Transcript What is a Database Management System?

Database Systems
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Lecture/Workshop: Mon 1-3 LIB 1316; Wed 11 – 12, LH2
Lab: Thu 10-12, ACC, additional help: Mon or Tue?
Judy Cushing - [email protected]
Office Hours: Thursdays 1-2pm, Lab I, 1003, 867-6652
Class web page: off the SOS web page, or
academic.evergreen.edu/r/ricdan16/SOSdatabase/databaseHome.html
• Assignments due most Wednesdays
• Project Parts due Mondays or Thursdays
• Lab Aids: Dan Rice, Jeff Jones
Winter 2002
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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.
Winter 2002
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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.
2.
3.
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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.
Winter 2002
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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.
Winter 2002
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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.
Winter 2002
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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.
Winter 2002
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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>
Winter 2002
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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
Winter 2002
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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
Winter 2002
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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)
Winter 2002
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60’s
Hierarchical
Network
70's
80's
Relational
Choice for most new
applications
90’s
Object Bases
Knowledge Bases
now
Multi-tiered (web) Architectures
Winter 2002
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.
name
ID
Students
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phone
height
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Relationships
• Connect two or more entity sets.
• Represented by diamonds.
Students
Winter 2002
Taking
Courses
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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
…
Winter 2002
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
Winter 2002
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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.
Winter 2002
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Course
Student
Enrolls
LabAid
Student
Ann
Sue
Bob
…
Winter 2002
Course
CS180
CS180
CS180
…
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
Winter 2002
addr
manf
name
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addr
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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
Winter 2002
manf
Drinker
Favorite
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name
addr
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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?
Winter 2002
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Attributes on Relationships
price
Bar
Sells
Beer
• Shorthand for 3-way relationship:
price
Price
Bar
Winter 2002
Sells
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Beer
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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
Winter 2002
TheBar
TheBeer
ThePrice
Bar
Beer
Beer
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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?
Winter 2002
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More Design Issues
1. Subclasses.
2. Keys.
3. Weak entity sets. (Next class.)
Winter 2002
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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.
Winter 2002
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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
Winter 2002
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
Winter 2002
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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
Winter 2002
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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.
Winter 2002
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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.
Winter 2002
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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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general, key at root is key for all.
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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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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.
Winter 2002
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