Transcript Slides01

Database Systems
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Lecture/Workshop: Mon; Wed 10 – 11:30 LIB 1308
Lab: Tue 10-12, ACC, additional help: Thu?
Judy Cushing - [email protected]
Office Hours: Thursdays 9-10, Lab I, 1003, 867-6652
Class web page: off the SOS web page
Assignments due Wednesdays
Project Parts due Mondays
Lab Aid: Peter Keeler
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Textbooks
Required:
• Database Systems: The Complete Book, by Garcia-Molina, Ullman, and
Widom (first edition), Prentice Hall, 2002.
Recommended: (one of these)
• SQL in a Nutshell : A Desktop Quick Reference, Kevin E. Kline, Daniel
Kline, O’Reilly.
• A Guide to the SQL Standard. C. J. Date and H. Darwen, AddisonWesley, 1999. It is more succinct but perhaps a more useful summary,
than the Melton-Simon book.
• SQL3 Complete, A Guide to the SQL Standard: A User's Guide to the
Standard Database Language SQL, (fourth edition), by C.J. Date and
Hugh Darwen, Addison-Wesley, 2000.
• SQL: 1999 - Understanding Relational Language Components, (first
edition), by Melton and Simon, Morgan Kaufmann, 2002.
If you are using PostgreSQL: Books on Unix, Perl, PHP, and CGI,
PostgreSQL: Introduction and Concepts, Bruce Momjian, AddisonWesley, 2001. This might also be on the web.
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Evaluations
I will evaluate you on your ability to design and
implement a database application, and on your
understanding of database concepts. I will
consider:
 Assignments
and in class participation: about 30%.
 Project: about 35%.
 Exams: about 35%.
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Project
• Build an application using a relational database
system (SQL Server or PostgreSQL) accessed via
Java and the web.
• The project has 8 parts (due Mondays or Thursdays),
starting with design and ending with a complete
application.
• The early programming assignments should be
written in SQL, Java.
• Some students found it helpful to switch to
JavaScript, HTML (PHP or Perl if Postgres) for the
web-accessible part.
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Project - tentative schedule
1.
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6.
7.
8.
Project Part 1 due Jan. 14 (Mon) Choose a project and
design an E/R diagram.
Project Part 2 due Jan. 24 (TH) Relational design.
Project Part 3 due Jan. 31 (TH) Create database in
SQLServer.
Project Part 4 due Feb. 7 (TH) Queries, updates, and
indexes.
Project Part 5 due Feb. 21 (TH) Embedded SQL.
Project Part 6 due Feb. 28 (TH) Views, constraints, and
triggers.
Project Part 7 due Mar. 6 (Wed) Entire database
application, in Java.
Project Part 8 due Mar. 11 (Mon) Database application,
accessed via the web.
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Typical Warning
(for those taking this class elsewhere)
• The database class is a lot of work.
• But it is worth it.
• Of all courses you take, it may be the
one that gets you a job….
We know that SOS gets people jobs, but
database expertise does help…. Data
is key to many applications….
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Schedule
• Today: Jan. 7
 Intro,
Entity-Relationship Model.
 Read Chapter 1 and Sections 2.1, 2.3.
• Jan. 9 (W)
 Weak
Entity Sets, Entity-Relationship Design.
 Read Sections 2.2, 2.4.
• Jan. 14 (M)
 Relational Model,
Functional Dependencies.
 Read Sections 3.1-3.5. Project 1 due.
• Jan. 16 (W)
 Normal
Forms, Multivalued Dependencies.
 Read Sections 3.6-3.7. Assignment 1 due.
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Syllabus
• The background and history of database
management systems.
• The fundamentals of using a database
management systems.
• Industry standards used for database management
systems.
• Theoretical background of the relational model.
• Queries and Updates.
• Logic databases? Constraints and Triggers.
• Transactions and Security.
• Object-oriented, object-relational, semi-structured
and XML database systems.
• Mediation and warehousing.
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What is a Database Management System?
1. Manages very large amounts of data.
2. Supports efficient access to very large amounts
of data.
3. Supports concurrent access to very large
amounts of data.
 Example:
bank and its ATM machines.
4. Supports secure, atomic access to very large
amounts of data.
 Contrast
two people editing the same UNIX file – last to write
“wins” – with the problem if two people deduct money from
the same account via ATM machines at the same time – new
balance is wrong whichever writes last.
