Lecture 2: The Process of Database Design

Entity-Relationship model

Enhanced Entity-Relationship model

ER and EER - graphical languages to simplify communication

Mini world

Some part of the real world about which data is stored in a database. EX: tournament

Conceptional Model

A representation of the data structures and relationships in a database without considering how it will be physically implemented.

Key Point: It’s independent of the database technology used later.

DBMS-Independent

Models that work without tying to a specific database system.

Example: Conceptual models.

DBMS-Dependent

Models that require a specific database system for implementation.

Example: Physical design of the database

Attribute(ellipses) круглый

characteristic of an entity in a database that holds data.

Example: For a "Student" entity: "Name”, "Age," or "Student ID."

Domain

The set of valid values for an attribute.

Example: For "Age," the _ could be all positive integers.

1)Atomic vs. Composite

2)Single-Valued vs. Multivalued

3)Stored vs. Derived

4)Null vs. Not Nul

Type of attributes ()

1)Simple values vs. attributes broken into sub-parts (e.g., "Street Number" vs. "Address").

2)Single or multiple values for an entity (e.g., "Car Model" vs. "Car Colors").

3)Directly stored data vs. calculated data (e.g., "Birth Date" vs. "Age").

4)Indicates missing or applicable data.

Entity

A basic object that exists either physically (like a person) or conceptually (like a course).

Entity type

A category of similar entities. Example: All students.

Entity set - rectangular

A collection of entities of the same type. Example: All students currently enrolled in a course.

Key attribute

An attribute that uniquely identifies an entity within an entity set

Relationship - diamond

A connection between two or more entities that describes how they are related to one another. Example: A student enrolls in a course.

Cardinality ratio

1:1

1:Many

Many:Many

Describes how many instances of one entity are related to instances of another entity.

Types

Weak Entity type

An entity type(room) that depends on a related "strong"(building) entity type for identification. Only strong entity type has a primary key.

Participation

Indicates whether the existence of an entity depends on its participation in a relationship: “Does everyone have to join the game?”

Specialization

Group by what makes them different from the main group (Birds, Fish)

Generalization

Group by what they have in common(Birds and Fish are types of animals)

Disjoint VS Overlap

1)Bird cannot be a fish

2)Bird can also be a fish(magical)

Unified Modeling Language

UML

Graphical notation used for database design

• Class: Equivalent to an entity set, divided into three parts: name, attributes, and methods.

• Association: Binary relationships (similar to relationships in ER models).

• Self-Association: A relationship where both ends connect to the same class.

• Association Class: Attributes attached to relationships via a new class.

• Cardinality Constraints: Defines minimum and maximum connections between objects (e.g., "1..N").

Key features of UML

Purpose: Gather information to create a meaningful model.

Approaches: understand and document

1. Document Analysis: Review provided documents.

2. Interviews with End Users: Understand user needs and clarify scenarios.

Modeling steps:

1)Purpose

2)Approaches: (1), (2)