The Web technology infrastructure consists of a range of components. The key components are discussed in the following sections.
TCP/IP Network
The Transmission Control Protocol/Internet Protocol (TCP/IP) must be implemented as the standard across the corporate networks. TCP/IP is avail- able for most platforms including UNIX, Windows NT, Windows 95, and Macintosh.
Client Database server Database
Figure 6.1 Two-tier client/server architecture.
Database Database server
Application server Client
Figure 6.2 Three-tier client/server architecture.
Web Server Platform
The most common Web server platforms are UNIX (Sun, IBM, HP, or Digi- tal), Windows NT (Intel, Alpha, or RISC-based machines), and Macintosh. Of course, many factors must be considered when choosing a hardware platform.
The performance capabilities of the computer in terms of the speed of the processor, the amount of random access memory, and disk storage need to be considered. The reputation of the manufacturer for hardware reliability may be a consideration because the server will be running 24 hours a day, 365 days a year. If problems do arise that are hardware and software related, then good quality support is important. The hardware may need faults diagnosed and eventual replacement. Service companies may pick up the hardware, repair it, and return it if it is still under warranty.
The level of compatibility with existing hardware may be a factor for consideration. However, the operating systems cannot be divorced from the hardware platform and so this is just as important a factor. The choice of server platform could also be influenced by the level of expertise within the organiza- tion. There may be expertise, for example, in Windows NT software but very little in UNIX.
Web Server Software
Web server software runs on a computer connected to the Internet. The server software takes requests from Web browsers for HTML documents, locates the document, and returns it to the browser that requested it. Common Web server software includes Apache, CERN, Microsoft IIS, NCSA, and Netscape.
The hardware will determine which software options are a possibility. Much the same factors that are considered for hardware must be considered for soft- ware, including performance, scalability, security, reliability, level of support, level of compatibility, level of expertise, content and site management features, Web development support, and quality of documentation.
Web servers perform four main functions: (1) serving Web pages, (2) running gateway programs and returning their output, (3) controlling access to the server, and (4) monitoring and logging server access statistics.
Web Browser
The choice of Web browser will be influenced by the hardware and operating system platforms within the organization. If several hardware platforms are used, then the browser chosen should be available on all platforms. It is recom- mended that one browser be chosen as the standard because this will make support and training much easier.
If the organization does support different browsers, it is important to test any Web pages developed in all of them. This is because there are differences in the way a page is presented by different browsers.
Web Integrated Development Tools
A range of integrated development tools exists that utilize the Java program- ming language. They are rapid application development tools that have been created to develop Web-based applications in Java. The tools speed devel- opment by providing a visual programming interface that hides some of the complexity of developing low-level components and interface objects.
Java integrated development tools or environments (IDEs), in addition to being used for developing Web-based applications in the form of Java Applets, can be used to develop stand-alone applications that do not require a browser.
Chapter 7 explains the role of Java in developing Web-based applications along with other scripting languages for client-side applications development.
Three of the main Java integrated development tools are described next.
IBM’s VisualAge for Java
IBM’s VisualAge for Java is described as a rapid application development tool for building Java-compatible applications, applets, and JavaBean components.
There are two main versions: the Professional Edition for developing appli- cations, and the Enterprise Edition, which has modules for connecting to databases. Here are some of the features of VisualAge:
• An integrated development environment with visual programming support for creating Java applets;
• Wizards for string externalization to assist in building multilingual applications;
• Ability to import GUIs that have been developed in other Java devel- opment environments;
• JavaBeans for easy access to databases;
• HTML documentation support.
Borland JBuilder
JBuilder includes visual tools and reusable components for developing platform-independent applications, servlets, and applets. Servlets are standard Web server extensions that can be used to expand the functionality of a Web
server. Borland relies on the Java 2 standards set out by Sun Microsystems. It comes in three versions: Standard, Professional, and Enterprise.
Sun’s Java WorkshopTM
Java WorkshopTMis a visual development environment that offers a tool set for building Java applets, applications, and JavaBeansTMarchitecture-based compo- nents. It provides a graphical development environment to speed development.
The Project Manager is a file management utility. The Source Editor provides syntax highlighting, a file picklist, automatic indentation, and key emulation, all of which aid the program development process. The Build Manager is the compiler, which provides automatic error location support for improved debugging. The Graphical Debugger includes controls such as conditional and counted breakpoints, expression and variable evaluation, multithreading sup- port, and visual control of program execution to aid the debugging process.
Version control is incorporated to support team development. Applica- tion performance can be fine-tuned with the Java Workshop Profiler. Wizards are available to help in the development of JavaBeansTM architecture-based components, which are required when connecting to a database server.
Web Database Application Development Tools
Some of the integrated development tools incorporate the modules to connect to various databases. However, they are classed as more general Web develop- ment tools. Specialized Web database development tools have been created to cater specifically to the problems of connecting to databases from Web servers.
However, it could be argued that if a company is considering developing Web- based applications, then it may as well invest in a tool that supports connection to a database. These are termed Java enterprise development tools (EDT). The factors to consider when selecting a Java EDT are shown in Table 6.1.
Several issues must be resolved when connecting to a Web database.
Whereas each ordinary Web page request is processed individually as a com- pletely separate request, this is not the case with database requests. A database request needs to maintain session information or information about the state of the transaction back and forth to the user. This information is embedded in the HTML code. Some systems need to handle a large number of concurrent trans- actions. Some tools can spread the requests over several servers.
Common Gateway Interface
Web servers interact with database servers using the Common Gateway Interface (CGI) method. When a request is made that requires data from the database, a
CGI script is invoked on the Web server. Data is retrieved from the database and then formatted into HTML code. Form-based queries are slightly more complex than document-based queries. A Web page with a form is an HTML file that is on the server. In this respect, there is nothing special about how the Web server or the client browser handles the page. However, when the form has been completed and submitted, the browser sends the name of a CGI script built into the HTML code for the page for the Web server to run. The data input to the form, of course, is also sent to the Web server. The Web server then passes the data to the CGI script. This process is illustrated in Figure 6.3.
Bridging Legacy Systems to the Web
Some organizations are choosing to link their legacy systems to Web interfaces.
The advantages of doing this are:
• A Web interface may be less expensive to develop than rewriting the legacy system.
Table 6.1
Considerations in Selecting Enterprise Java Tool
Factor Significance
Support for recent versions of Java Java 2 has added functionality for enterprise development and hence it is important for the EDT to be compatible with this recent functionality.
Supports standard Java Some IDE and EDT tools have proprietary extensions and class libraries that are not part of Sun’s standard Java. This means there is a danger of being locked into a particular IDE product and vendor.
Version compatibility When the Java platform is upgraded, the IDE should be able to operate with that.
Database access IDEs, especially the enterprise versions, come with the code to connect to databases. This saves time and the acquisition of expertise to do the task.
CORBA support The IDE should support the CORBA object request broker standards.
Component development The IDE should facilitate the development of reusable components.
• The opportunity may arise to exploit new business opportunities by opening up the legacy systems to the Internet.
• Extra functionality may be added at the Web interface rather than making costly changes to the legacy systems.