Administrivia. Carnegie Mellon Univ. Dept. of Computer Science /615 - DB Applications. Course Topics. Problem

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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 Administrivia Course url: Course policies Foils in pps: Faloutsos - Pavlo /615 2 Introduction to DBSs Data odels Query Language (SQL) Course Topics Database Design Query Optimization & Indexing Transaction anagement Advanced Topics 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 3 Faloutsos - Pavlo /

2 Faloutsos - Pavlo /615 Database users naive users casual users application programmers [ DBA (Data base administrator)] select * from student DBS data Casual users and meta-data = catalog Faloutsos/Pavlo /615 5 Faloutsos/Pavlo /615 6 Pictorially: DBS data ``aive users app. (eg., report generator) and meta-data = catalog Authors of applications (like the report generator ) DBS data App. programmers app. (eg., report generator) and meta-data = catalog Faloutsos/Pavlo /615 7 Faloutsos/Pavlo /

Faloutsos - Pavlo 15-415/615 Duties? DB Administrator (DBA) Duties?

3 Faloutsos - Pavlo /615 Duties? DB Administrator (DBA) Duties? DB Administrator (DBA) DBS and meta-data = DBS and meta-data = data catalog data catalog Faloutsos/Pavlo /615 9 Faloutsos/Pavlo / DB Administrator (DBA) schema definition ( logical level) physical schema (storage structure, access methods schema modifications granting authorizations integrity constraint specification 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 / Faloutsos - Pavlo /

4 Faloutsos - Pavlo /615 Database users naive users casual users application programmers [ DBA (Data base administrator)] Database Design Requirements Analysis Conceptual Design Logical Design Schema Refinement Physical Design Security Design Faloutsos/Pavlo / Faloutsos - Pavlo / 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 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 / Faloutsos - Pavlo /

5 Faloutsos - Pavlo /615 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 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 / Faloutsos - Pavlo / 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 / 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 /

6 Faloutsos - Pavlo /615 otivation & upcoming conclusion: Overview E-R diagrams are excellent documentation tools Student concepts Entities Relationships Basic 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); Takes Course Attributes Specialization/Generalization Aggregation ER modeling questions Advanced/ rare Faloutsos - Pavlo / Faloutsos - Pavlo / Tools Student Takes Example Entities ( entity sets ) Relationships ( rel. sets ) Course Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section P and mapping constraints attributes nouns -> entity sets verbs -> relationship sets Faloutsos - Pavlo / Faloutsos - Pavlo /

7 Faloutsos - Pavlo /615 Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section Example Students, taking courses, offered by instructors; a course may have multiple sections; one instructor per section nouns -> entity sets verbs -> relationship sets nouns -> entity sets verbs -> relationship sets Faloutsos - Pavlo / Faloutsos - Pavlo / name name ssn STUDET ssn STUDET c-id c-name COURSE ISTRUCTOR issn primary key = unique identifier -> underline Faloutsos - Pavlo / issn ISTRUCTOR but: sections of course (with different instructors)? Faloutsos - Pavlo /

8 Faloutsos - Pavlo /615 ssn STUDET ssn STUDET c-id c-id s-id SECTIO COURSE s-id SECTIO COURSE issn ISTRUCTOR but: s-id is not unique... (see later) issn ISTRUCTOR Q: how to record that students take courses? Faloutsos - Pavlo / Faloutsos - Pavlo / ssn STUDET STUDET takes c-id takes c-id s-id SECTIO COURSE s-id SECTIO COURSE issn ISTRUCTOR teaches 1 ISTRUCTOR Faloutsos - Pavlo / Faloutsos - Pavlo /

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

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

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

12 Faloutsos - Pavlo /615 Weak entities Weak entities weak entities: if they need to borrow a unique id from a strong entity - thick box. Other example(s) of weak entities? c-id + s-id : unique id for SECTIO partial key (eg., s-id ) - dashed-underline identifying relationship (eg., has ) c-id id s-id SECTIO 1 has COURSE 1?? Faloutsos - Pavlo / Faloutsos - Pavlo / Weak entities Other example(s) of weak entities? ore details self-relationships - example? e-id name Dependent 1 has Employee Faloutsos - Pavlo / Faloutsos - Pavlo /

