- Part 3

Preface | Part 1 | Part 2 | Part 3 | Part 4

3. Web Technology

Web technology is an innovative part of modern information and communication technology (ICT). The World Wide Web is an open unstructured hypermedia information system. It is based on flexible linked HTML documents, in which different types of Web objects can be embedded. Interactive components can be integrated beside multi-media objects like images, videos and audio sequence. In this way the World Wide Web provides new possibilities and features for information modeling, analysis, presentation, documentation, exchange and sharing in the net and enables new ways of collaboration between project partners over the Internet as technical backbone.

Web technology has meanwhile a broad distribution in all relevant fields of modern life. The introduction and application of this technology in engineering is an on-going process. Some business sectors use the Web technology already in their daily work. In these sectors the matter of interest (information, products or services) has been standardized and modeled for computer and net application. In disciplines of civil and environmental engineering like hydroengineering this pre-requisite is not yet done. A matter of interest, the water related structures and its behavior in the natural environment is much more difficult to model or even to standardize. The review, adaptation and application of Web technology for hydroengineering is one actual task and scope of the discipline hydroinformatics. The basics of this technology are summarized in this section.

3.1 Evolution of Net Working

The Web technology uses the advantages of the object oriented approach to integrate data, methods and actions in objects. These objects are described by standardized languages, formats and are classified by types. They can be transferred in the Internet using a client/server communication protocol. Main advantage of the Web technology is the platform independence of the Web objects.

First types of Web objects were textual and graphical objects, structured and layouted in documents as HTML pages. Today multi-media objects (e.g. audio, video or 3D worlds) as well as interactive objects (e.g. Java applets) are coming up in Web applications. This object oriented approach enables an overcome of the traditional separating of complex programs and function libraries, large databases and complex textual and graphical documents to a more flexible combination of integrated software modules in the net. This new philosophy of net application is the actual result of an on-going process in net working. Figure 1 describes the evolution of net working in an abstract manner.

First use of the net in the mid-80's was dominated by file transfer for data exchange. One example is the post- and pre-processing at the user's local workstation and the remote simulation/analysis processing on a high performance computer. Another example is the transfer of measurement data files between a meteorological service and a harbour administration office.

At the begin of the 90's the net supports modern window based graphical user interfaces by client/server technology. Events are transferred over the net. An event contains data and action/reactions. Operation systems and user interfaces are window based systems. Example is hydroengineering software with graphical user interface based on X-Window. In this traditional way of computer and network applications all necessary resources, programs and data are on one computer. This could be a PC or workstation on the desk or alternatively on a remote server. The net is used to transfer resources over net and to realize a remote control by events.

The global idea of the Internet leads to a change in the basics of computer science:

`The Network is the Computer' means all the systems work together like one big resource. Sun has always seen our customers' computing needs answered by a variety of computing resources in a heterogeneous network.

Scott G. McNealy, President of SUN Microsystems, April 1987 (really 1987 !!)

Using this philosophy all necessary resources are in the net. The operation system is the Internet, the user interface is the Web with the Web browser as front end. All information and resources are provided by Web servers and transferred as platform independent objects. Objects contain data, actions and methods. The separation of data models and algorithm methods has been overcome. In nowadays XML can be used to add semantic to objects (self-describing objects) towards information. The user can download all necessary information from the net and can provide new information in the net. He can use resources over net such as high computer performance, data storage systems and document archives. This new technology of net application will introduce new innovations in hydroengineering. A new generation of software application on the net is coming up in an on-going process.

3.2 Web Techniques

The World Wide Web is a distributed hypermedia information system. It contains servers which provide services over the Internet and clients requesting for such services. Servers and clients are independent and distributed all over the Internet. Standardization of Web techniques for the server/client interaction are mainly forced by the World Wide Web Consortium W3C, a cooperation of CERN (European Laboratory for Particle Physics, initiator of the World Wide Web: Tim Bernes-Lee 1989), MIT (Massachusetts Institute of Technology, USA), INRIA (Institute National de Recherche en Informatique and Automatique, France) and other commercial and nonprofit partners.

