Announcements

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Announcements

• Midterm is Nov. 22 (815am 945am)
• Covers until the end of Normalization
• You answer in the same exam paper
• Closed-Book, One sheet is allowed for your notes

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Revision

• Instructor Mohamed Eltabakh
• meltabakh_at_cs.wpi.edu

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Covered Topics

• Entity-Relationship Model ERD
• Relational Model
• Relational Algebra
• Functional Dependencies Normalization

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Relational Algebra
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Key Points

• Understand the meaning of each operator and what
  it does, E.g.,
• Selection (sc) selects certain tuples based on a
  condition (all columns)
• Projection (pk) selects certain columns (All
  tuples)
• Join (?C) joins tuples from one relation with
  another relation based on a condition
• Practice how to combine these operators to answer
  queries
• Performance rules
• Apply selection earlier whenever possible
• Use joins instead of Cartesian product
• Avoid un-necessary joins

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Relational Algebra Exercise
ShipClass(name, type, country, numGuns,
designYear, weight) WarShips(shipName,
className, builtYear) Missions(missionName,
date) Results(shipName, missionName, status)

• Ships having the same design belong to the same
  class. The class information is stored in
  ShipClass. The ship information is stored in
  WarShips
• Each ship may participate in multiple missions.
  The mission information is stored in Missions
• Each ship in a mission has a status as either
  damaged, sunk, or ok. This information is
  stored in Results

Write the algebraic expression for the following
queries
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Query 1
For classes with at least 10 guns, report the
class name and country
pname,country (snumGuns gt 10(ShipClass))
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Query 2
List the warShips built after 1932
sbuiltYear gt 1932(WarShips)
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Query 3
Report the names of ships damaged in the mission
of Sun Rising.
pshipName (smissionName Sun Rising AND
statusdamaged (Results))
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Query 4
Suppose there was an agreement prohibiting
war-ships heavier than 40,000 tons. Report the
ship names and built year of ships violating this
agreement.
pshipName,builtYear (sweight gt 40,000(ShipClass
?nameclassName WarShips))
pshipName,builtYear (sweight gt 40,000(ShipClass)
?nameclassName WarShips)
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Query 5
R1 ?pID(sFirstName John AND
LastNameSmith(Doctor) ?SSNDoctor_SSN
Prescription) R2 ?pID?Prescription_id(sTradeName
Aspirin(Prescription_Medicine)) n R1 Result ?
?(pPateint_SSN( R2 ? Prescription))
Continue from the previous query, Find the ships
that violate the agreement the least (i.e., the
lightest ships violating the agreement)
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Query 6
In the mission of Sun Rising, find the name and
weight of the ships involved
R1 ?pshipName(smissionName Sun
Rising(Results)) Result ? pR1.shipName, weight
(R1 ?R1.shipNameWarships.shipName WarShips

?classNamename ShipClass)
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Query 7
Report ship name for ships that were ok in one
mission, but later sunk in another.
pshipName(sstatus sunk(Results)) n

pshipName(sstatus ok(Results))
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ER Relational Models
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Key Points

• Remember the notations used in ERD
• Relationships cardinalities (1-1, 1-M, M-M)
• Entity sets and weak entity sets
• Primitive, derived, and composite attributes
• Mapping rules from ERD to relational model, E.g.,
• M-M relationship ? separate table
• 1-M relationship ? take the key from the one-side
  to the many-side
• 1-1 relationship ? take the key from either sides
  to the other side
• ISA relationship ? Many choices depending on its
  type
• Remember to indicate the integrity constraints,
  most important are
• Primary keys, Foreign keys

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Airline Application

• We have a set of planes, each plane can make many
  flights.
• Each plane has properties such as ID (unique
  identifier), model, capacity, year in which it is
  built, and weight
• Each flight has a departure city, arrival city,
  and it can make transit in many other cities.
  Also each flight has the departure date, arrival
  date, and the transit date in each of the transit
  cities (assume the date captures both the date
  and exact time).
• Each flight has some properties such as
  FlightNum (unique identifier), number of transit
  stops, number of passengers
• For each city, we have an CityID (unique
  identifier), name, and country

