机械设计类外文参考文献及翻译 第6页
Server is a better platform for running business application. Better SMP scalability, improved networking performance, and support for more physical memory have a profound impact on the performance of Windows 2000 Advanced Server in an application server environment. Hence, we select Windows 2000 Advanced Server as the operating systemof the running platform. Web Servers including Apache, IIS, iPlanet, CERN, and IBM WebSphere, are frequently installed websites at the present time. Internet Information Services (IIS) 5.0 which is integratedWindows Advanced 2000 Server is a new release Web Server of Microsoft Company. Not only being a Server, it also provides a number of other Internet services such as FTP, News, WWW, and SMTP, etc. With tighter integration between the operating system and IIS, it offers performance gains and higher availability for Web Servers and sites. Normally IIS can not execute Servlet and Java Server Pages (JSP), configuring IIS to use Tomcat redirector plugin will let IIS send Servlet, and JSP requests to Tomcat (and thisway, serve them to clients). Tomcat3.2 of the Apache Software Foundation is selected to act as the engine of JSP and Servlets. Database Server adopts SQL Server 2000 Relational Database. Exchange Server 5.5 is to be used to implement the mail service function. In order to prevent hacking system, two firewalls based on package filtration and proxy Server, namely, Cisico2511 router and Proxy Server 2.0, have been established. The overall configuration of Web platform is shown in Table 1.
6. Design of internet application
6.1. Browse/server model
The model of information service based on WWW falls into two broad categories: Client/Server (abbreviation C/S) and Browser/Server (B/S). C/S is a twotier model where a connection is built directly between the Client and Database Server. In comparison, B/S is a three-tier model where a connection is built between the Servlet or Application Server and Database Server, and the Clients obtain the data from the Servlet or Application Server. In the three-tier model, it is the middle tier of Servlet or Application Server objects that deal with all Database access operations. B/S has the same benefits (e.g. highly interactive, graphical user interface aids productivity) as C/S, but avoids the enormous distribution and maintenance problem. Besides an operating system and personal productivity software, the only software that the user-end needs, is a Web Browser that can run Java Applets. The B/S architecture allows developing professionals to focus on development and maintenance tasks on the Server side in spite of the increasing number of distributed customers. Therefore, there are a number of advantages for a B/S model: thin Client (platform independent), central software storage and control, high interactivity, economy in system development, maintenance and upgrade. Due to the distributed and heterogeneous nature of clients and collaborative enterprises, this service system is based on B/S structure which can fit the distributed and heterogeneous environment of networked manufacturing. The structure of B/S model is shown in Fig. 6.
6.2. Choosing a server-side language
Creating dynamic Web pages that interact with the user showing customized information is the pith of Web application for B/S model. With the rapid development and prevalence of Internet, a variety of solutions have appeared which enables the development of Web application to become more and more simple, convenient and effective. Four Server-side scripting languages including Common Gateway Interface (CGI), Active Server Pages (ASP), Person Home Pages (PHP), and Java Server Pages (JSP), are frequently used now.
CGI scripts are inefficient and difficult to be used for writing Server extensions. Each time someone hits a CGI script, a new process is created on the Server; if a script is written in an interpreted language like Perl, the Server has to start up another Perl interpreter, consuming more processing time and memory. The situation gets even worsewhen it resides on a site that is getting a few thousand hits a day. Another disadvantage with CGI is that a CGI program can not interact with the Web Server during its execution because it is running in a separate process. Microsoft attempted to change all this when they introduced Active Server Pages, which allows developers to use simple scripting to access the Server and its extensions. ASP is almost as efficient as writing code directly to the Server’s application program interface, and it is more efficient than CGI because it runs as a service and can take advantage of multithreaded architectures. But while ASP provides an efficient way to return dynamic content, it essentiallylimits one to Microsoft platforms, and even the
simplest of scripting mistakes can crash or hang the Web Server [41]. PHP is an open-source Server-side scripting language for creating dynamicWeb pages for Web applications. A particular strength is that
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