The main technological elements of the World Wide Web such as protocols, addresses and languages are summarized in the next section. Newest information about Web techniques are available on the W3C Server (http://www.w3.org).

3.2.1 Protocols

The communication between servers and clients is realized by communication protocols. The Web browser is the client, the Web server is the server for the communication in the Web. The Hyper Text Transfer Protocol (HTTP) (http://www.w3.org/Protocols) is the client/server communication protocol of the Web as part of the application level (7) of the ISO/OSI network protocol model (http://www.iso.ch). The general concept of HTTP has two steps: a client sends a request to a server, the server answers with a response to the client.

The connection between client and server is installed for each message in both directions for request and response. The connection only exists, when data respective objects are transferred. A HTTP message contains a head and a content. The head includes standard information like the length (Content-Length:), the MIME-type (Content-Type:), title (Title:), date (Last-Modified:) and several other information. Extensions can be added, they are signed by 'X-' like (X-Servermode:). The content is defined by the Web objects to be transferred in the net.

The protocol HTTP defines a representation of the Web objects by different types (called MIME-types: Multimedia Internet Message Extension). Examples for MIME-types are simple text (text/plain) HTML pages (text/html), MPEG Videos (video/mpeg) or postscript documents (application/postscript). The handling of Web objects on the client side can be done by the browser itself (text, html, gif), by plugins (mpeg, vrml) or by external applications (postscript, rtf).

Besides the HTTP protocol other protocols of the ISO/OSI model are used in the World Wide Web. These traditional Internet protocols are extended by new protocols for wireless Web applications like WAP (Wireless Application Protocol) and SMS (Short Message Service) for mobile phones.

3.2.2 Addresses

The location of Web services in the Interent is specified by URL addresses (Universal Resource Locatorhttp://www.w3.org/Addressing/URL) with a typical structure:

protocol://server/path/file

Example for such a URL is the Web address of the homepage of the European Engineering Graduate School Environment Water (EGW) courses at the BTU Cottbus.

http://www.bauinf-tu.cotttbus.de/EGW/Welcome.html

3.2.3 Languages

HTML (Hypertext Markup Language) is the so called language of the World Wide Web. The roots of this language have been developed at the CERN to get a distributed access to simple hyper text documents for a working group. A lot of different HTML variants have been developed over the last years. The W3-Consortium (http://www.w3.org) works on the standardization of HTML. HTML 4.0 is today the actual version, HTML 5.0 based on XML will come soon. Detailed information can be received from the WWW (http://www.w3c.org/MarkUp).

HTML is a 'Content-based Markup Language' based on SGML containing tags to define mark components of a document, their logical structures and their layout properties. Tags also contain links to other WWW resources and are used to integrate non textual Web objects like images, videos or applets. Main HTML features are tags for:

• text (including color, size, font and emphasis features)
• structures (headings, paragraphs, normal lists, numbered lists, definitions)
• tables (row/column oriented layout)
• images (including interactive maps)
• style sheets (generalized property definitions)
• frame sets (structured combination of pages)
• interactive components (such as Java Applets)
• hyperlinks (http and other Internet references)
• scripts (dynamic documents, e.g. JavaScript)
• dialogue forms (input boxes, buttons, labels and other elements)
• accessibility (titles, keywords)
• embedded multi-media objects (video, audio, 3D worlds, applets)

The integration of these and several other features in HTML offers a wide range of Web based applications. It is beyond the topics of this thesis to describe all HTML tags and their applications in detail, but a lot of literature especially in the WWW is available. One outstanding example is SELFHTML written in German (http://www.teamone.de/selfaktuell). Therefore this thesis will not go into more details of HTML.