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Question 1

• Design an ER diagram for the given application.
  The diagram must include
• The entity sets, attributes, primary keys
• The relationships with the correct cardinalities
• State any assumptions that you make and affect
  your design

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Assumption The entire flight is done by a single
plane
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Question 2

• Extend your ERD in the previous question to
  capture the following additional requirements
• Each flight has one captain, one assistant
  captain, and between 2 to 4 flight attendants
• Each of the captain, assistant captain, and
  attendants have a common set of properties such
  as EmployeeID (unique identifier), name, salary,
  and DoB
• The same person can be captain on some flights
  and assistant captain on other flights (basically
  same person can have different roles (captain or
  assistant captain) in different flights).

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(No Transcript)
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Question 3

• Map the ERD from the previous question (Question
  2) to the corresponding relational model
• Provide the CREATE TABLE commands with the field
  names and appropriate data types
• Identify the primary keys and foreign keys in the
  relations

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Relational Model
Create Table Employee ( ID int Primary
Key, name varchar(100), DOB int, Salary
int, JobTitle varchar(100) check
JonTitle in (Captain, Attendant))
Create Table Plane ( ID int Primary Key, Year
int, Capacity int, Weight int, Model
varchar(50))
Create Table City( ID int Primary Key, Name
varchar(100), Country varchar(100))
Create Table Flight( FNum varchar(8) Primary
Key, NumStops int, NumPassengers int, PlaneID
int Foreign Key References Plane(ID), ArrivalCityI
D int Foreign Key References City(CityID), Depart
CityID int Foreign Key References
City(CityID), ArrivalDate date, DepartDate
date, CaptainID int Foreign Key References
Employee (ID), AssistID int Foreign Key
References Employee (ID))
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Relational Model (Contd)
Create Table Transit ( FNum int Foreign Key
References Flight(FNum), CityID int Foreign Key
References City(CityID), TransitDate
date, Primary Key (Fnum, CityID))
Create Table Flight_Attendant( FNum int Foreign
Key References Flight(FNum), AttendantID int
Foreign Key References Employee(ID), Primary Key
(Fnum, EmpID))
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Relational Model (Contd)

• Assumptions
• The ISA relationship is modeled using one table
  Employee
• Whether the employee is Captain or Attendant is
  modeled using a new attribute JobTitle
• Business Constraints
• Attributes CaptainID and AssistID in Flight
  must correspond to employee with job title
  Captain
• Attribute AttendantID in Flight_Attendant must
  correspond to employee with job title Attendant
• Attribute NumPassengers in Flight must be less
  than or equal to attribute Capacity in Plane

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Functional Dependencies Normalization
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Key Points

• Identifying the candidate keys of relations
• Use of Transitive, and Union properties to
  generate more FDs
• Computing the attribute closure
• A is a key if all attributes are in its closure
• A candidate key is also a super key (But it is
  minimal)
• Remember the rules for BCNF and 3NF
• Test which FD is violating the rules
• Decompose based on this rule

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Question 1

• Given relation R (A, B, C, D, E) with the
  following FDs
• F AB ? C, C ? D, B?D, CD ? E, AB ? E
• Compute the canonical (minimal) cover of F G
• What are the candidate keys of R?

G AB ? C, C ? DE, B?D
AB
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Question 2

• Given relation R (A, B, C, D) with the
  following FDs
• F B ? C, B ?D
• What are the candidate keys of R?
• Report FDs violating BCNF (if any)?
• Decompose R to be in BCNF (if not already)?

AB
B ? C B ? D
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Question 2 (Contd)

• Given relation R (A, B, C, D) with the
  following FDs
• F B ? C, B ?D
• What are the candidate keys of R?
• Report FDs violating 3NF (if any)?
• Decompose R to be in 3NF (if not already)?

AB
B ? C B ? D