Faloutsos - Pavlo C. Faloutsos - A. Pavlo Lecture#2: E-R diagrams CMU SCS 15-415/615 Carnegie Mellon 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: How do you proceed? Faloutsos - Pavlo CMU SCS 15-415/615 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 CMU SCS 15-415/615

Database Design Requirements Analysis Conceptual Design Logical Design Faloutsos - Pavlo CMU SCS 15-415/615 Database Design Requirements Analysis Conceptual Design Logical Design Schema Refinement Physical Design Security Design Faloutsos - Pavlo CMU SCS 15-415/615

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

Problem’ Maintain Develop an application for U.G. admin: Faloutsos - Pavlo CMU SCS 15-415/615 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: Faloutsos - Pavlo CMU SCS 15-415/615

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

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? Faloutsos - Pavlo CMU SCS 15-415/615

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? Faloutsos - Pavlo CMU SCS 15-415/615

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 Faloutsos - Pavlo CMU SCS 15-415/615

Motivation & upcoming conclusion: E-R diagrams are excellent documentation tools Student Course Takes Faloutsos - Pavlo CMU SCS 15-415/615

Overview concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo CMU SCS 15-415/615

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

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 CMU SCS 15-415/615

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 CMU SCS 15-415/615

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 CMU SCS 15-415/615

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

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

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

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

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

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

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

Cardinalities 1 to 1 (example?) 1 to N N to M 1 1 1 N N M Faloutsos - Pavlo CMU SCS 15-415/615

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

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

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

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

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

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

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

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

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

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

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 SECTION partial key (eg., ‘s-id’) - dashed-underline identifying relationship (eg., ‘has’) c-id N 1 s-id SECTION has COURSE Faloutsos - Pavlo CMU SCS 15-415/615

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

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

More details self-relationships - example? ?? ?? ?? ?? Faloutsos - Pavlo CMU SCS 15-415/615

More details self-relationships - example? manages 1 EMPLOYEE N Faloutsos - Pavlo CMU SCS 15-415/615

More details self-relationships - example? Has-friend ?? FB user ?? Faloutsos - Pavlo CMU SCS 15-415/615

More details 3-way and k-way relationships? Faloutsos - Pavlo CMU SCS 15-415/615

More details 3-way and k-way relationships? Rare, but possible: N M EMPLOYEE TOOL uses P PROJECT Faloutsos - Pavlo CMU SCS 15-415/615

More details 3-way and k-way relationships? Rare, but possible: N M ?? Other cases? ?? Faloutsos - Pavlo CMU SCS 15-415/615

More details 3-way and k-way relationships? Rare, but possible: N M reviews user keyword P App-store/amazon reviews app Faloutsos - Pavlo CMU SCS 15-415/615

Overview concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo CMU SCS 15-415/615

More 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 EMPLOYEE) derived attributes (eg., 15% tip) ] Faloutsos - Pavlo CMU SCS 15-415/615

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

Specialization eg., students: part time (#credit-hours) and full time (major) name STUDENT ssn IS-A FT-STUDENT PT-STUDENT major #credits Faloutsos - Pavlo CMU SCS 15-415/615

Observations Generalization: exact reverse of ‘specialization’ attribute inheritance could have many levels of an IS-A hierarchy Faloutsos - Pavlo CMU SCS 15-415/615

More details Overlap constraints Covering constraints A B C Faloutsos - Pavlo CMU SCS 15-415/615

More details Overlap constraints Covering constraints can an entity belong to both ‘B’ and ‘C’? Covering constraints can an ‘A’ entity belong to neither ‘B’ nor ‘C’? B C Faloutsos - Pavlo CMU SCS 15-415/615

More details Overlap constraints - examples? A No overlap with overlap B C A A C C B B Faloutsos - Pavlo CMU SCS 15-415/615

More details Covering constraints - examples? A Total coverage A C B B Partial coverage A C B Faloutsos - Pavlo CMU SCS 15-415/615

Overview concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo CMU SCS 15-415/615

Aggregation computer model (w/ CPU and HD) and Maker (eg., Dell, HP) M ? MAKER HD CPU Faloutsos - Pavlo CMU SCS 15-415/615

Aggregation treat a relationship as an entity used to express a relationship among relationships CPU HD N M MAKER Faloutsos - Pavlo CMU SCS 15-415/615

Overview concepts Entities Relationships Attributes Specialization/Generalization Aggregation ER modeling questions Faloutsos - Pavlo CMU SCS 15-415/615

Conceptual design Entity vs attribute Entity vs relationship Binary or ternary relationships? Aggregation? Faloutsos - Pavlo CMU SCS 15-415/615

Entity vs. attribute Entity EMPLOYEE (w/ emp#, name, job_code, ...) Q: How about ‘spouse’ - entity or attribute? Q: How about ‘dependents’? Faloutsos - Pavlo CMU SCS 15-415/615

Entity vs. attribute Entity EMPLOYEE (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 CMU SCS 15-415/615