HTML documents can be edited by several software products. Generally three ways to create and edit HTML files are used:

• ASCII editor
• HTML editor
• HTML converter

HTML files are ASCII-files and can be edited by text editors like vi or emacs. In this way all features of HTML can be used directly. Graphical HTML editors offer a 'What You See Is What You Get' (WYSIWYG) way of editing HTML files. They do not support all non-visible features of HTML. Examples are Netscape Composer and Microsoft FrontEnd. HTML converters generate HTML files for documents of paper oriented documentation systems like Word (Microsoft Office) or Interleaf. These converters can only consider those features which are part of HTML and the paper oriented document formats. There is an ongoing process to integrate WWW features of HTML in standard office packages like StarOffice of Microsoft Office . But there is still a difference between a paper based sequential structured document and a Web based non sequential multi-media document. The result of converters between both media (paper and Web) is mostly not sufficient for high quality presentation.

3.3 Web Basic Software

3.3.1 Web Server

Web servers offer in the Internet different services. Several software solutions are available from different software providers. Some of them are public domain. The progress in this software domain extends too rapidly to describe the actual versions of Web servers. Latest information on commonly used products are available in the net:

• IPlanet Web Server (http://www.iplanet.com)
• Microsoft .net Enterprise Server (http://www.microsoft.com/servers/)
• SUN Java Web Server (http://www.sun.com/software/jwebserver/index.html)
• Apache Server (http://www.apache.org)
• Roxen Server (http://www.roxen.com)

Besides the standard functionality of providing HTML files, Web servers offer several useful services like client access control (via password), administration of several sub domains and security mechanisms for sensitive data exchange (e.g. SSL Secure Socket Layer) and digital signature.

3.3.2 Web Client

The Web browser is the main application software on the client side. The browser sets up the connection to the Web server which services are demanded by the user. The browser receives the Web objects on its request from the server and presents them in a suitable way for the user. The Web browser sends Web objects back to the Web server which have been edited by the user. Examples for Web browsers are:

• Netscape Communicator (http://www.netscape.com)
• Microsoft Internet Explorer (http://www.microsoft.com)
• Sun's HotJava Browser (http://java.sun.com/products/hotjava/index.html)
• Opera (http://www.opera.com)

Web browsers contain several integrated modules. Examples are:

• HTML browser to present Web based documents (HTML files)
• composer to edit HTML pages
• message center to manage emails as well as news from discussion groups
• conference instruments
• JavaScript interpreter
• Java Virtual Machine for Java applet execution

This combination enables the World Wide Web approach to use the Web browser as user interface and the Internet as operation system for Web based software systems.

3.4 Web Services

A lot of different services are available in the Internet to exchange and share information or to communicate world wide. The World Wide Web integrates these services under a common user interface. Main services are:

• print services
• file services
• remote login services
• email services
• news services
• chats and conferences
• document services
• information services
• search machines

Print Service

Print services provide access, management and operation of shared printers in networks for several users. Print jobs are generated on the local computer and send to the print server. The print server manages all print jobs for a printer in a job queue. Mail services are used to response to the client in case of errors or successful performance of the print job.

File Service

File services provide file transfer based on the file transfer protocol (ftp) and file sharing using the network file system (NFS). Files can be exchanged using ASCII mode or binary mode. This service is independent of the content of the files and the computer platform. In this way it can be used for the exchange of software systems, program sources, documents or data files. Files can be shared in a network using shared file systems (logical disks). Shared file systems appear on the user desktop like a local file system. 'Samba' servers are used for platform independent file sharing in heterogeneous networks (UNIX and Windows operation systems).

Remote Login Service

The remote login service provides the possibility to work on a remote computer. Telnet, rsh and ssh offer a shell dialogue for a remote session. The graphical user interface of remote software systems can be presented and handled on the client side using the client/server concept of X-Window in the UNIX world.

