Download Database Application Design

January 28, 2000
Database Application Design
Handout #4
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University of Michigan
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Course information
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Instructor: Dragomir R. Radev ([email protected])
Office: 305A, West Hall
Phone: (734) 615-5225
Office hours: Thursdays 3-4 and Fridays 1-2
Course page: http://www.si.umich.edu/~radev/654w00
Class meets on Fridays, 2:30 - 5:30 PM, 311 WH
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The relational model and
normalization
(cont’d)
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Third normal form (3NF)
• HOUSING (SID, Building, Fee)
• Key: SID
• FD : Building  Fee, SID  Building 
Fee
• Transitive dependencies
• Is HOUSING in 1NF, in 2NF?
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Example
SID Building
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Fee
100
Randolph 1200
150
Ingersoll
200
Randolph 1200
250
Pitkin
300
Randolph 1200
1100
1100
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Third Normal Form (Cont’d)
• Definition: 2NF with all transitive
functional dependencies removed
• Example: STU-HOUSING (SID, Building)
and BLDG-FEE (Building, Fee)
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Boyce-Codd Normal Form
(BCNF)
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ADVISER (SID, Major, Fname)
SID doesn’t determine Major
SID doesn’t determine Fname either
Candidate keys: (SID, Major) or (SID,
Fname)
• Primary key
• Is ADVISER in 1NF? 2NF?
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Example
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SID Major
Fname
100
Math
Cauchy
150
Psychology Jung
200
Math
Riemann
250
Math
Cauchy
300
Psychology Perls
300
Math
Riemann
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BCNF (Cont’d)
• Are modification anomalies possible in
ADVISER?
• BCNF: every determinant must be a
candidate key
• ADVISER: Fname is not a candidate key
• Relations in BCNF have no anomalies as far
as functional dependencies are concerned
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Fourth Normal Form (4NF)
• STUDENT (SID, Major, Activity)
• Key: (SID, Major, Activity)
• Multivalued dependencies:
SID   Major
SID   Activity
• Is the relationship between SID and Major a
functional dependency?
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Update anomalies
SID Major
Activity
100
Music
Swimming
100
Accounting Swimming
100
Music
100
Accounting Tennis
150
Math
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Tennis
Jogging
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4NF (Cont’d)
• Eliminating multi-valued dependencies
• Definition of 4NF: BCNF with no multivalue dependencies
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Domain/Key Normal Form
(DK/NF)
• Fagin (1981) showed that a relation in
DK/NF is one with no modification
anomalies and vice versa
• Definition: every constraint on a relation is
a logical consequence of the definition of
keys and domains
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Constraints in DK/NF
• Any rule governing static values of
attributes that is precise enough so that we
can determine its truth value
• Not included: “Salesperson salary in the
current period can never be less than salary
in the prior period”. Why?
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Keys and domains
• Keys
• Domains: physical description and logical
description
• Definition: a relation is in DK/NF if
enforcing key and domain restrictions
causes all of the constraints to be met
• No formal algorithm
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Example 1
• STUDENT (SID, GradeLevel, Building,
Fee)
• Key: SID
• Constraints: Building  Fee
SID mustn’t start with a 1
• Solution: modify domain of SID
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Example 1 (cont’d)
• Need to make Building  Fee a logical
consequence of a key
• However, building is NOT a key!
– Remove building from STUDENT
– Remove fee from STUDENT
• Every relation should have a single theme!
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DK definition
• Domain Definitions
– SID in CDDD, where C is in {0,2-9} and D is
in {0-9}
– GradeLevel in {FR,SO,JR,SR,GR}
– Building in CHAR(4)
– Fee in DEC(4)
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DK definition (Cont’d)
• Relation and Key Definitions
STUDENT (SID, GradeLevel, Building)
Key: SID
BLDG-FEE (Building, Fee)
Key: Building
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Two more examples
2. PROFESSOR (FID, Fname, Class, SID,
Sname)
3. STU-ADVISER (SID, Sname, FID, Fname,
GradFacultyStatus)
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Foundations of relational
implementation
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Defining relational data
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Relations (tables)
Domains, attributes, constraints
Relational structure (RS)
Occurrence (RS + data)
Relational schemas
Keys: design and implementation semantics
Logical and physical keys
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Implementing a relational
database
• Defining the database structure using a data
definition language (not always needed)
• Allocating media space
• Creating the database data
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Relational data manipulation
• Relational algebra
• Transform-oriented languages
• Query-by-example
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Interfaces to DBMS
• Forms-based data manipulation
• Query/Update language interface:
– SELECT Name, Age
FROM PATIENT
WHERE Physician = ‘Levy’
• Stored procedure interface
– DO BILLING FOR BDATE = ‘9/15/1999’
• Application program interface (API)
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Msql example
$dbh = Msql->connect ($msql_hostname,$msql_databasename)
$sth = $dbh->query (“select title, id from $table_name”)
($title,$id) = $sth->fetchrow();
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Relational algebra
• Relational operators:
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UNION (for union compatible relations)
DIFFERENCE: STUDENT[Name]-JUNIOR[Name]
INTERSECTION
PRODUCT (Cartesian product)
PROJECTION
SELECTION
JOIN: STUDENT JOIN (SID = StudentNumber) ENROLLMENT
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Types of JOIN
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Equijoin
Natural join
Inner join
Outer join (left and right)
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Expressing queries in relational
algebra
• Examples (from book, Chapter 8)
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Readings for next time
• Kroenke
– Chapter 8: Foundations of Relational Implementation
– Chapter 9: Structured Query Language
• YRK (optional)
– Chapter 6: SQL according to MySQL and mSQL
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