As its name shows, Common Gateway Interface, this technology is not a programming language in itself but a set of rules different programs must follow to communicate appropriately. Complying with these rules, any two applications, written in different languages, can exchange data with no inconvenience at all. Thus, we can write CGI script in different languages, the most used ones being Perl and C. They were the first functional scripts included in Web pages and they were mainly used for interaction with user through forms. Through a CGI, a Web page can establish a data-based communication, with which we can read its records, add new ones or change the existing ones. With this technology, we can also create visitor counters, shopping carts, etc.
CGI scripts are usually saved on a special Web server folder, directly located under the root directory, usually called cgi or cgi-bin, and we need special permits from the Web server Administrator to run them. Nowadays they have increasingly fallen in disuse, although Perl has launched new versions to correct previous deficiencies and reboost its use.
Its full name is Actives Server Pages and it is a technology belonging to Microsoft company, based on VBScript (Visual Basic Script) language.
This is a more advanced technology than CGI, although it needs a Microsoft Server to be used (Internet Information Server), or another server where the necessary extensions have been installed, although usually Apache and IPlanet servers do not get on well with this technology (fight among companies?).
Some of its advantages are that it is based on an easily-learned language, that allows for standard access to databases and appropriately managing session and application variables, and among its defects, sometimes these functions are not enough and it needs actual machines.
Servlets and EJBean. Java Server Pages technology was introduced by Sun company, in close collaboration with Netscape, trying to extended Java language functions (created by them) to web-based applications. Since it was introduced, its used has significantly increased, today being one of the technologies most used and required for Web applications. JSP is based on Java language. When Java instructions are included in the pages, they are run on the Web server, returning pure HTML code to the customer browser. They allow access to almost any database and since they are Java-based they are multiplatform, multi-user and have safe code.
JSP is complemented by Servlets. They are programs written in Java hosted on the Web server that are in charge of appropriately managing the access to databases, among many other functions. And they are also complemented by EJBean (Enterprise Java Bean), modules written in Java that can be called from remote machines, converting Web Java language into module language. We will not get into more details about these technologies; there are lots of online manuals you can consult if you are interested. We will just say this technology needs Web servers accepting it to work. It was initially implemented on specific Sun and Netscape servers, but Apache, Resin, etc. are already accepting it and even Microsoft servers have extensions to support it.
Its name comes from Hypertext Preprocessor, and this is a server script language having a very similar syntax to ASP or Perl. It is multiplatform and works both in UNIX servers (apache) and Microsoft servers (IIS), and there are servers specially created for PHP. It is high level interpreted language, run on the server, as the previous ones. It allows access to databases and it is increasingly used in Web applications.
Server Side Include
SSI is a specific language for commands run on the server. We can identify this type of Web site because its extension is shtml. It is supported by most Web servers.
As regards Web servers, the most used ones are the following:
Till now, it is the most used Web server, and it is based on UNIX operating system and mainly intended for it. It is an open code Web server developed by a UNIX programmers’ community, and, what is most important, its standard versions are free. Since it appeared, it has undergone changes to adjust to the current needs and nowadays it supports almost any technology, including JSP, although it does not support ASP without the appropriate extensions.
Internet Information Server is Microsoft Web Server, specially designed to support its own technologies, such as ASP and Front Page extensions. It also has extensions for PHP; SSI, etc.
It is an easy-to-configure server, although it is less safe than Apache. You can find it on the CDs for Windows NT Server, since it is specially intended to work with this operating system, although you can also find an abridged version, called Personal Web Server (PWS) on Windows 98 or Millennium installation CDS, allowing its installation and use with these systems. Although it began from scratch, it is increasingly used and it is gradually gaining territory over Apache servers.
This is a Web server jointly created by Sun Microsystems and Netscape. The latter used to have an own Web server family, Netscape Enterprise, which they adapted to use Java language from Sun, creating what we know as IPlanet server. Specially intended for Web applications based on JSP, Servlets and EJB. Its expansion is now beginning, although for the time being it is very limited to actual uses, since it is not compatible with previous systems. We can also find other Web servers, such as IBM company Server, Resin, etc., but they are less used.
To complete these data, we must mention another set of servers that are needed for many Web applications, such as database servers, that are going to determine what type of database we can handle in our application (Oracle, MySQL, Informix, etc), safe servers, running encoded keys, digital certificates, Securet Socked Layer (https requests), etc. and application servers.
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