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Relational Model
• Based on tables, as:
acct #
12345
34567
…
name
Sally
Sue
…
balance
1000.21
285.48
…
• Today used in most DBMS's.
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The DBMS Marketplace
• Relational DBMS companies – Oracle, Sybase – are among the
largest software companies in the world.
• IBM offers its relational DB2 system. With IMS, a nonrelational
system, IBM is by some accounts the largest DBMS vendor in the
world.
• Microsoft offers SQL-Server, plus Microsoft Access for the cheap
DBMS on the desktop, answered by “lite” systems from other
competitors.
• Relational companies also challenged by “object-oriented DB”
companies, and XML data stores.
• But countered with “object-relational” systems, which retain the
relational core while allowing type extension as in OO systems.
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Three Aspects to Studying DBMS's
1. Modeling and design of databases.

Allows exploration of issues before committing to an
implementation.
2. Programming: queries and DB operations like
update.

SQL = “intergalactic dataspeak.”
3. DBMS implementation.
Consider DBMS system components, p. 11.
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Query Languages
Employee
Name
Department
Dept
Dept
Manager
SQL
SELECT Manager
FROM Employee, Department
WHERE Employee.name = "Clark Kent”
AND Employee.Dept = Department.Dept
Query Language
Data definition language (DDL) ~ like type defs in C or Pascal
Data Manipulation Language (DML)
Query (SELECT)
UPDATE < relation name >
SET <attribute> = < new-value>
WHERE <condition>
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Host Languages
C, C++, Fortran, Lisp, COBOL
Application prog.
Calls to
DB
DBMS
Local Vars
(Memory)
(Storage)
Host language is completely general (Turing complete)
but gives you no support
Query language—less general "non procedural" and
optimizable
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Relational model is good for:
Large amounts of data —> simple operations
Navigate among small number of relations
Difficult Applications for relational model:
• VLSI Design (CAD in general)
• CASE
• Graphical Data
ALU
ADDER
A
FA
CPU
Adder
ALU
ADDER
Bill of Materials or
transitive closure
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Where number of "relations" is large, relationships are complex
• Object Data Model
• Logic Data Model
OBJECT DATA MODEL
1.
2.
3.
4.
Complex Objects – Nested Structure (pointers or
references)
Encapsulation, set of Methods/Access functions
Object Identity
Inheritance – Defining new classes like old classes
Object model: usually find objects via explicit navigation
Also query language in some systems
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LOGIC (Horn Clause) DATA MODEL
• Prolog, Datalog
if A1 and A2 then B
prolog B:- A1 and A2
Functions s(5) = 6 (successor)
Predicates with Arguments sum(X,Y,Z)
X+Y=Z
sum(X,0,X) means X + 0 = X (always true for all X)
sum(X,s(Y),s(Z)):-sum(X,Y,Z)
means X+(Y+1) = (Z+1) if X + Y = Z
More power than relational
Can Compute Transitive Closure
edge(X,Y)
path(X,Y) :- edge(X,Y)
path(X,Z) :- path(X,Y) & edge(Y,Z)
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60’s
Hierarchical
Network
70's
80's
Choice for most new
applications
Relational
90’s
Object Bases
Knowledge Bases
now
Multi-tiered (web) Architectures
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XML Data Transfers and Transformations
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Entity/Relationship Model
Diagrams to represent designs.
• Entity like object = “thing.”
• Entity set like class = set of “similar”
entities/objects.
• Attribute = property of entities in an entity set,
similar to fields of a struct.
• In diagrams, entity set  rectangle;
attribute  oval.
ID
name
Students
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height
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Relationships
• Connect two or more entity sets.
• Represented by diamonds.
Students
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Relationship Set
Think of the “value” of a relationship set as a table.
• One column for each of the connected entity sets.
• One row for each list of entities, one from each
set, that are connected by the relationship.
Students
Sally
Sally
Joe
…
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Courses
CS180
CS111
CS180
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Multiway Relationships
Usually binary relationships (connecting two E.S.) suffice.
• However, there are some cases where three or more E.S.
must be connected by one relationship.
• Example: relationship among students, courses, Lab
Aids.
Student
Taking
Course
Possibly, this E/R diagram is OK:
Assisting
Lab Aid
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• Works in CS180, because each Lab Aid
works for all students. Connection studentLabAid is only via the course.
• But what if students were divided into
sections, each headed by a LabAid?
Then,
a student in CS180 would be related to
only one of the LabAids for CS180. Which
one?