13 Faloutsos - Pavlo /615 ore details ore details self-relationships - example? self-relationships - example? 1 manages Has-friend EPLOYEE FB user Faloutsos - Pavlo / Faloutsos - Pavlo / ore details 3-way and k-way relationships? ore details 3-way and k-way relationships? Rare, but possible: EPLOYEE uses TOOL PROJECT P Faloutsos - Pavlo / Faloutsos - Pavlo /

14 Faloutsos - Pavlo /615 ore details 3-way and k-way relationships? Rare, but possible: ore details 3-way and k-way relationships? Rare, but possible: user reviews keyword P P Other cases? App-store/amazon reviews app Faloutsos - Pavlo / Faloutsos - Pavlo / concepts Entities Relationships Overview Attributes Specialization/Generalization Aggregation ER modeling questions 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 / Faloutsos - Pavlo /

15 Faloutsos - Pavlo /615 concepts Entities Relationships Overview Attributes Specialization/Generalization Aggregation ER modeling questions Basic Advanced/ rare eg., students: part time (#credithours) and full time (major) major Specialization ssn name FT-STUDET STUDET IS-A PT-STUDET Faloutsos - Pavlo / #credits Faloutsos - Pavlo / Observations ore details Generalization: exact reverse of specialization attribute inheritance could have many levels of an IS-A hierarchy Overlap constraints Covering constraints B A C Faloutsos - Pavlo / Faloutsos - Pavlo /

16 Faloutsos - Pavlo /615 ore details 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 A Overlap constraints - examples? o overlap B C A with overlap B C B A C Faloutsos - Pavlo / Faloutsos - Pavlo / ore details Overview Covering constraints - examples? Total coverage A C B Partial coverage A C B B A C concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo / Faloutsos - Pavlo /

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

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

19 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships name ssn lot pname age Binary vs. Ternary Relationships name ssn lot pname age If each policy is owned by just 1 employee: Employees Covers Policies policyid cost Dependents If each policy is owned by just 1 employee: Employees Bad design Covers Policies policyid cost Dependents Faloutsos - Pavlo / Faloutsos - Pavlo / 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! ssn name Employees Bad design policyid Covers Policies cost pname Faloutsos - Pavlo / lot age Dependents 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 19

20 Faloutsos - Pavlo /615 Binary vs Ternary Rel. Binary vs. Ternary Relationships (Contd.) qty But sometimes ternary rel. can not be replaced by a set of binary rel s: Parts Contract Suppliers Departments VS. Parts Departments can-supply Suppliers deals-with why is it bad? Faloutsos - Pavlo / Faloutsos - Pavlo / Binary vs. Ternary Relationships (Contd.) qty Binary vs. Ternary Relationships (Contd.) qty Parts Contract Suppliers Departments VS. Parts Contract Suppliers Departments ot in textbook: in practice, often: Parts Departments qty can-supply Suppliers deals-with Parts Contract Departments 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 / Suppliers Faloutsos - Pavlo /

Faloutsos - Pavlo 15-415/615 Binary vs. Ternary Relationships (Contd.

21 Faloutsos - Pavlo /615 Binary vs. Ternary Relationships (Contd.) Binary vs. Ternary Relationships (Contd.) ot in textbook: ot in textbook: in practice, often: in practice, often: qty c-id qty c-id Parts Contract Departments Parts Contract Departments 1 1 Suppliers Suppliers Faloutsos - Pavlo / Faloutsos - Pavlo / Ternary vs. aggregation 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) How would you handle this case? CPU HD AKER Faloutsos - Pavlo / Faloutsos - Pavlo /

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

23 Faloutsos - Pavlo /615 Summary Summary - cont d POPULAR 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 (strong) entity set weak entity set relationship set identifying rel. set for weak entity A A attribute primary key partial key Faloutsos - Pavlo / Faloutsos - Pavlo / Summary - cont d Summary - cont d cardinalities cardinalities IS-A partial/total l:h l :h cardinalities with limits aggregation (not in textbook - FYI) Faloutsos - Pavlo / Faloutsos - Pavlo /

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

Carnegie Mellon Univ. Dept. of Computer Science /615 - DB Applications. Problem. Faloutsos - Pavlo CMU SCS /615 Faloutsos - Pavlo 15-415/615 Carnegie ellon Univ. Dept. of Computer Science 15-415/615 - DB Applications C. Faloutsos - A. Pavlo Lecture#2: E-R diagrams Problem Develop an application for U.G. admin: Student