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Beyond the green screen Traditional host-access vendors boost their product lines to bring on the Web.
We know, we know. Age of the Internet, downsizing and (yawn) 70% of our data is still sitting on IBM mainframes, blah, blah, blah. We know! The question is: What are vendors doing about helping you get at that data? When the issue was just how to get from the desktop on an isolated LAN to legacy hosts, things were bad enough - installing terminal emulation software on each PC was expensive and time-consuming. But an even greater need to connect to legacy hosts is appearing. Now it isn't only the desktops on intranets that need to get to the mainframes. Serving extranet and Internet clients with host data is potentially the foundation for many organizations' World Wide Web presence - with all the security issues that raises. Actually, things only look more complicated. Over the past couple of years, Web-to-host connectivity has evolved into a sophisticated market, and vendors are making the problem of getting access to host applications from browsers much easier than it used to be.On the host or in the rawIBM offers the most obvious way for Web clients to access legacy hosts: It is putting a Web server on the mainframe. IBM also plans to offer a range of "connectors" to link Web applications written in Java to databases such as DB2 and IMS. It will do this using its WebSphere application server and development tools. However, this is all about databases and won't do anything for accessing data served by host applications. IBM's Web-to-host plans extend beyond the mainframe, too. IBM's CICS Internet Gateway, which runs on any Web server under AIX, OS/2 or Windows NT, uses the CICS External Presentation Interface of the CICS Client software that's long been used for traditional CICS access. The CICS Client requests ICS 3270 data from a host, and the gateway maps it to HTML. The gateway then sends the HTML data to the Web server through the server's Common Gateway Interface and then back to the client. This method makes a Web browser look as if it were a 3270 terminal but with a rather more appealing interface. And it does so without having to alter or recompile the CICS programs. The technique, called HTML mapping, is also used by other traditional host-access vendors, including Attachmate and Wall Data. When the mapping is to pure HTML, even the most basic browsers on the thinnest clients can access host data. This is an ideal solution if you have to accommodate users on old, low-powered PCs. The downside of the technique is that host access is not in real time, so you can't support features such as cursor control and macros. These limitations restrict HTML mapping to applications such as simple data entry and database look-up.More than green screensIBM provides a more sophisticated way of accessing host applications over SNA via its Host On-Demand terminal emulation software. The Host On-Demand Java applet works with SNA-to-TN gateways and provides TN3270, TN5250 and VT52/100/220 emulation. A host session starts when the browser follows a link that downloads the Host On-Demand applet from a Web server. You determine if the Host On-Demand Java classes are fully or partially downloaded from the host or reloaded from persistent cache on the client. Whether the Java classes are fully or partially loaded affects how long it takes for the host access to start working. You also set the server with other configuration details, such as where the classes are located and to which hosts to connect. Attachmate and Wall Data use similar approaches in HostView and Cyberprise, respectively. However, these vendors also offer Microsoft ActiveX versions of the client terminal emulator. Which version you use will depend on vendor preference and browser choice (Netscape Navigator users will require Java applets, whereas users of Microsoft's Internet Explorer may choose either). IBM's lack of an ActiveX component is due to its Java commitment and competitive issues with Microsoft. OpenConnect's OC://WebConnect Pro provides the same client services but uses a custom server to front-end the host screen management and translation for the browser-resident components. The intention is to offload at least part of the processing required at the client. Now you have real-time access and all of the other features of 3270 or 5250 terminals. But all you've got are green screens via terminal emulation or HTML interpretations of green screens. What more can you do with the Web-to-host access?Even moreAnother thing you can do is modify the presentation through a technique called screen-scraping. Screen-scraping is the process of creating a representation of a host screen in memory and moving data into and out of fields in the virtualized screen. In effect, this simulates a user's actions. With screen-scraping, the screen fields are presented in a graphical user interface (GUI) that could possibly be enhanced with graphics and data from other sources before and after the user interacts with the display. This powerful technique can revitalize host applications by making them easier to use or by combining their screen data with data from other sources. Host On-Demand doesn't include tools for customizing the GUI in this manner. If you're an IBM customer and want to do this type of screen-scraping, you'll have to get Advanced Transition Technologies' ResQNet for Host On-Demand. Because Host On-Demand complies with the JavaBeans specification for reusable Java components, ResQNet is able to modify and extend the applet. ResQNet allows font specification, color customization, function key buttons, macros linked to specific fields through buttons, function key remapping and field repositioning. Attachmate, OpenConnect and Wall Data offer similar features. Attachmate uses Microsoft's Visual InterDev and Visual Basic to create GUI-ized screens, while Wall Data uses JavaScript, VBScript and HTML. OpenConnect offers a proprietary graphical editing tool called OpenVista and for really sophisticated customization uses Tool Control Language. Most Web-to-host products also support Secure Sockets Layer connections to SSL-enabled Web servers or TN servers. An exception is OC://WebConnect, which uses a proprietary encrypted protocol between the server and client. OpenConnect claims it has optimized this protocol for efficient bandwidth usage, but you would be unlikely to notice this in all but the most heavily loaded networks Of course, you'll also want to evaluate how these Web-to-host tools impact performance. As with any complex client/server system, much depends on component choice and loading. In general, the products will usually meet or exceed host-access performance provided that the Web-to-host components are running on adequately powerful hardware (typically at least a 200-MHz Pentium with a minimum of 64M bytes of RAM). In fact, many of the performance problems will result from limitations of the host gateway server. An interesting issue of these solutions is that although they solve the Web-to-host problem, they have the side effect of removing the immediate need to migrate applications and data from hosts to intranet servers. And of course the pragmatic nature of IT groups tends to prefer to leave well enough alone. That 70% of corporate data on legacy hosts is going to be around for a long time. |
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 Web-to-host picks
Wall Data, Kirkland, Wash.
Attachmate, Bellevue, Wash.
IBM
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