Email Service

Email services based on the SMTP protocol provide an exchange of messages between specified persons to communicate over the Internet. An email contains text as well as all kinds of Web objects and as attachment all kinds of files. Most email tools support the HTML format for the mail content in extension to poor ASCII text.

News Service

News services provide an exchange of messages in open discussion groups on common topics of interest. Users can submit emails to a news group as an answer or comment on questions, problems or requests as well as to start new topics by questions.

Chat and Conferencing Service

Chat and conferencing server are meeting points in the Internet. Chat servers (internet Relay Char IRC) offer a live discussion environment based on text exchange. A lot of chat clubs usefully and senseless are available in the Internet. Conferencing servers offer the possibility to connect selected people over the net for video and audio conferencing including application sharing.

Document Service

The exchange of hypertext documents was the root task and is still the main application in the World Wide Web. Web based documents are described as HTML files including or linking all kinds of multi-media presentation and interactive components.

Information Service

The access to information is one key issue of modern life. The WWW provides a new and efficient medium for the exchange of information. Based on Web based documents more and more information are provided by several information providers. One important task for the future is the reduction of this information 'overflow' to valuable information. First existing approaches in this direction are Web communities/portals with specific interest and editorial prepared and structured information boards.

Search Machine

Search machines offer powerful functionality to find information in the WWW based on automatically content analysis and keyword definitions. In addition most search machines provide editorial structured link collections. Well known international search machines are yahoo (http://www.yahoo.com) and altavsita (http://www.altavista.com).

Service Integration

The World Wide Web integrates these different services and offers a powerful information system with graphical user interface, multi-media information presentation, interactive editing and manipulation features, communication and conferencing tools as well as the dynamic adaptation of the information presentation (quantity and quality) by the demands of the user. Especially the active features will give the WWW the benefit in comparison to the traditional information systems like TV, broadcasting, journals and newspaper, which are passive media without user activity.

3.5 Web Multi-Media Objects

Web multi-media objects can be used to get a more comfortable presentation of interesting information. Typical types of multi-media objects used in the WWW are:

• image
• animation
• video
• 3D world

Other multi-media types (e.g. audio sequences) are available in the WWW but have no special application domain in hydroengineering.

3.5.1 Image

Images are no new presentation forms. They have been used in traditional paper documentation as graphics. In the domain of Web based documents images can be handled more flexible. Usual image formats are GIF, TIFF and JPEG. Application examples in hydroengineering are charts, maps, diagrams, sketches as well as photos, satellite images, illustrations or logos. GIF images provide the possibility of transparency and can be used to realize a layer technique. JPEG and TIFF offer powerful compression algorithm to reduce the necessary memory size of an image.

Images can be extended in HTML files for interactive selection functionality by ImageMaps towards interactive images. ImageMaps define regions of the image with a link to other Web objects. In this way the user can get more information by a selection in these regions.

3.5.2 Animation

Animation can be used to present time dependent processes in two dimensional visualizations. An animated GIF image is a sequence of static GIF images which can be played with a fixed time step. They can be used for a two dimensional visualization of instationary processes like current and wave propagation or transport processes. Animated GIF images are directly supported by Web browsers.

3.5.3 Video

Videos are movies, digitally stored in computers mostly combined with audio sequences. Videos can be embedded in Web based documents and played with standard video players. These players can be external programs as well as plugin components of Web browsers. Typical video formats for the WWW are MPEG and AVI. Video objects can be used in hydroengineering for field observation as well as for animations.

3.5.4 3D World

3D worlds are presentations of geometric and physical models by 3D objects. The 3D objects can contain dynamic (time depending) behavior. VRML (http://www.vrml.org) is the usual format for 3D worlds. The projection control of the 3D worlds in a Web browser is done by a plugin tool (e.g. Cosmo Player http://www.cosmosoftware.com). This tool enables the user to control the dynamic behavior of the 3D world and to navigate in the 3D world. In this way VRML objects provide a real interactive dynamic 3D world for virtual reality application.

