1 A Guide to MySQL 2 Database Design Fundamentals

Objectives A Guide to MySQL 2  Understand the terms entity, attribute, and relationship  Understand the terms relation and relational database  Understand functional dependence and be able to identify when one column is functionally dependent on another  Understand the term primary key and identify primary keys in tables

Objectives (continued) A Guide to MySQL 3  Design a database to satisfy a set of requirements  Convert an unnormalized relation to first normal form  Convert tables from first normal form to second normal form  Convert tables from second normal form to third normal form  Create an entity-relationship diagram to represent the design of a database

Introduction A Guide to MySQL 4  Database design: process of determining the particular tables and columns that will comprise a database  Must understand database concepts  Process of normalization  Don’t be afraid to make mistakes as long as you are willing to make changes.

Relational Database A Guide to MySQL 5  A collection of tables  A relational database is a collection of data items organized as a set of formally-described tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables.  The relational database was invented by E. F. Codd at IBM in 1970.

A Guide to MySQL 6 Relational Database (continued)

A Guide to MySQL 7

8

Entities, Attributes, and Relationships A Guide to MySQL 9  Entity (like a noun): person, place, thing or event  Attribute (like an adjective or adverb): property of an entity  Describes the entity ex. Fiction may be an attribute of Book  Belongs to the entity ex. Address may be associated with a Person  Relationship: association between entities

Entities, Attributes, and Relationships (continued) A Guide to MySQL 10  Cardinality: numeric relationships between occurrences of the entities on either end of a relationship line  One-to-one  One-to-many One rep is related to many customers; but customers have a single rep Implement by having a common column in two or more tables  Many-to-many

Entities, Attributes, and Relationships (continued) A Guide to MySQL 11  Repeating groups: multiple entries in an individual location (multiple entries in the same column of a single row)  Repeating groups merely take up space and resources and  Repeating groups add no additional information

A Guide to MySQL 12

A Guide to MySQL 13

Entities, Attributes, and Relationships (continued) A Guide to MySQL 14  A relation is a two-dimensional table:  Entries in the table are single-valued  Each column has a distinct name  All values in a column are values of the same attribute  The order of the columns is immaterial  Each row is distinct  The order of the rows is immaterial

Entities, Attributes, and Relationships (continued) A Guide to MySQL 15  Use shorthand representation to show tables and columns REP (REP_NUM, LAST_NAME, FIRST_NAME, STREET, CITY, STATE, ZIP, COMMISSION, RATE) CUSTOMER (CUSTOMER_NUM, CUSTOMER_NAME, STREET, CITY, STATE, ZIP, BALANCE, CREDIT_LIMIT, REP_NUM) ORDERS (ORDER_NUM, ORDER_DATE, CUSTOMER_NUM) ORDER_LINE (ORDER_NUM, PART_NUM, NUM_ORDERED, QUOTED_PRICE) PART (PART_NUM, DESCRIPTION, ON_HAND, CLASS, WAREHOUSE, PRICE)

Entities, Attributes, and Relationships (continued) A Guide to MySQL 16  Qualify a name: refers to the process of qualifying a name by concatenating the name of the table with the name of the attribute  It is always acceptable to qualify column names (attributes), even if there is no potential for confusion.  Example: a museum has a database with tables: customer, friends, and employees. How can confusion arise if attributes are not qualified in a discussion of this database?

Functional Dependence A Guide to MySQL 17  An attribute, B, is functionally dependent on another attribute (or collection), A, if a value for A determines a single value for B at any one time  Functional dependencies cannot determine from sample data; must know the users’ policies  Example: Compare a retail salesperson’s relationship to a customer with a drug representative visiting a doctor. In either case, explain how the relationship can be one-to-many or many-to-many.  Why are the business rules needed to answer this question?

A Guide to MySQL 18 Functional Dependence

Primary Keys A Guide to MySQL 19  Unique identifier for a table  Column (attribute) A (or a collection of columns) is the for a table (relation) R if:  Property 1: all columns in R are functionally dependent on A  Property 2: no subcollection of the columns in A (assuming that A is a collection of columns and not just a single column) also has Property 1

Database Design A Guide to MySQL 20  Design a database given a set of requirements that database must support  Requirements gathered through a process known as systems analysis  In many cases problems are not obvious at the early design steps  Have someone play devil’s advocate  Try to mentally “run” the data

Design Method A Guide to MySQL 21 Read requirements, identify entities (objects) involved, and name the entities. Identify unique identifiers for entities identified above Identify the attributes for all entities Identify functional dependencies that exist among attributes Use functional dependencies to identify tables by placing each attribute with attribute or minimum combination of attributes on which it is functionally dependent Identify any relationships between tables

Database Design Requirements A Guide to MySQL 22  For Premiere Products:  Store data about sales reps, customers, parts, orders, and order line items  Must enforce certain constraints; for example: There is only customer per order Quoted price may differ from actual price

Normalization A Guide to MySQL 23  Identify the existence of potential problems  Provides a method for correcting problems  Goal: convert unnormalized relations (tables that contain repeating groups) into various types of normal forms  Is complete normalization necessary in all cases?  Why or why not?  What is the bottom line for design?

Normalization (continued) A Guide to MySQL 24  First normal form (1 NF): better than unnormalized  Second normal form (2 NF): better than 1 NF  Third normal form (3 NF): better than 2 NF

First Normal Form (1NF) A Guide to MySQL 25  A relation is in first normal form (1NF) if it does not contain any repeating groups (multiple entries in a single row)  To convert an unnormalized relation to 1NF: expand PK to include PK of repeating group (effectively eliminating the repeating group from the relation)  Does first normal form indicate anything about cardinality? (Look at the next two slides and come back to this question)

A Guide to MySQL 26

A Guide to MySQL 27

Second Normal Form A Guide to MySQL 28  Redundancy causes problems  Example a part with multiple descriptions pg. 46/7  Update anomalies  Update - If one description is changed; it doesn’t change the other description.  Inconsistent data - Part descriptions now disagree.  Additions – What description will be applied to a new part?  Deletions – instantiation vs. storage

Second Normal Form (continued) A Guide to MySQL 29  A relation is in second normal form (2NF) if it is in 1NF and no nonkey attribute is dependent on only a portion of the primary key  Or: all nonkey attributes are functionally dependent on entire primary key  If the primary key is a single column of a table in 1NF, then the table is automatically in 2NF.

A Guide to MySQL 30

Third Normal Form A Guide to MySQL 31  Update anomalies still possible  Determinant: an attribute (or collection) that functionally determines another attribute  A relation is in third normal form (3NF) if it is in 2NF and the only determinants it contains are candidate keys  Boyce-Codd normal form (BCNF) is the true name for this version of 3NF

A Guide to MySQL 32

Diagrams for Database Design A Guide to MySQL 33  Graphical illustration  Entity-relationship (E-R) diagram:  Rectangles represent entities  Arrows represent relationships

A Guide to MySQL 34 Diagrams for Database Design (continued)

A Guide to MySQL 35 Diagrams for Database Design (continued)

A Guide to MySQL 36 Diagrams for Database Design (continued)