CSC340Information Systems Analysis and DesignWeb Design -- 1© 2001 Paolo AtzeniXXII. Website DesignThe WebHypertext Data IndependenceData Models for Hypertext DocumentsThe Araneus Data Model (ADM)The Navigational Conceptual Model (NCM)The Araneus Methodology for Website DesignCSC340Information Systems Analysis and DesignWeb Design -- 2© 2001 Paolo AtzeniThe Web The spread of World-Wide Web (hereafter “Web”) technology isone of the most remarkable phenomena of the last few years inall areas of computing and communication. The Web (e.g., Web browsers) is becoming a standard interfacefor the general public to access and exchange information: The protocol is very simple and public; The interface is uniform; The content is extremely rich (both in breadth and in depth); Moreover, the Web is becoming a standard interface foraccessing many specialized services, specifically informationsystems and databases of every type.CSC340Information Systems Analysis and DesignWeb Design -- 3© 2001 Paolo AtzeniWeb Features and Open Problems The Web is a simple and powerful data integration tool. Two basic approaches to Web-based data integration: Coarse-grain: pages of hypertext; Fine-grain: unified interface for accessing different (usuallysimilar) information systems available on the Web. The Web is built out of semi-structured (HTML/XML) documents,databases contain structured (I.e., tuple/record) data. Databases can be queried in a flexible way; hypertextdocuments are easy to access, but cannot be “queried”. Web sites are often difficult to explore, use and monitor. Web sites are also difficult to design and maintain.CSC340Information Systems Analysis and DesignWeb Design -- 4© 2001 Paolo AtzeniProblems with Large Websites Information is often poorly organized and difficult to access. It is often unclear what information is available on a givenwebsite. The access structure of many websites is casual andidiosyncratic, causing frequent dangling references. The style of presentation is often heterogeneous. Large websites are usually difficult to update, or change theirstructure. It is also difficult to change the presentation structure and/ordetails.CSC340Information Systems Analysis and DesignWeb Design -- 5© 2001 Paolo AtzeniData Independence for HypertextDocuments You might say that there are three facets to the Web:Data -- what information is offered through the site and whatare the conceptual details and the logical organization;Hypertext -- how data is arranged in pages and whatnavigation links correlate them;Presentation -- the appearance of each piece of informationon each pages. As much as possible, we’d like to decouple the three, so thatchanges to one affect minimally the other two facets of the Web.CSC340Information Systems Analysis and DesignWeb Design -- 6© 2001 Paolo AtzeniAn ExampleCSC340Information Systems Analysis and DesignWeb Design -- 7© 2001 Paolo Atzeni...Another...CSC340Information Systems Analysis and DesignWeb Design -- 8© 2001 Paolo Atzeni…and Another...CSC340Information Systems Analysis and DesignWeb Design -- 9© 2001 Paolo AtzeniDesign Issues Data -- choose the content Hypertext -- choose navigation paths Presentation -- define layout and graphicsData -- changing the contentHypertext -- changing navigation pathsPresentation -- changing layout and graphicsMaintenance IssuesDataER and RelationalHypertextPresentationHTMLComponents and ModelsWhat ismissing is amodel forhypertexts!CSC340Information Systems Analysis and DesignWeb Design -- 10© 2001 Paolo AtzeniModels for Hypertext Documents In data-intensive Websites (and often in general) there are(many) pages with a similar (or even the same) structure. Forty years ago people realized that in an application it is oftenthe case that there are many records with the same structure;files and file technology were invented to exploit this fact. Likewise, the notion of a schema for a database was laterintroduced as an overall description of the content of a database. We need something similar for the Web!CSC340Information Systems Analysis and DesignWeb Design -- 11© 2001 Paolo AtzeniA Web PageCSC340Information Systems Analysis and DesignWeb Design -- 12© 2001 Paolo AtzeniA Page Schema: ProfessorPageProfessorPageNamePositionAddressEMailResearchListAreaToResPText elementsList elementCSC340Information Systems Analysis and DesignWeb Design -- 13© 2001 Paolo AtzeniADM (Araneus Data Model):A Logical Model for HypertextDocuments Developed at the University of Rome III (Universita di RomaTre) by Paolo Atzeni, Paolo Merialdo, Giansalvatore Mecca andcolleagues. Its features include: Page schemas Simple attributes text, images, ... link (anchor, URL) Complex attributes such as lists, possibly nested. A heterogeneous union operation. Forms as virtual lists over form fields and links to a result.CSC340Information Systems Analysis and DesignWeb Design -- 14© 2001 Paolo AtzeniAnother Web Page-- Containing a List of LinksCSC340Information Systems Analysis and DesignWeb Design -- 15© 2001 Paolo AtzeniA Page Schema forProfessorListPageProfessorListPageProfessorListNameToProfPCSC340Information Systems Analysis and DesignWeb Design -- 16© 2001 Paolo AtzeniAn ADM SchemaProfessorListPageProfessorListNameToProfPProfessorPageNamePositionAddressEMailResearchListAreaToResPCSC340Information Systems Analysis and DesignWeb Design -- 17© 2001 Paolo AtzeniHeterogeneous Union and FormsCSC340Information Systems Analysis and DesignWeb Design -- 18© 2001 Paolo AtzeniHeterogeneous Union and FormsProfessorListPageProfessorListNameToProfPProfessorPageNamePositionAddressEMailResearchListAreaToResPNameSubmitUSearchProfPageForm elementCSC340Information Systems Analysis and DesignWeb Design -- 19© 2001 Paolo AtzeniData Models, AgainERADMDatabase ConceptualSchema(entities - relationships)Hypertext LogicalSchema(page schemas, links)There is considerable conceptual distancebetween the two!CSC340Information Systems Analysis and DesignWeb Design -- 20© 2001 Paolo AtzeniA Simple ER SchemaCSC340Information Systems Analysis and DesignWeb Design -- 21© 2001 Paolo AtzeniAn ADM SchemaCSC340Information Systems Analysis and DesignWeb Design -- 22© 2001 Paolo AtzeniHypertext LogicalSchema(page schemas, links)ERNCMHypertext ConceptualSchema(macroentities,directed
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