How many types of services are there

The Internet and Internet Services (Lecture)

Priv.-Doz. Dr. Burkhard Kirste
2nd workshop in the project "End-user funding for chemical databases"
Frankfurt am Main, May 19, 1995
  1. What is the internet
  2. Internet services at a glance
  3. Access to the internet
  4. Details on selected internet services
    1. Electronic Mail (email, email)
    2. (anonymous) FTP
    3. World Wide Web (WWW)
  5. Summary

What is the internet

The Internet is a global computer network with 20 to 30 million users. It originated in a network of the United States Department of Defense (ARPAnet) and was then extended to American universities (NSFnet). In the meantime, not only educational institutions but also commercially operated servers are connected worldwide.

It should be noted that only a fraction of the millions of users can fully use all the possibilities of the Internet, since this requires a graphics-capable terminal and sufficiently fast data lines.

Every computer connected directly to the Internet must have a unique one Identifier an Internet address (IP number) and an Internet name. Example:

Internet address Internet name - machine name citral - domain - top-level domain de

The ISO country code is usually used as the "top-level domain", where, for example, "DE" stands for Germany.

Internet services at a glance

The most important internet services are:
  • Email (email, electronic mail, electronic mail)
  • World Wide Web (WWW)
  • Gopher
  • Net News (Usenet News)
  • (anonymous) FTP (File Transfer Protocol)
  • Telnet
  • furthermore: WAIS, Hyper-G, IRC, finger


Email is the "quintessential" Internet service. It is initially used for the direct exchange of information between Internet users and is considerably faster than the "yellow post", but not as direct as a telephone call, but it can also take on the function of an answering machine.

E-mail can also be used to exchange information between larger groups of people via mailing lists, and it can also be used as a replacement for other Internet services such as file transfer (FTP) or the "World Wide Web".

World Wide Web (WWW)

World Wide Web is a worldwide information system based on hypertext documents. Hypertext documents contain references to other documents, which can then be easily reached with a mouse click or a keystroke.

The texts contain formatting features and font attributes and are therefore easy to read. Furthermore, the system is multimedia-capable, i.e. graphics, images, videos and sounds can be transmitted.

It is also easily possible to read WWW documents via a non-graphics-capable text terminal.


Like the WWW, Gopher is also a distributed information system that allows global requests for texts, image data and other files. However, hypertext functionality as in the WWW is not available.

Net News (Usenet News)

The Net News are to a certain extent an extension of the concept of the mailing lists to an international communication service. It is a large discussion forum divided into many different sections, the so-called Newsgroups. These are comparable to the letters to the editor in magazines. Each participant can read the messages and opinions that have been posted there and reply to them with their own suggestions or comments ("post").

Requirements: Access to a computer that subscribes to the "News"; Reading and "posting" software (e.g. nn, tin).

An example of a newsgroup related to the field of chemistry is, or for information systems.

Special call example:

(anonymous) FTP (File Transfer Protocol)

The file transfer protocol or program FTP is used to exchange any files, both text files and binary files, e.g. executable computer programs or image data.

There is a huge amount of such files available on the Internet. Many computer programs are offered free of charge as "public domain" programs; with so-called shareware programs, the author expects a certain financial remuneration after a trial period has expired. Such files can easily be copied from what is known as an "anonymous" FTP server.


Telnet enables interactive work on a remote computer using a terminal emulation. As an information service, it is used in particular to query library catalogs.

Other services

The WAIS (Wide Area Information Server) system is a database system that is used to find information about a computer network.

To a certain extent, Hyper-G is a further development of the world-wide concept. For example, better indexability with forward and backward references is advantageous, disadvantageous are an information structure that is difficult for the user to understand and limited "scalability", i.e. the number of servers that cooperate with one another comes up against practical limits.

IRC (Internet Relay Chat) is a worldwide conference system for "chatting".

"finger" provides some information about Unix workstation users. Information texts can also be called up using a file named.

Access to the internet

At least the computer centers at German universities are connected to the internet via the science network (WIN). University institutes are also increasingly being "wired", ie they are connected via Ethernet or even via a modern high-speed network such as FDDI (Fiber Distributed Data Interface) or ATM (Asynchronous Transfer Mode) via the TCP / IP protocol (Transmission Control Protocol / Internet Protocol) is connected to the campus network and consequently to the Internet.

If a direct network connection is not available, e.g. in the private apartment, you can dial into the Internet via a high-speed modem and the telephone network or via ISDN (Integrated Services Digital Network, 64 Kbit / s) through the intermediary of a network provider. As a university member, you can usually contact the university data center, otherwise one of the numerous commercial network providers.

When accessing via a modem, a distinction must be made between two cases: on the one hand, a simple dial-in via a terminal program into a computer that is in turn connected to the Internet, and on the other hand, a SLIP (Serial Line Internet Protocol) or PPP (Point-to -Point Protocol). In the former case ("Shell Account") one is essentially limited to non-graphic applications, while in the latter case, in principle, full use of the Internet services, including graphic output, is possible. (SLIP and PPP differ in the protocol used, e.g. the type of error correction.)