Entity vs. Relationship STUDENT STUDENT 1 N N OR takes TAKES M N SECTION 1 SECTION Faloutsos - Pavlo CMU SCS 15-415/615

Binary vs Ternary Relationships usually, binary relationships are ‘cleaner’: Faloutsos - Pavlo CMU SCS 15-415/615

Binary vs. Ternary Relationships Faloutsos - Pavlo CMU SCS 15-415/615 age pname Dependents Covers name Employees ssn lot If each policy is owned by just 1 employee: Policies policyid cost Faloutsos - Pavlo CMU SCS 15-415/615 7

Binary vs. Ternary Relationships Faloutsos - Pavlo CMU SCS 15-415/615 Policies policyid cost age pname Dependents Covers name Employees ssn lot If each policy is owned by just 1 employee: Bad design Faloutsos - Pavlo CMU SCS 15-415/615 7

Binary vs. Ternary Relationships Faloutsos - Pavlo CMU SCS 15-415/615 Policies policyid cost age pname Dependents Covers name Employees ssn lot If each policy is owned by just 1 employee: Bad design Key constraint on Policies would mean policy can only cover 1 dependent! Faloutsos - Pavlo CMU SCS 15-415/615 7

Binary vs. Ternary Relationships Faloutsos - Pavlo CMU SCS 15-415/615 Policies policyid cost age pname Dependents Covers name Employees ssn lot If each policy is owned by just 1 employee: Bad design Key constraint on Policies would mean policy can only cover 1 dependent! Beneficiary age pname Dependents policyid cost Policies Purchaser name Employees ssn lot Better design What are the additional constraints in the 2nd diagram? Faloutsos - Pavlo CMU SCS 15-415/615 7

Binary vs Ternary Rel. But sometimes ternary rel. can not be replaced by a set of binary rel’s: Faloutsos - Pavlo CMU SCS 15-415/615

Binary vs. Ternary Relationships (Contd.) Faloutsos - Pavlo CMU SCS 15-415/615 Binary vs. Ternary Relationships (Contd.) qty Parts Contract Departments VS. Suppliers Parts Departments can-supply Suppliers deals-with why is it bad? Faloutsos - Pavlo CMU SCS 15-415/615 9

Binary vs. Ternary Relationships (Contd.) Faloutsos - Pavlo CMU SCS 15-415/615 Binary vs. Ternary Relationships (Contd.) qty Parts Contract Departments VS. Suppliers 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 CMU SCS 15-415/615 9

Binary vs. Ternary Relationships (Contd.) Faloutsos - Pavlo CMU SCS 15-415/615 Binary vs. Ternary Relationships (Contd.) qty Not in textbook: in practice, often: Parts Contract Departments Suppliers qty Parts Contract Departments Suppliers Faloutsos - Pavlo CMU SCS 15-415/615 9

Binary vs. Ternary Relationships (Contd.) Faloutsos - Pavlo CMU SCS 15-415/615 Binary vs. Ternary Relationships (Contd.) Not in textbook: in practice, often: c-id qty Parts Contract Departments Suppliers Faloutsos - Pavlo CMU SCS 15-415/615 9

Binary vs. Ternary Relationships (Contd.) Faloutsos - Pavlo CMU SCS 15-415/615 Binary vs. Ternary Relationships (Contd.) Not in textbook: in practice, often: c-id qty M N Parts Contract Departments N N 1 1 Suppliers Faloutsos - Pavlo CMU SCS 15-415/615 9

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 CMU SCS 15-415/615

Ternary vs. aggregation How would you handle this case? CPU HD N M MAKER Faloutsos - Pavlo CMU SCS 15-415/615

Ternary vs. aggregation How would you handle this case? COMP. MODEL MAKER HD CPU Faloutsos - Pavlo CMU SCS 15-415/615

Ternary vs. aggregation How would you handle this case? COMP. MODEL ? ? ? ? MAKER HD CPU Faloutsos - Pavlo CMU SCS 15-415/615

Ternary vs. aggregation How would you handle this case? COMP. MODEL M M HAS_CPU N N MAKER HD CPU Faloutsos - Pavlo CMU SCS 15-415/615

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:N, N:M; multi-way) Generalization/Specialization; Aggregation Faloutsos - Pavlo CMU SCS 15-415/615

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:N, N:M; multi-way) Generalization/Specialization; Aggregation POPULAR Faloutsos - Pavlo CMU SCS 15-415/615

Summary - cont’d attribute (strong) entity set weak entity set primary key A relationship set partial key A identifying rel. set for weak entity Faloutsos - Pavlo CMU SCS 15-415/615

Summary - cont’d M N cardinalities cardinalities l’:h’ l:h with limits l:h l’:h’ partial/total (not in textbook - FYI) Faloutsos - Pavlo CMU SCS 15-415/615

Summary - cont’d IS-A aggregation Faloutsos - Pavlo CMU SCS 15-415/615