1. Overview of Database Systems
CSCE 315, Fall 2017
Project 1, Lecture 1

2. Project
Your first project (next week) will involve putting together a very basic database system
There will be a few lectures to give you an overview of database systems
This is nowhere close to what you would get in a full database course
Slides adapted from Jennifer Welch (some of hers were from Jeffrey Ullman)

3. Why Database Systems?
Systems designed to manage very large amounts of data, and to query them
Most of these data do not fit in the RAM
Often, key considerations include:
Efficiency,
Safe concurrency
Reliability
Ease of access (querying, distributed)
If an application developer was to implement all these features
He would reinvent the wheel
He may make mistakes
Or he has to relearn couple decades worth of research in a few days
In stead, the developer can just use a database software where all these are already available

4. Creating a Database
A database schema determines what will be represented in the database
This really about which Tables and the structure/schema of those Tables
Specified through a data definition language (DDL)
Once the database is created, then data can be inserted
Like creating a class first and then creating objects of it
Finally, the database can be queried for useful information using Data Manipulation Language (DML)
SQL is used both as DDL and DML

5. Database Design vs Database Development
When we write an application for some other course, most likely we will learn how to organize data in databases
The database software is already there (e.g., MySQL, Microsoft Excel, Oracle, MongoDB)
This is called database design, which means organizing data inside a available database software
However, Team Project #1 is about:
Developing a database engine, since we won’t use the available ones
Then, organizing data inside it for the application part
Therefore, we will learn both database development and data design

6. Database Design
Means setting up the structure inside the database such that:
There is minimal repetition of data
Data access in convenient
Will use Entity-Relationship (ER) model/diagram
Similar to class diagram for Object Oriented Design

7. Entity-Relationship Model
Way of expressing:
Kinds/Types of data and
how they are related
Easy first way to think about databases
Later, relational model described
Relational model is the foundation of most databases

8. Entities and Attributes
Entities are things
Similar to objects in OOP
Correspond to Records
Example: Tanzir is a Person entity
Attributes are properties of entity sets
Correspond to fields in the Records
Example: Tanzir’s birthday, ethnicity
Entity sets are collections of those things
Correspond to Tables
Collection of all A&M employees/personnels

9. Entity Sets and Attributes
Name
Party
Senator
Bill
State
Text
Name
Years

10. Relationships Connect two or more entity sets Name Contributed Party
Organization
Senator
Lobbyist
State
Sponsored
Name
Years
Wrote
Bill
Name
Text

11. Values of Entities and Relationships
The “value” of an entity set is the entities it contains
The “value” of a relationship is a list of currently related entities (one from each entity set)
Senator (Entity Set)
Sponsor (Relationship)
Name
Party
State
Years
Smith
Rep TX 13
Jones
Dem OK 5
Dave CA 12
Senator
Bill
Smith
Tax Bill
Defense Bill
Jones

12. Multi-Way Relationships
E.g. Lobbyist lobbied Senator about Bill
Name
Party
Organization
Senator
Lobbied
Lobbyist
State
Name
Years
Bill
Name
Text

13. Relationship Types
Consider binary relationships (two entity groups in a relationship)
One-to-one
Each entity can have at most one in the other category
e.g. entity groups: Baseball player, Team
relationship: Team MVP
A team can only have one MVP, and a player can only be MVP for one team.

14. Relationship Types
Consider binary relationships (two entity groups in a relationship)
One-to-one
Many-to-one
Each entity of first set can go to at most one of the second set
e.g. entity groups: Person, Town
relationship: BornIn
A person can is born in only one town, but a town can have many people born there

15. Relationship Types
Consider binary relationships (two entity groups in a relationship)
One-to-one
Many-to-one
Many-to-many
Any number from one set to the other
e.g. Senators can sponsor many bills, and each bill can be sponsored by many Senators

16. Diagrams of Relationships
Arrow shows “to one”
Lived In
Born In
Person
Town
MVP
Baseball
Player
Team

17. Attributes on Relationships
Born In
Person
Town
Hospital

18. Keys
A key is a set of attributes for an entity set such that no two entities agree on all the attributes.
We must have a key for every entity set
Name
Party
Senator
State
Years

19. Key for multiple attributes
Must choose one set of attributes
First
Name
Last
Name
Number
Baseball Player
Position
Birthdate
Nationality
Salary
Team

20. Key for multiple attributes
Must choose one set of attributes
First
Name
Last
Name
Number
Baseball Player
Position
Birthdate
Nationality
Salary
Team

21. Key for multiple attributes
Must choose one set of attributes
First
Name
Last
Name
Number
Baseball Player
Position
Birthdate
Nationality
Salary
Team

22. Weak entity sets Need “help” to determine key First Name Last Name
Number
Note arrrow:
indicates many
to one.
Baseball Player
Position
Birthdate
Plays On
Team
Nationality
Salary
Name
City

23. Design Techniques Avoid redundancy Say the same thing two ways First
Name
Last
Name
Number
Baseball Player
Position
Birthdate
Plays On
Team
Team
Name
Salary
Name
City

24. Design Techniques Avoid redundancy Say the same thing two ways First
Name
Last
Name
Number
Baseball Player
Position
Birthdate
Team
Name
Team
Town

25. Design Techniques Don’t use entity set if attribute will do
Entity lists should either
Have some non-key attribute, OR
Be the “many” in a many-one/many-many relationship
Plays On
Name
Baseball Player
Team
Name
City

26. Design Techniques Don’t use entity set if attribute will do
Entity lists should either
Have some non-key attribute
Be the “many” in a many-one/many-many relationship
Name
Baseball Player
Team

27. Design Techniques Don’t overuse weak entity sets
Usually use unique key for each entity set (e.g. UIN, SSN, VIN)
Not always possible, though