Carnegie Mellon Univ. Dept. of Computer Science /615 - DB Applications. Problem. Faloutsos - Pavlo CMU SCS /615

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1 Faloutsos - Pavlo /615 Carnegie ellon Univ. Dept. of Computer Science /615 - DB Applications C. Faloutsos - A. Pavlo Lecture#2: E-R diagrams 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?) Faloutsos - Pavlo /615 2 Database Design Requirements Analysis Conceptual Design Logical Design Schema Refinement Physical Design Security Design Faloutsos - Pavlo /

2 Faloutsos - Pavlo /615 Database Design Requirements Analysis Conceptual Design Logical Design Schema Refinement Physical Design Security Design user s needs high level (ER) Tables ormalization Indices etc Access controls Faloutsos - Pavlo /615 4 aintain Problem 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: Faloutsos - Pavlo /615 5 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 Faloutsos - Pavlo /

3 Faloutsos - Pavlo /615 True story Health insurance company Wants to catch (some of the abundant) fraud Schema: patients, visit doctors, get medicine, Doctors perform operations, urses monitor patients, etc etc Q: How many tables do you think it spans? Faloutsos - Pavlo /615 7 True story Schema: patients, visit doctors, get medicine, Doctors perform operations, urses monitor patients, etc etc Q: How many tables do you think it spans? 10? 20? 30? Faloutsos - Pavlo /615 8 True story Schema: patients, visit doctors, get medicine, Doctors perform operations, urses monitor patients, etc etc Q: How many tables do you think it spans? 10? 20? 30? A: 120 PAGES of schema Faloutsos - Pavlo /

4 Faloutsos - Pavlo /615 otivation & upcoming conclusion: E-R diagrams are excellent documentation tools Student Takes Course Faloutsos - Pavlo / concepts Entities Overview Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo / Tools Entities ( entity sets ) Student Takes Course Relationships ( rel. sets ) P and mapping constraints attributes Faloutsos - Pavlo /

5 Faloutsos - Pavlo /615 Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets Faloutsos - Pavlo / Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets Faloutsos - Pavlo / Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets Faloutsos - Pavlo /

6 Faloutsos - Pavlo /615 name... STUDET ssn ISTRUCTOR issn primary key = unique identifier -> underline Faloutsos - Pavlo / name ssn STUDET c-id c-name COURSE issn ISTRUCTOR but: sections of course (with different instructors)? Faloutsos - Pavlo / ssn STUDET c-id s-id SECTIO COURSE issn ISTRUCTOR but: s-id is not unique... (see later) Faloutsos - Pavlo /

7 Faloutsos - Pavlo /615 ssn STUDET c-id s-id SECTIO COURSE issn ISTRUCTOR Q: how to record that students take courses? Faloutsos - Pavlo / ssn s-id STUDET takes SECTIO c-id COURSE issn ISTRUCTOR Faloutsos - Pavlo / STUDET takes s-id SECTIO teaches 1 ISTRUCTOR c-id COURSE Faloutsos - Pavlo /

8 Faloutsos - Pavlo /615 STUDET takes s-id SECTIO teaches 1 ISTRUCTOR 1 has c-id COURSE Faloutsos - Pavlo / to 1 (example?) 1 to to Cardinalities Faloutsos - Pavlo / Cardinalities 1 1 COUTRY has CAPITAL PERSO 1 owns CAR STUDET takes SECTIO Faloutsos - Pavlo /

9 Faloutsos - Pavlo /615 Cardinalities COUTRY has CAPITAL Book s notation: PERSO owns CAR STUDET takes SECTIO Faloutsos - Pavlo / Book s notation vs 1 to notation Cardinalities 1 1 COUTRY has 1 PERSO owns CAPITAL CAR STUDET takes SECTIO Faloutsos - Pavlo / Cardinalities 1 1 COUTRY has CAPITAL PERSO 1 owns CAR STUDET takes SECTIO Faloutsos - Pavlo /

