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Carnegie Mellon Univ. Dept. of Computer Science 15-415/615 - DB Applications

Carnegie Mellon Univ. Dept. of Computer Science 15-415/615 - DB Applications. C. Faloutsos - A. Pavlo Lecture#2: E-R diagrams. Administrivia. Course url: http://15415.courses.cs.cmu.edu/ Course policies http://15415.courses.cs.cmu.edu/fall2016/policies.html Foils in pps:

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Carnegie Mellon Univ. Dept. of Computer Science 15-415/615 - DB Applications

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  1. Carnegie Mellon Univ.Dept. of Computer Science15-415/615 - DB Applications C. Faloutsos - A. Pavlo Lecture#2: E-R diagrams

  2. Administrivia • Course url: • http://15415.courses.cs.cmu.edu/ • Course policies • http://15415.courses.cs.cmu.edu/fall2016/policies.html • Foils in pps: • http://15415.courses.cs.cmu.edu/fall2016/slides-pps/ CMU SCS 15-415/615

  3. Course Topics ✔ • Introduction to DBMSs • Data Models • Query Language (SQL) • Database Design • Query Optimization & Indexing • Transaction Management • Advanced Topics CMU SCS 15-415/615

  4. Problem • Develop an application for U.G. admin: • Student info • Who-takes-what class • Class rosters • Transcripts • How do you proceed? • (Which role(s) are you playing?) CMU SCS 15-415/615

  5. Database users • ‘naive’ users • casual users • application programmers • [ DBA (Data base administrator)] CMU SCS 15-415/615

  6. Casual users select * from student DBMS and meta-data = catalog data CMU SCS 15-415/615

  7. ``Naive’’ users Pictorially: app. (eg., report generator) DBMS and meta-data = catalog data CMU SCS 15-415/615

  8. App. programmers • Authors of applications (like the ‘report generator’) app. (eg., report generator) DBMS and meta-data = catalog data CMU SCS 15-415/615

  9. DB Administrator (DBA) • Duties? DBMS and meta-data = catalog data CMU SCS 15-415/615

  10. DB Administrator (DBA) • Duties? DBMS and meta-data = catalog data CMU SCS 15-415/615

  11. DB Administrator (DBA) • schema definition (‘logical’ level) • physical schema (storage structure, access methods • schema modifications • granting authorizations • integrity constraint specification CMU SCS 15-415/615

  12. Problem • Develop an application for U.G. admin: • Student info • Who-takes-what class • Class rosters • Transcripts • How do you proceed? • (Which role(s) are you playing?) CMU SCS 15-415/615

  13. Database users • ‘naive’ users • casual users • application programmers • [ DBA (Data base administrator)] CMU SCS 15-415/615

  14. Database Design • Requirements Analysis • Conceptual Design • Logical Design • Schema Refinement • Physical Design • Security Design CMU SCS 15-415/615

  15. Database Design ✔ user’s needs high level (ER) Tables Normalization Indices etc Access controls • Requirements Analysis • Conceptual Design • Logical Design • Schema Refinement • Physical Design • Security Design CMU SCS 15-415/615

  16. Problem’ Maintain • Develop an application for U.G. admin: • Student info • Who-takes-what class • Class rosters • Transcripts • If you are the *new* DBA, what would you rather inherit: CMU SCS 15-415/615

  17. This or this ? drop table if exists student; create table student (ssn fixed, name char(20)); drop table if exists takes; create table takes (ssn fixed, cid char(10), grade fixed); Student Takes Course CMU SCS 15-415/615

  18. True story • Health insurance company • Wants to catch (some of the abundant) fraud • Schema: • patients, visit doctors, get medicine, • Doctors perform operations, … • Nurses monitor patients, … • etc etc • Q: How many tables do you think it spans? CMU SCS 15-415/615

  19. True story • Schema: • patients, visit doctors, get medicine, • Doctors perform operations, … • Nurses monitor patients, … • etc etc • Q: How many tables do you think it spans? 10? 20? 30? CMU SCS 15-415/615

  20. True story • Schema: • patients, visit doctors, get medicine, • Doctors perform operations, … • Nurses monitor patients, … • etc etc • Q: How many tables do you think it spans? 10? 20? 30? • A: 120 PAGES of schema CMU SCS 15-415/615

  21. Motivation & upcoming conclusion: • E-R diagrams are excellent documentation tools Student Takes • drop table if exists student; • create table student • (ssn fixed, • name char(20)); • drop table if exists takes; • create table takes • (ssn fixed, • cid char(10), • grade fixed); Course CMU SCS 15-415/615

