Transcript Unit 1- Database Design power point

Unit 1 – Database
Design
Instructor: Brent Presley
Instructor’s Notes
Database Design Steps
Relational Database Development
Relational Database Development
(See Database Design notes for more details)
(152-156)
Goals: Databases that:
 Adaptable; fields and tables can be added easily
 Flexible; data can be retrieved in unlimited number of ways
 Accurate; no data redundancy, fields limit data entry where possible
1) Fact Finding
a)
b)
Determine fields required for database
Make sure there aren’t multi-part fields
2) Name Tables
a)
Using simple nouns. Use plural or singular for all entity names (don’t mix singular and plural)
3) Draw Entity Relationship diagram
4) Determine Primary Keys for Each Entity

Keys uniquely describe each record of a table
5) Resolve Many-to-Many Relationships
a)
b)
c)
d)
Insert new entity between parents
Name new entity

One instance of parent1 + one instance of parent2 is called what?
Re-evaluate cardinality

Probably 1------M [ ] M--------1
Determine keys for new entity

Probably keys from both parents
6) Determine Foreign Keys (Linking Fields)

For each child entity (many side of a relationship), ensure the key from its parent(s) has been copied to
the child.
7) Remove calculated fields and constants
a)
b)
c)
d)
Make a separate list of calculated fields and equations used to calculate them
Ensure data required to generate calculated fields is available in the field list
Required data can be combined from multiple tables
Constants are fields whose value is the same for all records
8) Name and assign fields (non-key) attributes to appropriate table
a)
b)
Assign to only one table (no redundancy)
Linking fields must be redundant
9) For all fields, determine type and size
a)
b)
c)
Consider specifying value ranges and default values as well
Designate logical keys
Create sample records
10) Ensure no data redundancy except for linking fields.

Watch for synonyms, fields with different (though similar) names
Database Design
Database Design
Notes
Activity
Database Design Goals -- Database that is:
 Adaptable
- Fields and tables can be added (removed) easily
 Flexible
- Data can be retrieved in an unlimited number of ways
 Accurate
- No data redundancy
- Validation on fields
- Default values
- Look ups
Step 1 – Fact Finding
 Determine field (data storage) requirements
 Sources:
- Current users (owners)
- Existing databases
- Existing forms or other documents
 Don’t worry about grouping, simply list
 Split multi-part fields into separate fields
- Example: Split Name into FirstName and
LastName
- Example: Split Address into Street, City, State and
Zip
- Example: Split Phone into AreaCode and Phone,
maybe Extension
Handout Student
Enrollment field list
Step 2 – Name Tables
List tables for Enrollment
Database

Browse through field list, list those tables that are obvious
(others might (will) surface later)
Tools and Resources
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XAMPP (First Part of Quarter)
MySQL Workbench (First Part of Quarter)
Azure (Second Part of Quarter)
Visual Studio Community 2013 (Second Part of Quarter)
SQL (W3Schools)
SQLCourse.com
SQLZoo.net
SQL (TutorialsPoint)
SQL Tutorial
SQL (TutsPlus)
Essential SQL
Learn SQL The Hard Way
Udemy Training (Free): Sachin Quickly Learns SQL
Udemy Training (Free): Database Design
Udemy Training (Free): MySQL Database for Beginners
Udemy Training (Free): SQL Server for Beginners
3
WHAT IS A DATABASE?
• What is a database?
– https://www.youtube.com/watch?v=t8jgX1f8kc4
• Introduction to Databases
– This will preview a lot of information that we will
discuss in more detail in the weeks to come
– https://www.youtube.com/watch?v=4Z9KEBexzc
M
HISTORY OF DATABASE
SYSTEMS
• File systems (before mid 1960s)
Problems: Data redundancy
update anomalies
no abstract data model
requires knowledge of storage
details
no standard query language
HIERARCHICAL DATABASES
(MID 1960S)
Developed by North American Rockwell and IBM
as the IMS (Information Management System)
Based on a tree structure
Example: A Product assembled from components,
which are assembled from subcomponents
Problems: Changes in data structure require changes
in application programs that access that structure
No Many-to-Many relationships
Programmers must be thoroughly familiar with the
database structure.