Documentation and software for connecting a PC (under Windows 3.1) to the data center via SLIP are available for the Freie Universität Berlin area; a transfer to other universities is not possible without further ado.

Details on selected internet services

Electronic Mail (email, email)

Electronic mail, mostly Electronic mail or e-mail called, is used to send letters over computer networks. It is the best-known and most widely used communication service on computer systems, through which tens of millions of participants, especially university members, can be reached worldwide. E-mail offers several advantages over traditional communication using "yellow mail": it is very fast, inexpensive and easy manageable.

Email is not limited to the Internet. There are switching points (Gateways) to other e-mail networks such as BITNET, EAN, CompuServe.

To send an e-mail, you need to know the exact Destination address of the recipient is necessary. The address must be given in a special form; neither typing errors nor omissions are forgiven, and there is no automatic correction.

For example, an Internet email address looks like this:

[email protected]

This address would be the (hypothetical!) User Schulze at a computer in the department physics the Universityuniversity Heidelberg in Dereach utschland. It should be noted that there is no comprehensive directory of Internet mail addresses in Germany. There are only a few partial solutions, such as a list of GDCh members with their email address; Registrations to.

It should be noted that the e-mail system is based on several components: First, that User programwhich is used, among other things, to read and write an e-mail, and secondly Transport program, which takes over the transport and delivery in analogy to the post office (e.g. sendmail, smail), thirdly the Communication protocol between the computers (e.g. SMTP).

An email consists of a header and a body.

To: [email protected] Subject: Meeting on Thursday

The most important headers are "To:" with the address and "Subject:" with a subject. Incoming e-mail contains, among other things, a "From:" line with the sender information.

The body of the text can contain any ("ASCII") text. It should be noted that the use of German umlauts can cause problems, as there are different codings that do not necessarily arrive or are implemented correctly at the recipient.

Typical e-mail user programs have the following scope of performance: selective reading of incoming e-mails, archiving, exporting, printing, answering (reply), Forward (forward) and delete; Write your own emails (compose), possibly using ready-made texts and, if desired, with a copy (Cc :) to other addressees.

E-mail user programs are available for various platforms such as Unix workstations (pine, elm, zmail, xmail), Intel PCs (pmail = Pegasus Mail), Apple Macintosh etc.

Mailing lists

Mail lists are used to exchange information within groups of people with a common area of ​​interest. In order to be able to participate, one must first register with the list administrator, e.g. for the list of project managers in the program "End-user funding for chemical databases":

Informal email to:

[email protected]

Notifications to all participants by email to:

[email protected]

Or the mailing list of the GDCh-Fachgruppe Chemie-Information-Computer (CIC):

Mail to: [email protected] In the main part: subscribe gdch-cic

(anonymous) FTP

The File Transfer Protocol (FTP) is used to transport Files on the Internet. These files can contain programs, data or information texts. That is particularly important anonymous Variant that gives every Internet user access to so-called FTP server allowed. To use them you enter as a user name (User) anonymous or ftp a, your own e-mail address as a password, e.g.

Note that only pure texts like in ASCIIMode can be transferred. Programs (binaries) and all packed archives must be in binaryMode. Packed or compressed archives must then be unpacked or decompressed.

Example of an FTP session:

ftp 220 FTP.FU-Berlin.DE ready, please login as user "ftp". Name ( ftp 331 Anonymous login ok, send your e-mail address as password. Password: [email protected] ftp> cd pub ftp> dir ... ftp> get README ftp> binary ftp> get INDEX.gz ftp> quote site index mosaic ... ftp> help ... ftp > quit

Before fetching large amounts of data from a remote FTP server, you should definitely check whether the file is possibly on a nearby server. To search a service called Archie is recommended for files on FTP servers.

World Wide Web (WWW)

To use the worldwide hypertext information system "World Wide Web" (WWW, W3), you need an Internet connection and a user program, a so-called one Browser. Alternatively, it is also possible to order WWW documents by e-mail or to obtain access via Telnet, see WWW - Getting Started:

Telnet example

telnet login: webinfo

Email example

You have to know the "URL", that is the exact address of the desired document. "send Url"sends the text in ASCII text format," source Url"on the other hand in hypertext source format (HTML).

Send email to:

[email protected] Subject: leave blank; in the main part: send source


In the above-mentioned Telnet example for the Wolfenbüttel University of Applied Sciences, the well-known WWW text mode browser was ultimately used lynx called, which allows the use of this information service via a non-graphics-capable terminal.

WWW became particularly popular thanks to the graphics-capable browser Mosaic; many users nowadays prefer the browser Netscape. In any case, there are now web browsers for all common computer systems such as Unix workstations, Intel PCs and Apple Macintosh.

The use of this information system is basically very easy. To follow a link, you only need to click once on a marked word or symbol with the mouse. The marking is made recognizable, for example, by means of blue coloring and underlining. The jumps are only possible in one direction on the WWW, but the browsers also allow you to jump back to the last document or to navigate within "History" or "Hotlist". The WWW system offers full multimedia support such as graphics, images, sound and video.