  22. Overview • concepts • Entities • Relationships • Attributes • Specialization/Generalization • Aggregation • ER modeling questions Basic Advanced/ rare CMU SCS 15-415/615

  23. Tools Entities (‘entity sets’) Student Relationships (‘rel. sets’) and mapping constraints N M Takes P attributes Course CMU SCS 15-415/615

  24. Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets CMU SCS 15-415/615

  25. Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets CMU SCS 15-415/615

  26. Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets CMU SCS 15-415/615

  27. ... name STUDENT ssn INSTRUCTOR primary key = unique identifier -> underline issn CMU SCS 15-415/615

  28. ... name STUDENT c-id ssn c-name COURSE INSTRUCTOR issn but: sections of course (with different instructors)? CMU SCS 15-415/615

  29. ssn STUDENT c-id COURSE SECTION s-id but: s-id is not unique... (see later) INSTRUCTOR issn CMU SCS 15-415/615

  30. ssn STUDENT c-id COURSE SECTION s-id Q: how to record that students take courses? INSTRUCTOR issn CMU SCS 15-415/615

  31. ssn STUDENT N c-id takes M COURSE s-id SECTION INSTRUCTOR issn CMU SCS 15-415/615

  32. STUDENT N c-id takes M s-id SECTION COURSE N teaches 1 INSTRUCTOR CMU SCS 15-415/615

  33. STUDENT N c-id takes M 1 N has s-id SECTION COURSE N teaches 1 INSTRUCTOR CMU SCS 15-415/615

  34. Cardinalities 1 1 • 1 to 1 (example?) • 1 to N • N to M 1 N N M CMU SCS 15-415/615

  35. Cardinalities 1 1 has CAPITAL COUNTRY 1 N owns PERSON CAR N M takes SECTION STUDENT CMU SCS 15-415/615

  36. Cardinalities has CAPITAL COUNTRY Book’s notation: owns PERSON CAR takes SECTION STUDENT CMU SCS 15-415/615

  37. Cardinalities 1 1 has CAPITAL COUNTRY Book’s notation vs 1 to N notation 1 N owns PERSON CAR N M takes SECTION STUDENT CMU SCS 15-415/615

  38. Cardinalities 1 1 has CAPITAL COUNTRY 1 N owns PERSON CAR N M takes SECTION STUDENT CMU SCS 15-415/615

  39. ‘Total/partial’ participation 1:1 1:1 total, total has CAPITAL COUNTRY ?:1 ?:N owns PERSON CAR ?? ?:N ?:M takes SECTION ?? STUDENT CMU SCS 15-415/615

  40. ‘Total/partial’ participation 1:1 1:1 total, total has CAPITAL COUNTRY 1:1 0:N owns PERSON CAR partial, total ?:N ?:M takes SECTION ?? STUDENT CMU SCS 15-415/615

  41. ‘Total/partial’ participation 1:1 1:1 total, total has CAPITAL COUNTRY 1:1 0:N owns PERSON CAR partial, total 1:N 0:M takes SECTION partial, total STUDENT CMU SCS 15-415/615

  42. ‘Total/partial’ participation Is it ‘legal’? partial, total 1:1 0:N owns PERSON CAR CMU SCS 15-415/615

  43. ‘Total/partial’ participation Is it ‘legal’? partial, total NO! why not? 1:1 0:N owns PERSON CAR CMU SCS 15-415/615

  44. Subtle concept: Weak entities • ‘section’ has no unique-id of its own!(?) c-id 1 N s-id has COURSE SECTION CMU SCS 15-415/615

  45. Weak entities • ‘weak’ entities: if they need to borrow a unique id from a ‘strong entity - thick box. • ‘c-id’ + ‘s-id’: unique id for SECTION • partial key (eg., ‘s-id’) - dashed-underline • identifying relationship (eg., ‘has’) c-id 1 N s-id has SECTION COURSE CMU SCS 15-415/615

  46. Weak entities • Other example(s) of weak entities? ??id 1 N ?? ?? ??? ??? CMU SCS 15-415/615

  47. Weak entities • Other example(s) of weak entities? e-id 1 N name has Dependent Employee CMU SCS 15-415/615

  48. More details • self-relationships - example? ?? ?? ?? ?? CMU SCS 15-415/615

  49. More details • self-relationships - example? manages 1 EMPLOYEE N CMU SCS 15-415/615

  50. More details • self-relationships - example? Has-friend ?? FB user ?? CMU SCS 15-415/615

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