Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Outline I. Web Applications I.1 History and Notions Web Engineering I.2 Categories of Web Applications I.3 Characteristics of Web Applications Winter Term 2006/07 I.4 Web Engineering Prof. Dr. Gregor Engels Chapter I: Web Applications Chapter 1 © Gregor Engels - University of Paderborn 4 Acknowledgements Motivation • Prof. Dr. Gerti Kappel, TU Wien • The World Wide Web is omnipresent! •Why? – global and permanent availability http://www.big.tuwien.ac.at/teaching/offer/ss05/we_vo/ – comfortable and uniform access – anyone can produce and publish contents • G. Kappel, B. Pröll, S. Reich, W. Retschitzegger (eds.): Web Engineering – The Discipline of Systematic Development of Web Applications. John Wiley & Sons 2006 Chapter 1 © Gregor Engels - University of Paderborn 2 Chapter 1 © Gregor Engels - University of Paderborn 5 Literature Example: Search Engine • G. Kappel, B. Pröll, S. Reich, W. Retschitzegger (Hrsg.): Web Engineering – Systematische Entwicklung von Web-Anwendungen. dpunkt.verlag 2004 • G. Alonso, F. Casati, H. Kuno, V. Machiraju: Web Services – Concepts, Architectures and Applications. Springer 2004 • H. Wöhr: Web-Technologien – Konzepte, Programmiermodelle, Architekturen. dpunkt.verlag 2004 • R. Pressman: Software Engineering – A Practitioner’s Approach, 6th Edition. McGraw-Hill Higher Education 2005 • A. Eberhart, St. Fischer: Java-Bausteine für E-Commerce-Anwendungen. Hanser 2001 • J. Conallen: Building Web Applications with UML. Addison-Wesley 1999 • M. P. Singh, M. N. Huhns: Service-Oriented Computing – Semantics, Processes, Agents. Wiley 2005 • to be continued … Chapter 1 © Gregor Engels - University of Paderborn 3 Chapter 1 © Gregor Engels - University of Paderborn 6 © Gregor Engels University of Paderborn 1 Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Example: Information Basic paradigms • Hypertext + Internet • Hypertext: textual documents together with the ability to interconnect documents by links between them as part of the document contents • HTML: HyperText Markup Language • http: HyperText Transfer Protocol Chapter 1 © Gregor Engels - University of Paderborn 7 Chapter 1 © Gregor Engels - University of Paderborn 10 Example: Course Announcement Conceptual Architecture Web-Browser Web-Server HTML HTML Web-Browser HTML Web-Browser HTML Client/Server Architecture Chapter 1 © Gregor Engels - University of Paderborn 8 Chapter 1 © Gregor Engels - University of Paderborn 11 Example: www.bahn.de History of the Web • 1969: ARPA (Advanced Research Projects Agency) – First small network: Stanford Research Institute, UCLA, UC Santa Barbara, Univ. of Utah – TCP (Transmission Control Protocol) – IP (Internet Protocol) • 1972: Telnet protocol • 1973: SMTP (Simple Mail Transfer Protocol) • 1973: FTP (File Transfer Protocol) • 1989: T. Berners-Lee et al.: Word Wide Web (WWW) • 1997: HTTP (HyperText Transfer Protocol) • 1994: W3C (World Wide Web Consortium) Chapter 1 © Gregor Engels - University of Paderborn 9 Chapter 1 © Gregor Engels - University of Paderborn 12 © Gregor Engels University of Paderborn 2 Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Protocol Stack Web Application client server Definition: A Web Application is a software system based on HTTP HTTP technologies and standards of the World Wide Web Consortium (W3C) that provides Web specific TCP TCP resources such as content and services through a IP IP user interface, the Web browser. physical layer Chapter 1 © Gregor Engels - University of Paderborn 13 Chapter 1 © Gregor Engels - University of Paderborn 16 World Wide Web Consortium (W3C) Outline • international consortium where member I. Web Applications organizations, a full-time staff, and the public work I.1 History and Notions together to develop Web standards I.2 Categories of Web Applications • http://www.w3.org I.3 Characteristics of Web Applications I.4 Web Engineering W3C's mission: • to lead the World Wide Web to its full potential by developing protocols and guidelines that ensure long-term growth for the Web. Chapter 1 © Gregor Engels - University of Paderborn 14 Chapter 1 © Gregor Engels - University of Paderborn 17 The W3C Technology Stack Categories of Web Applications complexity semantic web ubiquitious portal- oriented collaborative workflow- based transaction- oriented interactive document- centered http://www.w3.org/2004/10/RecsFigure.png historical development Chapter 1 © Gregor Engels - University of Paderborn 15 Chapter 1 © Gregor Engels - University of Paderborn 18 © Gregor Engels University of Paderborn 3 Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Categories of Web Applications (1) (cf. Pressman, p. 472, Kappel, p.7) Categories of Web Applications (4) • document-centered • workflow-based – Informational – support business processes („workflows“) within resp. read-only content is provided with simple navigation and links between different enterprises or private users – Download – an application provides a complex service to the user, e.g. a user downloads information from the appropriate server (ftp-server) assists the user in determing the mortgage payment – Customizable – prerequisite: structured flow of activities the user customizes content to specific needs – examples: • static HTML-pages, „home pages“ – examples: • web radio • Business-to-Business (B2B) Integration Frameworks • simple presentations of companies/products • E-Government • patient workflows in health care systems Chapter 1 © Gregor Engels - University of Paderborn 19 Chapter 1 © Gregor Engels - University of Paderborn 22 Categories of Web Applications (2) Categories of Web Applications complexity • interactive semantic web – content of a website is dynamically generated as response to a user request ubiquitious – form-based input is the primary mechanism for communication between client and server portal- – usage of HTML-forms and Common Gateway Interface (CGI) oriented techniques collaborative • radio button, string input, choice lists workflow- Browser Web-Server based HTML transaction- – examples: oriented • dynamic HTML pages interactive • public transport schedules • search engines CGI document- program centered historical development Chapter 1 © Gregor Engels - University of Paderborn 20 Chapter 1 © Gregor Engels - University of Paderborn 23 Categories of Web Applications (3) Categories of Web Applications (5) • transaction-oriented • Collaborative – complex interactions – support cooperation in case of unstructured flow of activities and high degree of communication – read and write actions – „groupware“ – usage of transaction management of database systems • efficient and consistent data management • structured data and queries – examples: • support of shared information- and workspaces – examples: – Wiki, http://c2.com/cgi/wiki • online banking – BSCW, http://bscw.gmd.de • e-shopping – chatrooms • e-Learning platforms • reservation systems Chapter 1 © Gregor Engels - University of Paderborn 21 Chapter 1 © Gregor Engels - University of Paderborn 24 © Gregor Engels University of Paderborn 4 Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Categories of Web Applications (6) Categories of Web Applications complexity semantic • portal-oriented web – the application channels the user to other Web content or ubiquitious services outside the domain of the portal application portal- – „single point of access“ oriented collaborative – examples: workflow- based • Community portals transaction- – dedicated user groups oriented – customer profiles interactive • enterprise portals – Intranet, extranet document- centered historical development Chapter 1 © Gregor Engels - University of Paderborn 25 Chapter 1 © Gregor Engels - University of Paderborn 28 Categories of Web Applications (7) Outline • ubiquitious I. Web Applications – personalized services at every time at every location I.1 History and Notions – multi-platform delivery (PC, PDA, mobile phone) I.2 Categories of Web Applications – context-dependent information I.3 Characteristics of Web Applications I.4 Web Engineering – example: • display of today‘s menu on end-user devices while entering a restaurant Chapter 1 © Gregor Engels - University of Paderborn 26 Chapter 1 © Gregor Engels - University of Paderborn 29 Categories of Web Applications (8) Navigation in Web Applications (1) • semantic web – information available on the web • adequate for human understanding and • adequate for automatic manipulation – „knowledge management“ • derivation of new knowledge • re-use of knowledge • based on ontologies –Example: • Web 2.0 • social software: wiki, Flickr, del.icio.us • Google Chapter 1 © Gregor Engels - University of Paderborn 27 Chapter 1 © Gregor Engels - University of Paderborn 30 © Gregor Engels University of Paderborn 5 Web Engineering WT 2005/06 2005-10-18 Chapter 1:Web Applications Development of Web Applications: Error! Link not found! today’s approach • ad-hoc development • based on knowledge, experiences and practices of individual developers • reuse of existing applications by “copy&paste” approach • insufficient documentation of design decisions • isolated activity: no “design for change” • missing methodical approach Chapter 1 © Gregor Engels - University of Paderborn 31 Chapter 1 © Gregor Engels - University of Paderborn 34 Navigation in Web Applications (2) Reasons for Quality Deficiencies • document-centered view – development of web applications seen as editorial activity: “ (textual) web pages, links