10 Faloutsos - Pavlo /615 Total/partial participation 1:1 1:1 total, total COUTRY has CAPITAL?? PERSO?:1?: owns CAR?? STUDET?: takes?: SECTIO Faloutsos - Pavlo / Total/partial participation 1:1 1:1 total, total COUTRY has CAPITAL partial, total PERSO 1:1 0: owns CAR?? STUDET?: takes?: SECTIO Faloutsos - Pavlo / Total/partial participation 1:1 1:1 total, total COUTRY has CAPITAL partial, total PERSO 1:1 0: owns CAR partial, total STUDET 1: 0: takes SECTIO Faloutsos - Pavlo /

11 Faloutsos - Pavlo /615 Total/partial participation Is it legal? partial, total PERSO 1:1 0: owns CAR Faloutsos - Pavlo / Total/partial participation Is it legal? O! why not? partial, total PERSO 1:1 0: owns CAR Faloutsos - Pavlo / Subtle concept: Weak entities section has no unique-id of its own!(?) c-id s-id SECTIO 1 has COURSE Faloutsos - Pavlo /

12 Faloutsos - Pavlo /615 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 SECTIO partial key (eg., s-id ) - dashed-underline identifying relationship (eg., has ) c-id s-id SECTIO 1 has COURSE Faloutsos - Pavlo / Weak entities Other example(s) of weak entities???id 1?????????? Faloutsos - Pavlo / Weak entities Other example(s) of weak entities? e-id name Dependent 1 has Employee Faloutsos - Pavlo /

13 Faloutsos - Pavlo /615 ore details self-relationships - example????????? Faloutsos - Pavlo / ore details self-relationships - example? 1 manages EPLOYEE Faloutsos - Pavlo / ore details self-relationships - example??? Has-friend FB user?? Faloutsos - Pavlo /

14 Faloutsos - Pavlo /615 ore details 3-way and k-way relationships? Faloutsos - Pavlo / ore details 3-way and k-way relationships? Rare, but possible: EPLOYEE uses TOOL PROJECT P Faloutsos - Pavlo / ore details 3-way and k-way relationships? Rare, but possible: user reviews keyword App-store/amazon reviews app P Faloutsos - Pavlo /

15 Faloutsos - Pavlo /615 concepts Entities Overview Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo / ore details - attributes key (or primary key): unique identifier underlined, in the ER diagram [not in textbook - FYI: multivalued or set-valued attributes (eg., dependents for EPLOYEE) derived attributes (eg., 15% tip) ] Faloutsos - Pavlo / Overview concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Basic Advanced/ rare Faloutsos - Pavlo /

16 Faloutsos - Pavlo /615 Specialization eg., students: part time (#credithours) and full time (major) ssn name STUDET IS-A major FT-STUDET PT-STUDET #credits Faloutsos - Pavlo / Observations Generalization: exact reverse of specialization attribute inheritance could have many levels of an IS-A hierarchy Faloutsos - Pavlo / ore details Overlap constraints A Covering constraints B C Faloutsos - Pavlo /

17 Faloutsos - Pavlo /615 ore details Overlap constraints can an entity belong to both B and C? Covering constraints can an A entity belong to neither B nor C? B A C Faloutsos - Pavlo / ore details Overlap constraints - examples? A o overlap with overlap A A B C B C B C Faloutsos - Pavlo / ore details Covering constraints - examples? Total coverage A C B B A C Partial coverage A B C Faloutsos - Pavlo /

18 Faloutsos - Pavlo /615 concepts Entities Overview Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo / Aggregation computer model (w/ CPU and HD) and aker (eg., Dell, HP) CPU HD? AKER Faloutsos - Pavlo / Aggregation treat a relationship as an entity used to express a relationship among relationships CPU HD AKER Faloutsos - Pavlo /

19 Faloutsos - Pavlo /615 concepts Entities Overview Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo / Conceptual design Entity vs attribute Entity vs relationship Binary or ternary relationships? Aggregation? Faloutsos - Pavlo / Entity vs. attribute Entity EPLOYEE (w/ emp#, name, job_code,...) Q: How about spouse - entity or attribute? Q: How about dependents? Faloutsos - Pavlo /

