started, but the functionality is not as robust as that of the HTML and Java Viewers. While no object model is provided, an ArcIMS toolbar is added to the ColdFusion development environment, ColdFusion Studio, making it easy to develop applications. ColdFusion Studio should be installed on the machine used to develop applications.

AppServerLink

The AppServerLink provides many options for writing Java-based ArcIMS Viewers. Java applications, applets, and JSP can be created using the AppServerLink. Java applications are written in much the same way that MapObjects applications are created. Like the Java version of ArcExplorer, stand-alone Java applications can serve ArcIMS data and information. Applets can be used to create Web sites similar to sites using the Java Viewers, but this solution provides more customization and control.

Finally, JSP, an extension of Java Servlet technology, can be used with the AppServerLink to create Web sites that work and look like ASP and ColdFusion sites. All code can be written in using JSP and Java, HTML, JavaScript, and XML. The server interprets the code into a browser-readable format.

The AppServLink is a JavaBean, a reusable software component. Its methods allow a programmatic connection with an ArcIMS Application Server.

Another thin client option, JSP can be served to any browser without a plug-in but requires a Servlet Engine on the server. However, because ArcIMS needs a Servlet Engine anyway, no additional resources are necessary. Esri has supplied an API for the Java classes and Java and JSP Viewer samples that implement JavaBeans and use the AppServerLink.

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