(C) 2000, The University of Michigan 1 Database Application Design Handout #4 January 28, 2000

(C) 2000, The University of Michigan 2 Course information Instructor: Dragomir R. Radev Office: 305A, West Hall Phone: (734) Office hours: Thursdays 3-4 and Fridays 1-2 Course page: Class meets on Fridays, 2:30 - 5:30 PM, 311 WH

(C) 2000, The University of Michigan 3 The relational model and normalization (cont’d)

(C) 2000, The University of Michigan 4 Third normal form (3NF) HOUSING (SID, Building, Fee) Key: SID FD : Building  Fee, SID  Building  Fee Transitive dependencies Is HOUSING in 1NF, in 2NF?

(C) 2000, The University of Michigan 5 Example

(C) 2000, The University of Michigan 6 Third Normal Form (Cont’d) Definition: 2NF with all transitive functional dependencies removed Example: STU-HOUSING (SID, Building) and BLDG-FEE (Building, Fee)

(C) 2000, The University of Michigan 7 Boyce-Codd Normal Form (BCNF) 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?

(C) 2000, The University of Michigan 8 Example

(C) 2000, The University of Michigan 9 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

(C) 2000, The University of Michigan 10 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?

(C) 2000, The University of Michigan 11 Update anomalies

(C) 2000, The University of Michigan 12 4NF (Cont’d) Eliminating multi-valued dependencies Definition of 4NF: BCNF with no multi- value dependencies

(C) 2000, The University of Michigan 13 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

(C) 2000, The University of Michigan 14 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?

(C) 2000, The University of Michigan 15 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

(C) 2000, The University of Michigan 16 Example 1 STUDENT (SID, GradeLevel, Building, Fee) Key: SID Constraints: Building  Fee SID mustn’t start with a 1 Solution: modify domain of SID

(C) 2000, The University of Michigan 17 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!

(C) 2000, The University of Michigan 18 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)

(C) 2000, The University of Michigan 19 DK definition (Cont’d) Relation and Key Definitions STUDENT (SID, GradeLevel, Building) Key: SID BLDG-FEE (Building, Fee) Key: Building

(C) 2000, The University of Michigan 20 Two more examples 2. PROFESSOR (FID, Fname, Class, SID, Sname) 3. STU-ADVISER (SID, Sname, FID, Fname, GradFacultyStatus)

(C) 2000, The University of Michigan 21 Foundations of relational implementation

(C) 2000, The University of Michigan 22 Defining relational data Relations (tables) Domains, attributes, constraints Relational structure (RS) Occurrence (RS + data) Relational schemas Keys: design and implementation semantics Logical and physical keys

(C) 2000, The University of Michigan 23 Implementing a relational database Defining the database structure using a data definition language (not always needed) Allocating media space Creating the database data

(C) 2000, The University of Michigan 24 Relational data manipulation Relational algebra Transform-oriented languages Query-by-example

(C) 2000, The University of Michigan 25 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)

(C) 2000, The University of Michigan 26 Msql example $dbh = Msql->connect ($msql_hostname,$msql_databasename) $sth = $dbh->query (“select title, id from $table_name”) ($title,$id) = $sth->fetchrow();

(C) 2000, The University of Michigan 27 Relational algebra Relational operators: –UNION (for union compatible relations) –DIFFERENCE: STUDENT[Name]-JUNIOR[Name] –INTERSECTION –PRODUCT (Cartesian product) –PROJECTION –SELECTION –JOIN: STUDENT JOIN (SID = StudentNumber) ENROLLMENT

(C) 2000, The University of Michigan 28 Types of JOIN Equijoin Natural join Inner join Outer join (left and right)

(C) 2000, The University of Michigan 29 Expressing queries in relational algebra Examples (from book, Chapter 8)

(C) 2000, The University of Michigan 30 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