20 Faloutsos - Pavlo /615 Entity vs. attribute Entity EPLOYEE (w/ emp#, name, job_code,...) Q: How about spouse - entity or attribute? A: probably, attribute is enough Q: How about dependents? A: Entity - we may have many dependents Faloutsos - Pavlo / Entity vs. Relationship STUDET takes SECTIO OR STUDET 1 TAKES 1 SECTIO Faloutsos - Pavlo / Binary vs Ternary Relationships usually, binary relationships are cleaner : Faloutsos - Pavlo /

21 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships name ssn lot pname age If each policy is owned by just 1 employee: Employees Covers Policies policyid cost Dependents Faloutsos - Pavlo / Binary vs. Ternary Relationships name ssn lot pname age If each policy is owned by just 1 employee: Employees Covers Policies policyid cost Bad design Dependents Faloutsos - Pavlo / Binary vs. Ternary Relationships name ssn lot pname age If each policy is owned by just 1 employee: Key constraint on Policies would mean policy can only cover 1 dependent! Employees Covers Policies policyid cost Bad design Dependents Faloutsos - Pavlo /

22 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships If each policy is owned by just 1 employee: Key constraint on Policies would mean policy can only cover 1 dependent! What are the additional constraints in the 2nd diagram? ssn ssn name Employees Bad design name Employees lot policyid Purchaser Better design Policies cost pname pname Beneficiary Policies Faloutsos - Pavlo / policyid cost lot Covers age Dependents age Dependents Binary vs Ternary Rel. But sometimes ternary rel. can not be replaced by a set of binary rel s: Faloutsos - Pavlo / Binary vs. Ternary Relationships (Contd.) qty Parts Contract Departments Suppliers Parts VS. Departments can-supply Suppliers deals-with why is it bad? Faloutsos - Pavlo /

23 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships (Contd.) qty Parts Contract Departments Suppliers VS. Parts Departments can-supply Suppliers deals-with S can-supply P, D needs P, and D deals-with S does not imply that D has agreed to buy P from S. How do we record qty? Faloutsos - Pavlo / Binary vs. Ternary Relationships (Contd.) qty Parts Contract Departments ot in textbook: in practice, often: Suppliers qty Parts Contract Departments Suppliers Faloutsos - Pavlo / Binary vs. Ternary Relationships (Contd.) ot in textbook: in practice, often: qty c-id Parts Contract Departments Suppliers Faloutsos - Pavlo /

24 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships (Contd.) ot in textbook: in practice, often: qty c-id Parts Contract 1 1 Suppliers Departments Faloutsos - Pavlo / Ternary vs. aggregation use aggregation, if we want to attach a relationship to a relationship (see book for example) (in practice, again we create a unique-id and resort to binary relationships) Faloutsos - Pavlo / Ternary vs. aggregation How would you handle this case? CPU HD AKER Faloutsos - Pavlo /

25 Faloutsos - Pavlo /615 Ternary vs. aggregation How would you handle this case? COP. ODEL CPU HD AKER Faloutsos - Pavlo / Ternary vs. aggregation How would you handle this case? COP. ODEL???? CPU HD AKER Faloutsos - Pavlo / Ternary vs. aggregation How would you handle this case? HAS_CPU CPU COP. ODEL HD AKER Faloutsos - Pavlo /

26 Faloutsos - Pavlo /615 Summary E-R Diagrams: a powerful, user-friendly tool for data modeling: Entities (strong, weak) Attributes (primary keys, discriminators, derived, multivalued) Relationships (1:1, 1:, :; multi-way) Generalization/Specialization; Aggregation Faloutsos - Pavlo / POPULAR Summary E-R Diagrams: a powerful, user-friendly tool for data modeling: Entities (strong, weak) Attributes (primary keys, discriminators, derived, multivalued) Relationships (1:1, 1:, :; multi-way) Generalization/Specialization; Aggregation Faloutsos - Pavlo / Summary - cont d (strong) entity set attribute weak entity set A primary key relationship set A partial key identifying rel. set for weak entity Faloutsos - Pavlo /

27 Faloutsos - Pavlo /615 Summary - cont d cardinalities cardinalities partial/total l:h l :h cardinalities with limits (not in textbook - FYI) Faloutsos - Pavlo / Summary - cont d IS-A aggregation Faloutsos - Pavlo /