NETWORK DATABASES
• Extension of the hierarchical data model
• Standardized (1971) by the CODASYL
group (Conference on Data Systems
Languages)
Advantage: Many-to-Many relationships are
implemented
Problems: “Navigation” is even harder
RELATIONAL DATABASES
Proposed in 1970 by E.F. Codd while working at
IBM.
“IBM largely ignored his work, as the company
was investing heavily at the time in
commercializing IMS databases….
It was not until 1978 that Frank T. Cary, then
chairman and CEO of IBM ordered the
company to build a product based on Dr.
Codd’s ideas.
Oracle emerges
But IBM was beaten to the market by Lawrence J. Ellison, a Silicon
Valley entrepreneur, who used Dr. Codd’s papers as the basis of a
product around which he built a start-up company that has since become
the Oracle Corporation.”
New York Times April 23, 2003
Obituary of E. F. Codd (1923-2003)
1. RELATIONAL DATABASES
Data Abstraction- allows people to forget
unimportant details
View Level – a way of presenting data to a
group of users
Logical Level – how data is understood to be
when writing queries
WHAT IS A NULL?
• It basically means both since the a
column allows NULL and there is no default
value set for the column. If you insert into the
table and don't specify a value and there is
no default value for the column, the value
will be null (undefined).
ENTITY
• An entity can be a real-world object, either animate or inanimate, that
can be easily identifiable. For example, in a school database, students,
teachers, classes, and courses offered can be considered as entities.
All these entities have some attributes or properties that give them their
identity.
• An entity set is a collection of similar types of entities. An entity set may
contain entities with attribute sharing similar values. For example, a
Students set may contain all the students of a school; likewise a
Teachers set may contain all the teachers of a school from all faculties.
Entity sets need not be disjoint.
ATTRIBUTES
• Entities are represented by means of their properties, called
attributes. All attributes have values. For example, a
student entity may have name, class, and age as attributes.
• There exists a domain or range of values that can be
assigned to attributes. For example, a student's name
cannot be a numeric value. It has to be alphabetic. A
student's age cannot be negative, etc.
ATTRIBUTE TYPES
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Simple attribute − Simple attributes are atomic values, which cannot be
divided further. For example, a student's phone number is an atomic value of 10
digits.
Composite attribute − Composite attributes are made of more than one simple
attribute. For example, a student's complete name may have first_name and
last_name.
Derived attribute − Derived attributes are the attributes that do not exist in the
physical database, but their values are derived from other attributes present in
the database. For example, average_salary in a department should not be
saved directly in the database, instead it can be derived. For another example,
age can be derived from data_of_birth.
Single-value attribute − Single-value attributes contain single value. For
example − Social_Security_Number.
Multi-value attribute − Multi-value attributes may contain more than one
values. For example, a person can have more than one phone number,
email_address, etc.
KEYS
• Key is an attribute or collection of attributes that uniquely
identifies an entity among entity set.
• For example, the roll_number of a student makes him/her
identifiable among students.
• Super Key − A set of attributes (one or more) that
collectively identifies an entity in an entity set.
• Candidate Key − A minimal super key is called a candidate
key. An entity set may have more than one candidate key.
• Primary Key − A primary key is one of the candidate keys
chosen by the database designer to uniquely identify the
entity set.
RELATIONSHIPS
• The association among entities is called a
relationship. For example, an employee
works_at a department, a student enrolls in
a course.
RELATIONSHIP SET
• A set of relationships of similar type is called a relationship
set. Like entities, a relationship too can have attributes.
These attributes are called descriptive attributes.
• Degree of Relationship
• The number of participating entities in a relationship defines
the degree of the relationship.
• Binary = degree 2
• Ternary = degree 3
• n-ary = degree
Cardinality
• One-to-one − One entity
from entity set A can be
associated with at most
one entity of entity set B
and vice versa.
Cardinality
• One-to-many − One
entity from entity set A
can be associated with
more than one entities of
entity set B however an
entity from entity set B,
can be associated with at
most one entity
Cardinality
• Many-to-one − More
than one entities from
entity set A can be
associated with at most
one entity of entity set B,
however an entity from
entity set B can be
associated with more
than one entity from entity
set A.
