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