• Need a 3-way relationship to tell.
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Course
Student
Enrolls
LabAid
Student
Ann
Sue
Bob
…
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CS180
CS180
CS180
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LabAid
Jan
Pat
Jan
…
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Beers-Bars-Drinkers Example
• Our running example for the course.
name
license
Serves
Bar
Frequents
Beer
Likes
Drinker
name
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addr
manf
name
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Multiplicity of Relationships
Many-many
Many-one
One-one
Representation of Many-One
• E/R: arrow pointing to “one.”
Rounded
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arrow = “exactly one.”
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Example:
Drinkers Have Favorite Beers
name
Serves
addr
license
Bar
Frequents
Likes
Beer
name
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manf
Drinker
Favorite
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One-One Relationships
Put arrows in both directions.
Manufacturer
Bestseller
Beer
Design Issue:
Is the rounded arrow justified?
Design Issue:
Here, manufacturer is an E.S.
In earlier diagrams it is an attribute.
Which is right?
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Attributes on Relationships
price
Bar
Sells
Beer
• Shorthand for 3-way relationship:
price
Price
Bar
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• A true 3-way relationship.
Price
depends jointly on beer and bar.
• Notice arrow convention for multiway
relationships: “all other E.S. determine one
of these.”
Not
sufficiently general to express any
possibility.
However, if price, say, depended only on the
beer, then we could use two 2-way
relationships: price-beer and beer-bar.
Or better: just make price an attribute of beer.
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Converting Multiway to 2-Way
• Baroque in E/R, but necessary in certain “object-oriented” models.
• Create a new connecting E.S. to represent rows of a relationship
set.

E.g., (Joe's Bar, Bud, $2.50) for the Sells relationship.
• Many-one relationships from the connecting E.S. to the others.
BBP
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TheBar
TheBeer
ThePrice
Bar
Beer
Price
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Roles
Sometimes an E.S. participates more than
once in a relationship.
• Label edges with roles to distinguish.
Married
husband
wife
Husband
d1
d3
…
Wife
d2
d4
…
Drinker
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Buddies
1
2
Drinker
Buddy1
d1
d1
d2
d2
…
Buddy2
d2
d3
d1
d4
…
• Notice Buddies is symmetric, Married not.
No
way to say “symmetric” in E/R.
Design Question
Should we replace husband and wife by one
relationship spouse?
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More Design Issues
1. Subclasses.
2. Keys.
3. Weak entity sets. (Next class.)
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Subclasses
Subclass = special case = fewer entities =
more properties.
• Example: Ales are a kind of beer. In
addition to the properties (= attributes and
relationships) of beers, there is a “color”
attribute for ales.
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E/R Subclasses
• Assume subclasses form a tree (no multiple
inheritance).
• isa triangles indicate the subclass relation.
name
Beer
manf
isa
color
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Ale
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Different Subclass Viewpoints
1. E/R viewpoint: An entity has a component in each entity set
to which it logically belongs.
 Its
properties are the union of the properties of these E.S.
2. Contrasts with object-oriented viewpoint: An object (entity)
belongs to exactly one class.
 It
inherits properties
of its superclasses.
name
Beer
isa
color
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manf
Pete’s Ale
Ale
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Multiple Inheritance
Theoretically, an E.S. could be a subclass of
several other entity sets.
name
manf
name
manf
Beers
Wines
isa
isa
Grape
Beers
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Problems
How should conflicts be resolved?
• Example: manf means vintner for wines,
bottler for beers. What does manf mean for
“grape beers”?
• Need ad-hoc notation to resolve meanings.
• In practice, we shall assume a tree of entity
sets connected by isa, with all “isas”
pointing from child to parent.
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Keys
A key is a set of attributes whose values can
belong to at most one entity.
• In E/R model, every E.S. must have a key.
It
could have more than one key, but one set of
attributes is the “designated” key.
• In E/R diagrams, you should underline all
attributes of the designated key.
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Example
• Suppose name is key for Beers.
name
Beers
manf
isa
color
Ales
• Beer name is also key for ales.
 In
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Example: A Multiattribute Key
number
dept
hours
Courses
room
• Possibly, the combination of hours + room
also forms a key, but we have not
designated it as such.
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In Class exercise (if time)
or
Assignment for Wednesday
(for those who did SOS this Fall)
Convert the UML for EU-Bid and EU-Lease
to an ER diagram.
Merge them into a design for one database.
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