Internet Technology Overview (SAP Library - Network Integration Guide (BC-NET))

Internet Technology Overview

The term "Internet" is used in a variety of meanings. Strictly speaking, the Internet results from the connection of many smaller networks, which are operated by a variety of organizations, to form one large network. This means that there is only one Internet. It was founded as a research project by the US Department of Defense, and subsequently expanded to include international research institutions and universities. In recent years it has become a public, worldwide, and increasingly economically oriented network with unlimited access for both business and private users.

Internet Protocol (IP) Network Technologies

All participants in the Internet communicate using standard networking technologies based on the Internet Protocol (IP). These standards are publicly available and are continuously developed by specialists in the field. They are thus called "open standards".

The World Wide Web

One of these standards is the World Wide Web technology, abbreviated as "WWW" or "Web" technology. It lets the user retrieve different materials over the network, including textual information and multimedia content. These materials are retrieved from different sources in a uniform way by using a Web browser. Using additional software, such as the SAP Internet Transaction Server, a Web browser can also enable you to perform interactive transactions on the Internet.

The Web is the part of the Internet that is accessed through Web browser technology. E-mail technology is an example of a different Internet technology. Often the terms "Internet" and "Web technology" are used synonymously. The phrase "connecting SAP to the Internet" in this sense means "building a Web interface for SAP".

Some other terms that are used frequently in this context should also be mentioned. An "intranet" is a corporate network, which is not necessarily connected to the Internet. By setting up an intranet, a company uses the open networking technology of the Internet internally, to connect its different branches or subsidiaries. The intranet thus offers a World Wide Web service to internal users. An extranet is usually a network that connects different companies for business purposes, but that is restricted to a defined set of partners and not publicly available. Many companies use the Internet, intranets and extranets: the Internet for public information about the corporate and shopping applications, an extranet to enable communication with external customers or partners, and the intranet to enable communication within the company.

HyperText Markup Language (HTML)

Web pages are retrieved by a Web browser and displayed in a window. The format and contents of a page are determined by the page-description language, HyperText Markup Language (HTML). This language not only forms the content of the text, but also contains formatting instructions, called "tags", to format:

Text characters (such as bold formatting), lists and tables
Links to other Web resources
Images embedded in Web pages
Forms that can be filled out by the user and returned to the Web source (containing text fields, buttons and similar components generally found in graphical user interfaces).

The HyperText Transfer Protocol

The Web server (also called "HTTP server"), is a program that handles Web browser requests (or refers to the machine running such a program). The protocol used for communication between the Web browser and Web server is called HyperText Transfer Protocol (HTTP).

Communication between the Web browser and the Web server is based on a client/server model: The Web browser opens a connection to the Web server and sends a request for a certain Web page. The Web server answers by sending the contents of the page (or an error message). Then the connection is closed. Status information about the connection is not stored. Status information used in complex Web applications (for example, when the user collects items in a virtual shopping basket) requires an additional program for the Web server.

Encryption

Data is normally transmitted in HTTP in non-encrypted text. If the data is sensitive, containing, for example, credit card numbers, medical records, user IDs or passwords, it should be encrypted. Secure Socket Layer (SSL) is the encryption protocol supported by most modern Web browsers and professional Web servers. The SSL-encrypted HTTP transmission protocol is called HTTPS.

Web Resources

A Uniform Resource Locator (URL) is used to specify resources on the Web. The URL contains the address of the Web server, the name of the resource, and the transmission protocol. The structure of a URL is:

protocol://address/name

For example: http://www.sap.com/internet/index.htm . In this example, the protocol is HTTP. The address – www.sap.com – is the IP address of the central SAP Web server. The name of the resource is internet/index.htm , which is the name of a specific file on that server.

Web resources can include:

Static Web pages

Images, sounds and other multimedia data, in data formats known as Multipurpose Internet Mail Extensions (MIME).

Dynamic Web pages that are generated online, for example by a database or an SAP System.

Static Web Pages

In the early days of the Web, the user could only retrieve static HTML pages that had already been compiled in a file before retrieval. Examples of static pages include product information, catalogues, and telephone lists. Static information can be updated frequently, but this requires considerable administrative effort. Instead of static Web pages, you can use a special program to generate Web pages as required. Interactive applications are not possible using static pages. Today, however, you can create (dynamic) Web pages to meet your needs. To do this, you usually need additional software on the server.

The Common Gateway Interface (CGI)

One method that enables a Web user to access dynamically generated pages uses the Common Gateway Interface (CGI) to connect the Web server to an additional program, which generates Web pages dynamically in response to user input. CGI programs or scripts can manipulate database data and other external information. They are programmed either in a compiled language such as C or C++ (CGI programs) or in a scripting language such as Perl (CGI scripts).

The CGI determines how:

Parameters of user requests are encoded in a URL
User requests are transmitted from the Web server to the gateway program
Data is returned to the Web server

How does the request get to the Web server? HTML forms refer to a certain URL. When the form is submitted by the user, a Web request is sent to the Web server, consisting of the URL and the data contained in the form.

The Web Server is configured to automatically start an external CGI program when certain URLs are called. The CGI program then receives the URL and the form data, performs the required processing and generates the answer page which is returned to the Web server.

CGI Scripts have some disadvantages:

Every new call creates a new process, which has to initialize itself and log on to the database, thereby increasing system load. If there are many calls, performance may be reduced.

HTML pages are generated entirely by the CGI program. That means that every time a change has to be made to page functions or design, a programmer has to alter the program code. This makes complex CGI applications hard to manage.

Modern Web Technology

Many concepts have evolved to overcome the disadvantages of CGI and build powerful Web applications:

Closer Integration of Web Server and Extension Program
All modern Web Servers support advanced extension interfaces that overcome most of the problems of CGI. Unfortunately there is no single standard that all Web Servers adhere to. Two widely used standards are Microsoft's Internet Server API (ISAPI) and Netscape's Netscape Server API (NSAPI). They work as follows: The extension consists of a dynamic library (DLL) or shared object library that implements the API of the server. When the appropriate URL is called for the first time the Web server loads the object into its own process space and passes the request to a function in the object. This function processes the request and passes the response back to the Web server. Subsequent requests are handled much more efficiently because the object is kept in memory.

Web Servers with Integrated Programming Environment
Web server capabilities can be extended by integrating a scripting language into the Web server. In this way, pieces of script code can be embedded into HTML pages. The code is usually marked with a special tag and executed by the Web server before the page is transmitted back to the user. An example is Microsoft's Active Server Pages (ASP). Web applications can be implemented with server scripts that may also access additional data sources, such as a database or an SAP System.

Multi-Tier Web Application Servers
Web application servers are an additional software layer for connecting the Web server with a back end system such as an SAP System or a database. They handle Web requests, user sessions and communication with the back end. The SAP Internet Transaction Server falls into this category.

The Evolution of Web Applications

Since the Web was originally designed for information exchange among scientists, everything started with simple access to static Web pages. The next steps to increase interactivity were search engines and simple database access. The latest step is the complete integration of business processes with the Web technology. The following diagram shows the evolution of Web applications: