WEB SITES NEED MODELS AND SCHEMES

Transcription

1 WEB SITES NEED MODELS AND SCHEMES Paolo Atzeni Dipartimento di informatica e automazione Università di Roma Tre

2 Outline Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 2

3 Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 3

4 Database and information systems technology: present and future the technology of relational databases is now mature and reliable: a de-facto standard for business applications the current challenge is integration: integration of technologies integration of distributed, autonomous, heterogeneous systems Paolo Atzeni ER98 4

5 The need for cross-fertilization database technology was developed within the domain of business applications; other domains have other requirements (also very different from each other) database technology and X technology can be complementary, with potential mutual benefit basic problems have been solved; specific areas may have specific problems, for which the general solutions need not be satisfactory Paolo Atzeni ER98 5

6 Integration of information systems Various motivations: interaction of components independently developed cooperation of previously separated business processes cooperation (or merge) of companies Typical requirements: distribution heterogeneity autonomy Paolo Atzeni ER98 6

7 A topical issue a request from our users : computing facilities should become similar to standard utilities (gas, phone, power, etc.) our usual reply: computing services have application specific features for which standard services would only be a limited solutions (as it is the case for the other utilities) however what would a standard offer of services be? Paolo Atzeni ER98 7

8 The great opportunity Internet (and Intranets and Extranets) and the World-Wide-Web offer a great opportunity a simplified stack of layers: cooperation (of applications) interoperability (ftp, telnet, mail, http,...) connectivity standardization climbs stacks (functionalities get standardized and go down: think to database systems!) Paolo Atzeni ER98 8

9 The Web: a great opportunity the diffusion of the Web is... the Web (with its browsers) is becoming a standard interface for the final user the protocol is very simple and public the interface is uniform the content is very rich (in breadth and depth) it is becoming a standard interface for accessing many services, with information systems and databases of every type Paolo Atzeni ER98 9

10 Evolution of the Web Publishing information Interactive services Cooperative work Integration (of sources, services, etc.) Embedded systems Extranets Paolo Atzeni ER98 10

11 Web and DBs: a contradiction? databases are well structured and organized how much structure and organization is there in the Web? it depends, both on the source and on the user there are different degrees of granularity and structure for our data we need to be able to make conversions (from DB to HT and viceversa) Paolo Atzeni ER98 11

12 we need the best of databases and hypertexts! Paolo Atzeni ER98 12

13 Database perspectives on the Web What is the equivalent of a database (a source of data )? a page independently of the others the whole Web a site Paolo Atzeni ER98 13

14 Database approaches bottom-up: accessing information from Web sources top-down: designing and maintaining Web sites global: integrating existing sites and offering the information through new ones Paolo Atzeni ER98 14

15 Integration on the Web the Web is a simple and powerful integration tool; it allows the natural implementation of (data-centred) cooperative approach various approaches: coarse integration: pages of hypertextual links fine-grain integration: unified interfaces for accessing different (usually similar) information systems available on the Web Paolo Atzeni ER98 15

16 Problems Databases can be queried in a flexible way; hypertexts are easy to access, but cannot be queried Web sites are often difficult to explore, use and monitor Web sites are difficult to design and maintain Paolo Atzeni ER98 16

17 Database approaches bottom-up: accessing information from Web sources, and integrating them top-down: designing and maintaining Web sites global: integrating existing sites and offering the information through new ones Paolo Atzeni ER98 17

18 Web-based information systems: a database point of view Data-Intensive Web Sites: large amount of data significance the hypertext structure Paolo Atzeni ER98 18

19 Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 19

20 Problems with many Web-sites (design) information is often poorly organized and difficult to access it is not even clear which pieces of information are available the access structure is casual and many dandling references occur the style of presentation is heterogeneous Paolo Atzeni ER98 20

21 Problems with many Web-sites (maintenance) difficulties in updating the content difficulties in changing the initially defined structure difficulties in changing the presentation details Paolo Atzeni ER98 21

22 Web-based information systems What we have: DBMSs for the management of data various tools for the generation of Web pages What we advocate: a systematic approach to Web site design: models, steps, guidelines tools to support the development process Paolo Atzeni ER98 22

23 Hypertext data-independence Paolo Atzeni ER98 23

24 Hypertext data-independence Paolo Atzeni ER98 24

25 Hypertext data-independence Paolo Atzeni ER98 25

26 Hypertext data-independence Data what information is offered through the site and what are the conceptual details and the logical organization Hypertext how data is arranged in pages and what navigation links correlate them Presentation the appearance of each piece of information in pages Paolo Atzeni ER98 26

27 Design Issues Data choosing the content Hypertext choosing navigation paths Presentation defining layout and graphics Paolo Atzeni ER98 27

28 Maintenance Issues Data changing the content Hypertext changing navigation paths Presentation changing layout and graphics Paolo Atzeni ER98 28

29 Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 29

30 Components and Models data hypertext presentation ER and Relational HTML What is missing is a model for hypertexts! Paolo Atzeni ER98 30

31 Models for hypertexts in data-intensive Web sites (and often in general) there are (many) pages with a similar (or even the same) structure thirty or forty years ago people realized that in an application it is often the case that there are records with the same structure; files with a rather fixed structure were invented with this purpose the notion of scheme of the database was later introduced as an overall description of the content of a database Paolo Atzeni ER98 31

32 A Web page Paolo Atzeni ER98 32

33 A page-scheme: ProfessorPage ProfessorPage Name Position Address ResearchList Area ToResP Paolo Atzeni ER98 33

34 ADM (Araneus Data Model): a logical model for Web hypertexts page-schemes unique pages simple attributes text, images,... link (anchor, URL) complex attributes: lists (possibly nested) heterogeneous union form (as virtual list over form fields and link to the result) Paolo Atzeni ER98 34

35 A Web page (containing a list of links) Paolo Atzeni ER98 35

36 A unique page-scheme: ProfessorListPage ProfessorListPage ProfessorList Name ToProfP Paolo Atzeni ER98 36

37 An ADM Scheme ProfessorListPage ProfessorList Name ToProfP ProfessorPage Name Position Address ResearchList Area ToResP Paolo Atzeni ER98 37

38 Heterogeneous Union and Forms Paolo Atzeni ER98 38

39 Heterogeneous Union and Forms in ADM SearchProfPage Name Submit ProfessorListPage ProfessorList Name ToProfP U ProfessorPage Name Position Address ResearchList Area ToResP Paolo Atzeni ER98 39

40 Data Models ER Database Conceptual Scheme (entities - relationships) ADM Hypertext Logical Scheme (page-schemes, links) There is a lot of distance between the two! Paolo Atzeni ER98 40

41 A simple ER scheme Paolo Atzeni ER98 41

42 An ADM scheme Paolo Atzeni ER98 42

43 NCM Hypertext Conceptual Scheme (macroentities, directed relationships, aggregations) Paolo Atzeni ER98 43

44 Data Models ER NCM ADM Database Conceptual Scheme (entities - relationships) Hypertext Conceptual Scheme (macroentities, directed relationships, aggregations) Hypertext Logical Scheme (page-schemes, links) NCM fills the gap between the two Paolo Atzeni ER98 44

45 Navigation Conceptual Model (NCM) Hypertext Conceptual Features Which concepts should be the hypertext nodes Which should be the navigation paths between nodes How nodes should be aggregated to build the hierarchical access structure NCM Constructs Macroentity Directed Relationship Aggregation Paolo Atzeni ER98 45

46 NCM: Macroentities and directed relationships Name Room Professor 1:N 1:1 Tutorship Student Name... Teacher Name Description 1:1 Course N Lesson Day Room Hour Paolo Atzeni ER98 46

47 NCM: aggregation nodes Department People Activities Student Professor Course Seminar 1:1 Tutorship 1:N Teacher 1:1 Paolo Atzeni ER98 47

48 An NCM scheme Paolo Atzeni ER98 48

49 Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 49

50 The Araneus Methodology Requirements analysis Database conceptual design Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 50

51 design from scratch Requirements analysis Database conceptual design Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 51

52 design from an existing database (with an ER scheme) Requirements analysis Database conceptual design Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 52

53 design from an existing database (without an ER scheme) Requirements analysis Database conceptual design (reverse engineering) Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 53

54 Hypertext conceptual design: from ER to NCM Requirements analysis Database conceptual design Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 54

55 Hypertext Conceptual Design ER scheme NCM Scheme step 1 choose and describe macroentities: design views over the input ER scheme step 2 choose navigation paths step 3 shape the hypertext access structure on the basis of ( bottom-up ) conceptual aggregation Paolo Atzeni ER98 55

56 Hypertext Conceptual Design ER scheme NCM Scheme step 1 choose and describe macroentities: design views over the input ER scheme usually it corresponds to de-normalize the input ER scheme ER NCM Course 1:N 1:1 Lesson Name Description Day Hour Course 1:N Lesson Name Description Day Hour Paolo Atzeni ER98 56

57 Hypertext Conceptual Design ER scheme NCM Scheme step 2 choose navigation paths it may introduce redundancies ER NCM 1:N 1:N Paper Professor 1:1 1:N Research-Group 1:N 1:N Paper 1:N 1:N Professor 1:1 1:N Research-Group Paolo Atzeni ER98 57

58 Hypertext Conceptual Design ER scheme NCM Scheme step 3 shape the hypertext access structure it is based on bottom-up conceptual aggregations... NCM Professor Research Activities NCM Professor Seminar 1:1 1:N Research-Group Seminar... 1:1 1:N Research-Group Paolo Atzeni ER98 58

59 The Input ER scheme Paolo Atzeni ER98 59

60 The resulting NCM scheme Paolo Atzeni ER98 60

61 Hypertext logical design: from NCM to ADM Requirements analysis Database conceptual design Hypertext conceptual design Database logical design Hypertext logical design Presentation design Site Page generation Generation Paolo Atzeni ER98 61

62 Hypertext Logical Design NCM scheme ADM Scheme step 1 map each macroentity into either a page-scheme or a list inside a page-scheme step 2 map each directed relationship into a (list of) link attribute(s) step 3 map each aggregation into a unique pagescheme with link attributes to the target page-schemes Paolo Atzeni ER98 62

63 Hypertext Logical Design Step 1 (example) Paolo Atzeni ER98 63

64 Hypertext Logical Design Step 1 (example) Paolo Atzeni ER98 64

65 Hypertext Logical Design Step 2 (example) Paolo Atzeni ER98 65

66 Hypertext Logical Design Step 3 (example) Paolo Atzeni ER98 66

67 R es u lt i ng A DM S ch e me Paolo Atzeni ER98 67

68 Maintenance The Schemes help designers to maintain the hypertext structure Maintenance activities correspond to apply scheme transformations: introduce multilevel lists introduce forms split pages... Paolo Atzeni ER98 68

69 Maintenance: example Paolo Atzeni ER98 69

70 Databases and information systems over the Web: a great opportunity The design of Web-based information systems (WBIS) Models for the design of WBIS Conceptual and logical design of WBIS Conclusions Paolo Atzeni ER98 70

71 Conclusions Models and schemes are essential in the design and documentation of Web sites can help in the generation of Web sites can also be useful to support querying, extraction, and integration Paolo Atzeni ER98 71

72 DBLP Site at Trier Paolo Atzeni ER98 72

73 DBLP Site at Trier: ADM Scheme Paolo Atzeni ER98 73

74 Queries over Web Sites: Wrappers The need of Wrappers; E.F. Codd Internet wrapper Name : TEXT HTML ADM Pages are often logically homogeneous but physically heterogeneous; Paolo Atzeni ER98 74

75 Queries over Web Sites: Reverse Engineering Building a database representation of a site is a reverse engineering process; First Step: Deriving the logical structure of data in the site; Second Step: Wrapping pages in order to map physical HTML sources to database objects; Both processes should be automated; Paolo Atzeni ER98 75

76 Queries over Web Sites: Query Interfaces: Ulixes Example of SQL Query: "All papers by Codd in the VLDB Conference" DEFINE TABLE VLDBPapersByCodd(Title, Year) AS AuthorSearchPage.NameForm.Submit -> AuthorPage.WorkList IN DBLPScheme USING AuthorPage.WorkList.Title, AuthorPage.WorkList.Year, WHERE AuthorSearchPage.NameForm.Name='E. F. Codd AND AuthorPage.WorkList.Reference LIKE '%VLDB%' Paolo Atzeni ER98 76

77 Integration of Web Sites Data-Centered Cooperative Applications on the Web: Extraction of data from existing sites; Correlation; Generation of new sites; Dealing with Heterogeneities: Schematic heterogeneities; Semantic heterogeneities; Paolo Atzeni ER98 77

78 Integration of Web Sites in Araneus Paolo Atzeni ER98 78

79 Integration of Web Sites: The Integrated Web Museum Integrates data coming from several Virtual Museums from the Web (Uffizi, Louvre and Capodimonte); Data are re-organized: Uffizi, paintings organized by rooms; Louvre, Capodimonte, works organized by collections; Integrated Museum, data organized by author. Paolo Atzeni ER98 79

80 The Integrated Web Museum Paolo Atzeni ER98 80

81 The Integrated Web Museum Paolo Atzeni ER98 81

82 Bibliography Will be available soon (together with the presentation) on my Web site: Paolo Atzeni ER98 82

83 Acknowledgements The Araneus project at Roma Tre: Gianni Mecca Paolo Merialdo Alessandro Masci Valter Crescenzi Giuseppe Sindoni Marco Magnante Paolo Atzeni ER98 83