3.6 Web based Application Techniques

Web based applications are software components which run in the Internet. They can be offered by Web servers to transfer over the net or they are installed on the client side. Main types of Web based application techniques are:

• CGI
• JavaScript
• Java applets and servlets
• JavaServer Pages, Active Server Pages and PHP
• ActiveX
• Plugin
• external application

3.6.1 CGI

Common Gateway Interface (CGI http://www.w3c.org/pub/WWW/CGI) is a standard interface to call small programs on the server side from the client side independent of the implementation techniques. The client can call these programs with parameters as request and get back the answer of the program as response. CGI programs can be realized in several programming languages such as perl, C/C++, TCL or shell scripts. Example is an interactive form as HTML file to ask for available data sets in a data base. The HTML form tags include name and server address of the CGI program. The user input is send as post request to the server. The CGI program is started via CGI interface. The CGI program responds HTML tags with the description of the requested data sets.

3.6.2 JavaScript

JavaScript (http://www.javascript.com) is an object based scripting language for dynamic HTML files. These files contain functions to process user input and to generate new HTML output for presentation. JavaScript can be used on the client and on the server side, commonly used on the client side. In this case the statements are part of a HTML file, transferred over the net to a Web browser. The browser executes the JavaScript statements as interpreter. This way allows the dynamic adaptation of the HTML content during execution by generation of new HTML and JavaScript statements. The statements have access to the object structure of the Web browser. This allows an interactive management and editing of the document structure.

3.6.3 Java Applet

Java applets (http://www.javasoft.com) are platform independent programs embedded in HTML documents and stored/provided by a Web server. When a Web browser requests a HTML page with embedded Java applet, the HTML page and the Java applet are transferred over net. The Java applet will run on the client side. Java applets are platform independent using a virtual machine inside the browser as 'hardware' platform. The virtual machine is part of the Web browser and realizes the transformation of virtual machine statements to the real existing processor environment.

3.6.4 Java Servlet

Java servlets (http://java.sun.com/products/servlet) are the corresponding partners to Java applets on the server side. They are located and running on a Web server offering services to Web applications. Interactive elements in HTML pages are forms and applets and can contact servlets to get information or services from the remote server. The Java technology provides with the combination of applets and servlets a powerful environment to develop platform independent client/server applications in the Internet.

3.6.5 JavaServer Pages, Active Server Pages and PHP

The JavaServer Pages (JSP http://java.sun.com/products/servlet) technology provides a simplified, fast way to create Web pages that display dynamically generated content. JSP technology was designed to make it easier and faster to build Web based applications that work with a wide variety of Web servers, application servers, browsers and development tools. JavaServer Pages technology separates the user interface from content generation enabling designers to change the overall page layout without altering the underlying dynamic content. JavaServer Pages technology uses XML-like tags and scriptlets written in the Java programming language to encapsulate the logic that generates the content for the page. Additionally, the application logic can reside in server based resources which the page accesses with these tags and scriptlets. Any and all formatting (HTML or XML) tags are passed directly back to the response page. JavaServer Pages are an extension of the Java Servlet API.

Active Server Pages (ASP http://www.microsoft.com) are the corresponding technology of the Microsoft Corp. developed for the Internet Server of the 'Windows' operation system family. Active Server Pages have an open, compile free application environment to combine HTML, scripts and reusable ActiveX server components to create dynamic and powerful Web based business solutions.

PHP (Hypertext Preprocessor http://www.php.net) is a server-side scripting language, embedded in HTML pages. PHP contains typical programming statements and special statements for data base access in the World Wide Web.

