EECS 339 Lecture 3

NormalizationDatabase Internals

Hobby SchemaSSN Name Address Hobby Cost

123 john main st dolls $

123 john main st bugs $

345 mary lake st tennis $$

456 joe first st dolls $

“Wide” schema – has redundancy and anomalies in the presence of updates, inserts, and deletes

Table key is Hobby, SSN

PersonPerson HobbyHobby

SSN

Address

Name

Name

Cost

n:n

Entity Relationship Diagram

BCNFify Example for Hobbies

Schema FDs

(S,H,N,A,C) S,H N,A,CS N, AH C

S = SSN, H = Hobby, N = Name, A = Addr, C = Cost

violates bcnf

Schema FDs

(S, N,A) S N, A

Schema FDs

(S,H, C) S,H CH C

violates bcnf

Schema FDs

(H, C) H C

Schema FDs

(S,H)

Iter 1

Iter 2

key

Iter 3

Non-BCNF ExampleAccount Client Office

A Joe 1

B Mary 1

A John 1

C Joe 2

Primary Key is Client, OfficeEach Account is handled by exactly 1 OfficeWithin a given Office, a given Client has exactly 1 Account

Violates BCNF! (account not a superkey)

FDs:Client, Office AccountAccount Office

Splitting into 1. Account,Office and2. Client

Loses correspondence between clients, offices, and accounts

Redundancy!

Third Normal Form vs. BCNF

• This is a minimal example of a table in “third normal form” (3NF) but not BCNF

• All tables in BCNF are also in 3NF• But 3NF allows redundancy to “preserve FDs”

– Meaning that all FDs can be checked in a single table

Account Client Office

A Joe 1

B Mary 1

A John 1

C Joe 2

FDs:Client, Office AccountAccount Office

Study Break• Patient database• Want to represent patients at hospitals with doctors• Patients have names, birthdates• Doctors have names, specialties• Hospitals have names, addresses• One doctor can treat multiple patients, each patient has one doctor• Each patient in one hospital, hospitals have many patients• Doctors work for one hospital, hospitals have many doctors

1) Draw an ER diagram

2) What are the functional dependencies?

3) What is the normalized schema? Is it in BCNF?

Study Break (cont’d)

• Write a SQL statement for:– Getting the names of all patients seeing Dr. X– Determining the average # of patients per hospital– Tallying up the # of doctors practicing each

specialty at each hospital

Database Internals OutlineFront End

Admission ControlConnection Management

(sql)Parser

(parse tree)Rewriter

(parse tree) Planner & Optimizer

(query plan) Executor

Query System

Storage System

Access MethodsLock ManagerBuffer ManagerLog Manager