WWW basics: HTML and URLs

The "HyperText Markup Language" HTML is used to write hypertext documents. However, this SGML-based document definition only defines the structure of the document. In contrast to PostScript, no specifications are made about the page structure or the fonts to be used. Essentially, these are simply ASCII texts. Formatting features are introduced by so-called "tags", which are always enclosed in angle brackets. For example, the - "Tag" indicates passages that should appear in bold.

The anchors marked with the letter A, with which references are inserted, are of fundamental importance. The link is next to the keyword HREF. As already mentioned, this can be new text, a specific text passage, an image, a sound object or a video clip. The syntax is the same in all cases, the distinction is made on the basis of the file extension; e.g. html, gif, au or mpeg.

In order to be able to clearly address documents worldwide, the concept of the Uniform Resource Locator, or URL for short, was introduced. The URL first specifies the protocol, then the Internet name of the server and finally the file name with the path. WWW servers work with the HTTP protocol, which stands for "HyperText Transfer Protocol". The WWW concept also includes practically all other Internet services such as Gopher, FTP, Telnet and WAIS.

Applications in chemistry

are diverse:
  • Information about the department, institutes and working groups
  • Announcement of lectures and courses
  • Online documentation of software
  • (interactive) teaching materials
  • Electronic publishing
    • Full text with all hypermedia possibilities
    • (only) abstracts
    • Preprints
    • Dissertations?
  • Database research
  • 3D molecular models and spectra via "Chemical MIME"

With the help of the WWW you can disseminate information about an institution such as the Department of Chemistry at Freie Universität Berlin. Lectures can also be announced, such as institute colloquia or the lectures in the GDCh local association.

The WWW is also ideally suited for the online documentation of software. The beginning of the MolScript documentation is shown here as an example. As you can see, graphics or images can be easily integrated, and the texts are much more pleasant to read than e.g. Unix "man pages". Teaching materials on chemistry can also be offered on the WWW, whereby interactive tests can also be carried out with the help of forms or clickable diagrams.

A hotly debated topic at the moment is the field of "electronic publishing". The WWW system is ideally suited for disseminating scientific results without delay. Preprints can be offered on a WWW server; it is most convenient for the reader if the entire document is made available in hypertext format, including images. I already have examples of this from myself, from Henry Rzepa and others. Alternatively, it is also possible to offer only the abstract including a reference to the PostScript document; the document can then be "downloaded" by the reader if necessary.

Chemical Physics magazine, for example, already offers such a preview service. Hypertext abstracts can be read "online" and the full document can be easily "downloaded". The journals J. Am. Chem. Soc. and Chem. Rev. make supplementary material available on the ACS WWW server. Springer-Verlag provides overviews of contents free of charge, preprints for a fee. In the field of mathematics in particular, there are already some real electronic journals.

Of course, this form of "electronic publishing" also raises various questions, such as copyright problems, authenticity of documents, patent law problems and the collection of fees.

In addition to publications, conferences are an important forum for the exchange of scientific information. Here, too, there are already electronic conferences via the WWW.

The possibilities of the WWW are not limited to offering "real" hypertext documents, but with the help of searchable indices, forms and clickable maps, an interactive dialog with the user is possible, which can be used e.g. for database queries.

One example of this is our hazardous substance database for chemicals. In this case we have developed a CGI script and a special database program that provides HTML output with further references. You can get explanations of the R and S sentences when you click on the relevant coding. As a further important example it should be mentioned that there are forms for querying the Brookhaven Protein Database (PDB). The number of library catalogs that can be researched using WWW forms is also gradually increasing; previously there were at best impractical possibilities for this via "Telnet".

Viewers such as "Mosaic" are able to start external viewing programs for various applications. This idea was taken up by Henry Rzepa and expanded to include the needs of chemistry. If you click on a 3D molecular model and the MIME extension is installed correctly, you do not get an enlarged static image, but instead the molecular coordinates are transferred to a molecular graphics program such as "xmol" or "rasmol". In the example it is pinene; the user can now, for example, rotate the molecular model as desired. Animations of reaction processes or molecular vibrations, for example, can also be displayed using "xmol". In the meantime, the idea has also been taken up elsewhere, for example at the University of Oldenburg and the University of Erlangen.

Another extension concerns spectra or chromatograms. For example, it is useful if you can view a section of an NMR spectrum enlarged. A simple enlargement of a section of a pixel graphic is not helpful for this. On the other hand, it makes sense to transfer x, y value pairs to a suitable graphics program such as "xmgr" or "xgraph".


a global computer network with 20 to 30 million subscribers
direct "letter" exchange of information
Mailing lists
Replacement for other services (FTP mail, WWW by mail)
Net News:
Large discussion forum divided into many sections (newsgroups)
interactive work on remote computers
File transfer
"anonymous" FTP server
Archie is used for search
World Wide Web (WWW):
worldwide distributed information system
Hypertext and multimedia support
May 1995: over 23,000 web servers, over 3.6 million web documents

Burkhard Kirste, 1995/05/16