3.6.6 ActiveX

ActiveX (http://www.activex.org) is a special development for the 'Windows' operation systems and part of the COM (Component Object Model) technology of Microsoft. COM is a software architecture that allows to compose applications from different binary software component. AxtiveX is the integration of several standard technologies like OLE (object linking embedding) and OCX (OLE control) for the operation systems Windows 95/98/NT and Windows 2000. ActiveX containers are used to combine ActiveX components to applications. Examples for such ActiveX containers are the software environment of Visual BASIC and important for the WWW the Web browser Internet Explorer (http://www.microsoft.com). Because of this limitation ActiveX is not platform independent, nevertheless Microsoft provides the Internet Explorer in an older version also for UNIX platforms. Newest development is the Microsoft .NET (http://www.microsoft.com/net) as Web based software development platform but this is still not platform independent (company strategy).

3.6.7 Plugin

Plugin software are extensions of Web browsers and run as part of the browsers. Plugins are installed on the local client machine of a Web browser. A plugin will be not transferred over net. Plugins are designed to handle Web objects of one special type which is defined by a file suffix as MIME type in the HTTP protocol. When receiving a Web object with a MIME type linked to a plugin, the Web browser will call the plugin to handle this object inside the windows of the browser. Example for a plugin is the COSMO player (http://www.cosmosoftware.com) for 3D worlds in VRML.

3.6.8 External Application

External applications are all kinds of traditional software independent from Web technology. They are mostly platform dependent and not running over net. They can be easily integrated in a Web environment, using the MIME-type specification of a Web browser. Application data files with specific formats can be offered by Web server. On client request, the data files are transferred over net to the Web browser classified by the specific MIME type for the external application. The browser starts the external application on the client computer by system call with the data file as parameter. In this way the external application can be handled in the Web environment. Nevertheless, the application has to be installed on the client computer and cannot be transferred over net on demand. Examples for the integration of external application are the Acrobat Reader (http://www.adobe.com) for PDF documents and Word 2000 for Word documents.

3.7 Web based Documents

The World Wide Web offers a new kind of documentation for engineering. Web based documents have fundamental different properties in comparison with paper based documents. The application of Web based documents in engineering demands a carefully analysis of the properties and features for documentation, a suitable implementation concept and corresponding new reading and writing methods.

3.7.1 Document Properties

Web technology for documentation was first used by text oriented systems, so called hyper text systems, still used for tutorials, user guides and help desks. They introduce net-based structures in documents. With the integration of dynamic and interactive functionality and multi-media presentation new kind of documents will change the way of information exchange, collaboration and documentation. Web based documents will be one core issue of a new 'Technical Culture' which is fundamental based on the ability of the society on authoring, editing and reading such new kind of documents. Web based and paper based documents can be described and compared:

Table 1: Paper and Web based Documents

3.7.2 Technological Concept

Web based documents use different technological concepts as combination of available Web techniques. One possible combination of Web techniques for Web based dynamic interactive multi-media documents could be:

• language: HTML
• distribution: Web server
• frond end tool: Web browser
• non sequential HTML links
• presentation multi-media objects
• dynamic HTML integrated functionality by JavaScript
• interactive embedded interactive components by Java applets
• interaction connections to server by Java servlets

These Web techniques have to be integrated towards the needs of documents in hydroengineering. One typical concept is presented in Figure 8. Other combinations are also possible.

The core of a Web based document is its structure described in HTML. This structure defines the integrated document components, their layout, their general properties and their relationships. Text, table and form are presentation components which are as exceptions directly integrated in HTML. All other presentation components such as images, movies, 3D worlds and interactive components are embedded by corresponding HTML tags with the specification of their source. Dynamic features of the document as well as navigation and printing support is realized by JavaScript. This functionality and the corresponding instruments are called 'Reporter'.

Engineering documents represent engineering information. This information is stored traditionally as separated data files and programs or in an object oriented way combined in objects. These objects can be integrated directly in Web based documents by Java applets. The access to this information is managed on the server side by servlets, so called 'Manager'. This manager enables the access to the used data or object bases, programs or other kind of information bases and the transmission of the information in Web supported representations. The applets and their associated multi-media components enable the presentation and editing of these engineering objects. Therefore they are called 'Editor'.