Cardinality
• Many-to-many − One
entity from A can be
associated with more
than one entity from B
and vice versa.
DATABASE DESIGN GOALS
– Adaptable
• Fields and tables can be added (removed) easily
– Flexible
• Data can be retrieved in an unlimited number of ways
– Accurate
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No data redundancy
Validation on fields
Default values
Look ups
SMALL GROUP PROJECT
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You are a known database developer and the parent of a thirteen-year-old son who is
actively involved in the local Junior League Baseball program. Your son will be playing in
one of the 12 local teams who will be competing in the National Division Junior League
Tournament. Each pair of local teams plays twice against each other during the fourmonth season. With the intention of creating the best conceivable national team, the U.S.
Junior Baseball League president, Mr. Henry Zemog, wants to gather appropriate
statistics from all team players during the National Division Junior League Tournament.
You have been asked by Mr. Zemog to design a database for tracking each team’s and
player’s statistics during the tournament series. The national team will represent the
United States in the International Junior League World Series Tournament to be held in
Heritage Park in Taylor, Michigan. You will have access to the complete game statistics
for each game that is played. You have agreed to fulfill this task.
Using the lessons learned in Chapter 1 about the relational model and your knowledge of
basic baseball statistics, use your favorite drawing tool to produce a relational diagram
that can serve as a preliminary step toward the final database design. At this stage of the
development process, the basic constructs should include only the entities and their
relationships. Name the diagram “Junior League Baseball Database.”
POTENTIAL ANSWER TO GROUP
PROJECT
• There are many possible solutions…
GROUP PROJECT 2
• You are in the requirements analysis phase
of designing a database for an organization.
• List the pieces of information that you need
to acquire from stakeholders in order to
• minimize shortcomings and iterations during
the preliminary design phase.
POTENTIAL ITEMS FOR GROUP PROJECT
2
A list of products and services the organization provides
• An organizational chart, a list of stakeholders, and a list of job
responsibilities
• Current handling of the information system and record keeping
• Current storage of the data and information, such as forms and reports
• Department that will take ownership of the system
• Personnel responsible for using, entering, and maintaining the data
• Security levels
• Location of the database
• Infrastructure, software, and hardware equipment
ENHANCED BASEBALL TABLE
• Add offensive and defensive statistics to the
earlier example
DATA NORMALIZATION
• Database Normalization is a technique of organizing the
data in the database. Normalization is a systematic
approach of decomposing tables to eliminate data
redundancy and undesirable characteristics like Insertion,
Update and Deletion Anamolies. It is a multi-step process
that puts data into tabular form by removing duplicated data
from the relation tables.
• Normalization is used for mainly two purpose,
• Eliminating reduntant(useless) data.
• Ensuring data dependencies make sense i.e data is
logically stored.
ASSIGNMENT IN GROUPS OF 2-3
• Use the Internet to research normal forms
and explain any drawbacks to normalizing
data. In your own words, write a one-page
summary of your findings and any additional
recommendations or observations that you
may have.
• Include title and reference page (not to be
counted toward total pages).
STEPS IN BUILDING A DATABASE
STEP 1- FACT FINDING
•Determine field (data storage) requirements
•Sources:
Current users (owners)
Existing databases
Existing forms or other documents
•Don’t worry about grouping, simply list
•Split multi-part fields into separate fields
Example: Split Name into FirstName and LastName
Example: Split Address into Street, City, State and Zip
Example: Split Phone into AreaCode and Phone, maybe Extension
Handout Student Database field list
Assign Terminology Worksheet
Student enrollment db fields
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Social Security Number
Student Name
Email
Program Code
Program Name
GPA
Phone number
Phone type
Street Address
City
State
Zip Code
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Instructor Number
Instructor Name
Instructor Home Phone
Instructor Business Phone
Email Address
Web Site
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Course Grade
Course Number
Course Name
Description
Credits
Course Time
Course Days
Instructor Number
STEP 2 – NAME TABLES
• Browse through field
list, list those tables
that are obvious
(others might (will)
surface later)
•
List tables for
Enrollment Database
•Table Naming Conventions
Add the tbl prefix to each table name
Name tables using either plural nouns or
singular nouns. Don’t mix with in a database.
