Enter three-tier architectures, separating presentation from business logic from data. Developers could still use components, but the available components were still largely targeted at UI development. Middle-tier developers were left out in the cold. The Web is beginning to change that. Originally conceived as a two-tier system, demands for dynamic content quickly turned it into a three-tier system.
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Also, because CGI is portable, applications you wrote for an Apache server could usually run against Netscape or Microsoft servers with little or no porting. CGI programs were the first pieces of Web componentware. Once developers realized what CGI could do, some amazing applications began to appear.
Why was this a good thing? There were three reasons. First, the client—a Web browser—was virtually universal. Finally, you could administer all that code centrally.
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Needless to say, all the Active Platform's parallel architectures enable high component mobility from client to server. To fix that, we enter the present ActiveX and future JavaBeans of server components. They also enabled more kinds of Web components. MTS handles all the management of sharing, processes, and threads. All the components that make up an application can share these resource pools.
By itself, it manages a pool of threads and a file cache on behalf of multiple services: the ences.
Web server, news server, and FTP server. Java began as a platform-independent language for creating client-side applets that run inside your Web browser.
Release 1. Of course, JavaSoft also has a component model called JavaBeans. Enterprise JavaBeans provide a high layer of abstraction as well as features suited to multiuser execution. Support, however, appears to be strong, and the specification is moving quickly it should be available during this quarter. If all goes well, Enterprise JavaBeans could be a good server-side component solution, especially for heterogeneous environments. According to sources at both, however, they seem to be leaning heavily toward some kind of adoption of the JavaBeans model. Having easy access to both local and remote services means that more jobs will involve multiple, geographically spread- out resources.
The mainframe world has learned how to deal with this issue by deploying TP monitors. Message-queue managers e. One application sends a message to another by placing it into a queue. It can then continue processing without waiting for a reply. The queue manager guarantees that the message will be delivered once and once only, so if any link fails, any queued messages will be sent once it is restored. Big strides are being made toward this goal.
The product does automatic load balancing, security, thread management, connection pooling, and component management. Now that MTS is being integrated into NT, it defines the programming model for building business applications in Windows. Java Web Server is written entirely in Java. These small Java components can do any job a CGI script can do, often doing it with lower invocation overhead and fewer resources. And even though Java is interpreted, execution speed is not a problem for many server-side tasks. Perl is interpreted, too.
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Native Java compilers such as Asymetrix's promise to remove performance as an issue entirely. Also, Netscape Enterprise Server 3. I t plays hard. ViewSonic monitors have again ken enthusiastically received by distinguished industry reviewer;. PC World calls it " To make any ActiveX component transactional, a programmer need only set its transactional property to Transaction Required and then call one of the API routines Set- Complete or SetAbort at a point in the code where the transaction should either be complete or have failed.
In other words, MTS is not just about financial transactions. Conventional distributed object systems store all data inside objects and maintain long- lived references to them. There are some downsides. That makes it the de facto standard in electronic commerce for software, too. For More Information Call us at , email us at info u globetrotter.
Most vendors are still at the stage of selling ORBs. Many smaller developers are not prepared to wait and are settling for simpler solutions based on ActiveX or Java. Fortunately, there are some powerful tools to help do this.
Load balancing and the ability to group these objects onto a single physical server and move them around are going to be very critical to seal- ability. However, more elegant solutions abound.
Business Object Components
Enroll me as a member of the CPBS according to the terms outlined in this ad. If not satisfied. If you want another book, or no book at all. Purchase 2 more books during the next 12 months, aftci which you may caned your membership at any time. AI books are softcovcr unless otherwise noted. Box Valid for new members only, subject to acceptance by CP8S. Canada must remit in U. For example, tax calculation is a well- known problem. So is currency conversion. Why should you waste your time reinventing these wheels?
On top of that lie the common business objects e. On top of all that lie commercial applications. It depends on which level you're developing for. There are still some problems with writing business applications in Java. If they are in the same process, they can call each other via pointers. This is the basis of ActiveX. JavaBeans can also run as applets outside any container application, and Java Class Loaders can download any libraries a component needs along with the component.
By what mechanism can anyone manage that mess? Right now, the answer is none. But you have to start somewhere.
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Which architecture do you adopt? For example, Java servlets are a very good choice for those applications that might now be done by CGI scripts, such as reformatting tables retrieved from a database. The investment is small, so you just throw them away and rewrite them as requirements change. To some extent, your decision will be affected by the market in shrink-wrapped components.
Here, Microsoft has the advantage of its dedicated band of third- party vendors such as Sheridan and Micro- Help, already experienced in VBXes and OCXes, who are gearing up to produce server-side components. These decisions are rarely mutually exclusive. Each solution has advantages not currently otherwise available.
You can reach him at jmontgomery bix. COM provides a standard way for objects to pass pointers locally or over networks. By Udo Flohr hat could be better than an intranet? And the potential for group work with colleagues all over the globe is limitless. Really, the only flaw is that your intranet can be utter chaos from Day One—until you realize you have to start managing content and controlling access.
Related Business Objects: Delivering Cooperative Objects for Client-Server (IBM McGraw-Hill Series)
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