For each component semantic weighted keywords can be specified in meta information tags (e.g. XML http://www.w3c.org/XML). By these keywords and the linked project data objects (or a logical combination of them) it is possible to generate new semantic reading paths in addition to traditional text search dynamically. For example, the reader can generate a path in a coastal engineering report which includes information associated to a special tidal gauge, to a special numerical parameter or to a special time period. The order of the components in this path reflect a comprehensible sequence given by the weights on the keywords.

The described technological concept of Web based documents is just one concept. There are a lot of other possibilities depending on the application target domain. This concept integrates the traditional separated domain of documentation, presentation, visualization, analysis and model control in one environment. These innovative features have to be introduced in hydroengineering to overcome the lack of traditional paper based documents. One important pre-requisite for the successful introduction and application of Web based documents is the ability and willingness of humans to operate in this new environment - a challenge of training and education.

3.7.3 Authoring and Editing

Authoring and editing of Web based documents is different to traditional paper based documents. Each component has to be created and styled to represent information in a comprehensive way. Besides traditional text and two dimensional graphics a lot of new suitable and not suitable multi-media presentation types can be used. The decision which component type is most useful for which kind of information and the combination of different presentation types to a comprehensible component is much more complicated.

In traditional documents the components are structured in a sequence of pages. Web based documents use links between components to support a flexible non sequential structure. Components can be structured in a flexible way e.g. by pre-defined and dynamic reading paths or hierarchical (chapter oriented) trees. Author and reader can navigate through these structures. The definition of suggestions for reading paths and the specification for semantic meta information for dynamic reading paths is a new demanding task. Instruments and tools are not satisfactory up to now.

Interactive and dynamic features in Web based documents offer a new dimension of information exchange and knowledge repositories. The application of these features in Web based documents demands for the ability of the editor to operate with the corresponding software technologies in the Web environment. Several standard tasks can be supported by standard components based environments like StarOffice or Microsoft Office. Nevertheless, special features have to be implemented by the editor himself. This kind of 'programming' or 'implementation' is on a low level (direct implementing in JavaScript or Java) at the moment and might be supported in future by a higher level of software engineering tools. Independent of this evolution editing of interactive dynamic Web based documents demands for basic knowledge and experience in implementation techniques - a challenge for training and education.

3.7.4 Reading and Navigation

Reading and navigation in Web based documents is different to traditional paper documents. Paper based documents are page oriented and prepared for a sequential reading. Humans have learned to author, edit and finally read such kind of documents over centuries. Reading means the absorption and comprehension of the written information. This reading technique has to change for the non sequential structure of Web based documents from the sequential follow up of the pages towards navigation in the flexible net of linked information units. Reading in this network demands a higher level of concentration and content follow up by the reader and a support by semantic reading paths or other semantic structures for navigation. Navigation techniques are still a question of research and development.

The different components of Web based documents contain features for interactive, dynamic and multi-media information presentation. Traditional paper based documents only offer passive and static information presentation. The reader has to read them as they are - there is no possibility to change the presentation mode or to get direct access to the engineering information. Interactive and dynamic components change this situation dramatically. Depending on the provided features by the author the reader can change the presentation mode for his personal view and can use integrated functionality e.g. for data analysis. These new features demand the ability of the reader to interact with the Web based components and to understand the related mathematical and physical background.

The application of such Web based documents will not replace traditional documents but can complement documentation methods in all domains of the society. Of course it is not easy to change reading and writing techniques learned as child and handed down over generations. This is the reason, why real Web based documents till this day have not expound all of their benefits in the society. Only a few persons are prepared to write and read non sequential documents with an incomplete developed technology. Without doubt this will be overcome by time.

© FM April 2001

Preface | Part 1 | Part 2 | Part 3 | Part 4