-E.g. tblCustomers, tblLocations,
tblVehicles
-E.g. tblCustomer, tblLocation, tblVehicle
-Unique and descriptive
-2012: Lean towards plural nouns
Ensure abbreviations are clear to everyone, not
just those involved in the project.
Brief, but complete
-Use minimum words necessary
Don’t include database terminology: Record,
File, Table
Don’t include adjectives that restrict data
-Example: Wisconsin Rapids Employees,
Stevens Point Employees
Results in duplicate structures. Structures (field lists)
of both tables will be identical
STEP 2- NAME TABLES
– Make a separate table for multi-value fields.
• Example: a field named Hobbies might contain
“bowling, fishing”
• Create a separate Hobbies entity (each hobby will be
listed as a separate record in this table)
• Multi-value fields are difficult to search and nearly
impossible to validate or sort.
• Tip: if the field name is plural, it’s probably a
multi-value field.
STEP 3- DRAW ENTITY RELATIONSHIP
DIAGRAM
• Entity Relationship Diagram (ERD) is picture that shows the
relationships between tables of a database
• Helps discover additional tables and defines relationships
• Rectangle used to represent each table in a database
• Line drawn between tables that are directly related
• At end of each line, include cardinality
– One occurrence in table 1 is related to how many occurrences of
table 2 (maximum number)
– One occurrence in table 2 is related to how many occurrences of
table 1 (maximum number)
– For our purposes, the maximum is listed as 1 or many (M)
ENTITY RELATIONSHIP DIAGRAM
– The above ERD fragment expresses that:
• “One lab contains (M)any computers”
• “One computer exists in only one (1) lab”
• Entity Relationship Diagram (ERD)
• https://www.youtube.com/watch?v=-fQ-bRllhXc
FOR MORE INFORMATION
• Data modelling and the ER model
– https://www.youtube.com/watch?v=IfaqkiHpIjo
(60)
ERD CONCEPTS
• Crows feet
notationdesignates the
cardinality of the
relationship
ERD CONCEPTS
DRAW THE ERD FOR THIS (GROUP)
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As a part of its project management database, the company wants to store
information about resources (employees), projects and bookings.
For each employee, the following information is stored: Employee ID, First and
Last name, Rank, and billing rate. Employees are organized into solution sets,
each solution set has a head of the solution set, who is the resource owner for
all employees in that SS. For each solution set we record the SS ID and the SS
name. For scheduling purposes, we want to store information about the head
of each solution set, and about assignment of employees to solution sets. An
employee can belong to only one solution set.
The scheduling system also stores information about project. For each project,
the following information is stored: Project ID, Status, Location and Client name.
As a part of the scheduling system, we store information about each calendar
day in a year. When a booking is requested for an employee, the employee is
scheduled to work on a particular project, on a particular day for the specified
amount of time (10%-100%). For each booking we also record current status
SOLUTION
DRAW THE ERD FOR THIS (GROUP)
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On-line payment system stores information about all customers, including
name, id, address, e-mail and password. Each customer has set up a specific
method of payment, which may be a credit card payment or automated direct
withdrawal. For all types of payment we store the following information: an ID
and the date the method of payment was set up. For credit card payments we
store CC number and type and the expiration date. For automated withdrawal
we store the name of financial institution, the routing number, account number
and the date of monthly withdrawal.
SOLUTION
STEP 4 – DETERMINE PRIMARY KEY
• – Determine Primary Key for each Entity
– The primary key is the field or fields whose value
uniquely identifies a record in that table.
• For Lab, it might be Room Number
• For Computer, it might be ID Number
STEP 4 – DETERMINE PRIMARY KEY
• Primary keys can be a combination of two
keys
• For Lab, if the building has multiple floors, a
combination key might be Room Number plus Floor
(e.g. Room 10 on Floor 5)
STEP 4 – DETERMINE PRIMARY KEY
– If you need to combine 3 or more fields to create
a unique primary key, consider creating an ID
Number field for that table (surrogate key).
• These keys are usually autonumber fields
• Often times these are used in all tables.
