5.1 Entities, relationships, and attributes

complex databases are developed in how many phases?1

1. Analysis 2. Logical design 3. Physical design

Analysis steps

1. Discover entities, relationships, and attributes 2. Determine cardinality 3. Distinguish independent and dependent entities 4. Create supertype and subtype entities

An entity-relationship model 3 kinds of objects.

1. entity 2. relationship 3. attribute

Logical desing steps

5. Implement entities 6. implement relationships 7. Implement attributes 8. Normalize tables

What is included in a glossary?

A glossary includes names, synonyms, and descriptions of all entities, relationships, and attributes.

glossary other name?

Data dictionary or repository

Entity Relationship Diagram ofther name?

ER diagram

Attributes (entity-relationship vs. relational models)

In the relational model, attribute is a formal term for column. Since entity-relationship attributes typically become relational columns, the meaning of attribute is similar in both models.

Physical Design

adds indexes and specifies how tables are organized on storage media.

database requirments

are formalized as an entity-relationship model and then implemented in SQL.

Logical design

converts the entity-relationship model into tables, columns, and keys for a particular database system.

Analysis

develops an entity-relationship model, capturing data requirements while ignoring implementation details.

glossary (data dictionary or repository)

documents additional detail in text format. A glossary includes names, synonyms, and descriptions of entities, relationships, and attributes. For simple databases with few users, a database designer may record the glossary with a text editor.

attribute

is a descriptive property of an entity.

entity-relationship model

is a high-level representation of data requirements, ignoring implementation details. An entity-relationship model guides implementation in a particular database system, such as MySQL.

entity

is a person, place, product, concept, or activity.

Entity relationship Diagram (ER diagram)

is a schematic picture of entities, relationships, and attributes. Entities are drawn as rectangles. Relationships are drawn as lines connecting rectangles. Attributes appear as additional text within an entity rectangle, under the entity name.

Entity type

is a set of things. Ex: All employees in a company.

Attribute Type

is a set of values. Ex: All employee salaries.

type

is a set- 1. entity type 2. relationship type 3. attribute type

relationship instance

is a statement about entity instances. Ex: "Maria Rodriguez manages Sales."

relationship type

is a statement about entity types. Ex: Employee-Manages-Department.

relationship

is a statement about two entities.

instance

is an element of a set. 1. entity instance 2. relationship instance 3. atttribute instance

entity instance

is an individual thing. Ex: The employee Sam Snead.

attribute instance

is an individual value. Ex: The salary $35,000.

Entity, relationship, and attribute types usually become?

tables, foreign keys, and columns.

Database design begins with what?

verbal or written requirements for the database