– Primary key requirements:
• Unique. No two keys will have the same value
• Cannot be null. In multi-field keys, none can be null
• Values in field rarely (if ever) change
PRIMARY KEY CONSIDERATIONS
• Primary keys should be as small as necessary. Prefer a numeric type
because numeric types are stored in a much more compact format than
character formats. This is because most primary keys will be foreign
keys in another table as well as used in multiple indexes. The smaller
your key, the smaller the index, the less pages in the cache you will
use.
• Primary keys should never change. Updating a primary key should
always be out of the question. This is because it is most likely to be
used in multiple indexes and used as a foreign key. Updating a single
primary key could cause of ripple effect of changes.
• Do NOT use "your problem primary key" as your logic model primary
key. For example passport number, social security number, or
employee contract number as these "primary key" can change for real
world situations.
•
http://stackoverflow.com/questions/337503/whats-the-best-practice-for-primary-keys-in-tables
SURROGATE VS NATURAL KEY
• On surrogate vs natural key, I refer to the
rules above. If the natural key is small and
will never change it can be used as a
primary key. If the natural key is large or
likely to change I use surrogate keys. If there
is no primary key I still make a surrogate key
because experience shows you will always
add tables to your schema and wish you'd
put a primary key in place
EXAMPLE
• Define keys for enrollment database
STEP 5 – RESOLVE MANY TO MANY
RELATIONSHIPS
– Many-to-Many (M-M) are relationships where
the cardinality is M (many) in both directions.
• The Lab-Computer example above is a 1-M (one-tomany) relationship. The following represents a M-M
relationship
• “One customer orders many products.”
• “One product is purchased by many customers.”
MANY TO MANY RELATIONSHIPS
– M-M relationships are nearly impossible to
implement using a database program
– M-M relationships must be resolved into multiple
1-M relationships in order to implement the
database
RESOLVING M-M RELATIONSHIPS
• Insert a new entity between the two entities
• Name the new entity.
– ”What is one occurrence of table1 combined with one
occurrence or table2 called?”
– ”One customer ordering one product is called…?
an ordered product.”
• Re-evaluate the cardinality of the new relationships
• Probably 1----M [] M----1
(Manys attached to new entity)
M-M RELATIONSHIPS
• Determine the primary keys (always at least 2) for the new entity.
• Usually the keys from the two parents
Parent entities are those on the 1 side of a relationship (Customer and
Product)
Child entities are those on the M side of a relationship (Ordered
Product)
One entity can be the parent in one relationship and a child in a
different relationship.
OTHER RELATIONSHIP ISSUES
• What happens to child records when parent
records are deleted?
– Restrict Delete
• Parent record cannot be deleted until all child records (in all child
tables) have been deleted.
• Preferred technique. Requires consideration of affects of
deleting this parent record
– Cascade delete
• When a parent record is deleted, all associated child records (in
all child tables) are automatically deleted
• dangerous
STEP 6 – DETERMINE FOREIGN KEYS
• For every relationship, the primary key from the parent table
must exist in the child table. This is what links the tables
together in a relational database.
• Often, the links will already exist because of M-M
resolution.
• If the parent’s primary key does not exist in the child, copy
the field into the child table.
– This field DOES NOT become part of the child’s primary key.
– Designate the field as a link (L) – for data dictionary
Copy keys from Student, Section, and
Instructor into child tables.
STEP 7 – REMOVE CALCULATED FIELDS AND
CONSTANTS
• Because today’s computers are so fast, it’s better
to calculate these values as you need them instead
of storing them in the database.
• Additionally, if you calculate them as you need
them, you ensure the values are always up to date.
• Make a separate list of the calculated fields you
removed. Include the equation used to calculate
the value.
STEP 7 – REMOVE CALCULATED FIELDS AND
CONSTANTS
– Ensure all the parts of the equations are stored
somewhere in the database.
• Equation parts can be stored in different tables
(linking allows you to bring them together)
– If parts can be calculated, don’t store them
either
STEP 7 – REMOVE CALCULATED FIELDS AND
CONSTANTS
– Constants are fields that ALWAYS store the
same value
• No need to waste storage space
• Print the constant value on reports when needed
• There are exceptions to this rule. Values that
rarely change, though calculated, may be
fields in the database. I’ve never run into an
instance of this though
UPDATE DATABASE
Remove GPA from Student table
GPA = Total Points /
Total Credits
Total Points = Sum of all grade points
Total Credits = Sum of all credits earned
Grade Points available (determined from letter grade)
•Credits Earned available
Remove State (constant)
Remove City, create ZipCity table to lookup city based on zip
Zip is linking field in Student
Assign fields to entities in Enrollment database
STEP 8- ASSIGN REMAINING FIELDS TO
ENTITIES
– For all remaining fields (from Step 1), assign to
one and only one table.
• Only linking fields may be duplicated in a
database
FIELD NAMING STANDARDS
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Field Naming Standards
– Apply to primary keys and linking fields as well.
– Use singular nouns
• If plural makes more sense, this is not a field but another table.
– Unique and descriptive
• Include table name when field name occurs in two tables (StudentAddress,
InstructorAddress)
(optional)
– Use minimum number of words
– Use acronyms and abbreviations wisely (only if everyone understands them)
– If the name includes “/” “&” “-“ “and” “or”, it probably represents two or more fields.
Split them.
– Split multipart fields into separate fields
• If a field can be decomposed into parts, it’s probably more than one field.
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Example: Address (street, city, state, zip)
Phone (area code, number, extension)
STEP 9 – FOR ALL FIELDS, DETERMINE
TYPE AND SIZE
– Use types and sizes available in your database program
– Types and sizes of linking fields (foreign keys) must
be identical in each table
– MYSQL : int or varchar
• Varchar(20)
• Int (if it’s automatically assigned)
MYSQL COMMON DATA TYPES
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VARCHAR (string 0-255 characters)
TEXT (0-65k characters)
INT
BIGINT
DATE
DATETIME
BOOLEAN
• http://www.cheatography.com/davechild/che
at-sheets/mysql/
MYSQL DATA TYPES
• Complete listing
STEP 10 – ENSURE NO REDUNDANCY
EXCEPT LINKING FIELDS
– Check for synonyms, two fields with different
names that are actually the same thing.
• Example: Social Security Number and Employee ID
• Double-check to ensure non-linking fields
only occur in one entity
STEP 10 – ENSURE NO REDUNDANCY
EXCEPT LINKING FIELDS
• Field Formatting / Validation Considerations
– Designate digits required for text field
– Use a lookup for this field
– All linking fields should be lookups
– Autocap: automatically capitalize the first letter
of each word in the field
– Uppercase: automatically capitalize all letters in
the field
– N1-n2: numeric value range check
STEP 10 – ENSURE NO REDUNDANCY
EXCEPT LINKING FIELDS
• Field Formatting / Validation Considerations
– Auto populate from field
• Automatically populate this field from another field in
the database (credits earned = current credits)
• Not a lookup
• User not usually allowed to edit
– Required
• Keys are automatically required
ADDITIONAL THOUGHTS
– Database design is best done by a group of people unless you have
significant experience.
– Don’t be afraid of undiscovered errors in your design
• When you build the database, errors will surface and you can correct
them early
• When you populate the tables with data, other errors might surface.
Again, you’ll usually catch these early on.
• If you follow these guidelines, your database will be
adaptable, flexible and accurate. Any design errors you
find after using the database for a while (lots of data
entered) should still be relatively easy to correct, especially
with Access’ help
DATA DICTIONARY
• •A data dictionary, or data repository, is a
central storehouse of information about the
system’s data
• •An analyst uses the data dictionary to collect,
document, and organize specific facts about the
system
• •Also defines and describes all data elements and
meaningful combinations of data elements
DATA DICTIONARY
 Documenting the Data Elements
• ◦You must document every data
element in the data dictionary
• ◦The objective is the same: to
provide clear, comprehensive
information about the data and
processes that make up the system
DATA DICTIONARIES
Data dictionary must contain the following information:
• Table Name
• Field (attribute) name
• Expanded field name
• Field contents or long description
• Data type and length or size
• Default value(s)
• Format (required or optional digits or characters & sequence of
characters if appropriate)
• Domain (range or choices)
• Allow NULL? (Y or N)
• Key (PK or FK)
• Foreign Key referenced table
DATA DICTIONARY DOCUMENT
DATA DICTIONARY DOCUMENT