Database Fundamentals 2 Flashcards
What is a model?
An abstraction of a real-world object or event.
It is useful in understanding the complexities of the real world environment.
What is a data model?
Relatively simple representation of complex real-world data structure.
It is often graphical.
It is an abstraction - One cannot draw the required data out of the data model.
Data Model Basic Building Blocks (4)
- Entity: anything about which data are to be collected and stored.
- Attribute: A characteristic of an entity.
- Relationship: Describes an association among entities.
- One to many (1:M)
- Many to many (M:M)
- One to one (1:1) - Constraint: A restriction placed on the data
What are Business Rules?
Description of policies, procedures or principles within a specific organization.
Translating business rules into data model components
- Generally, nouns translate into entities.
- Verbs translate into relationships among entities.
- Relationships are bidirectional.
Two questions to identify the relationship type
- How many instances of B are related to one instance of A?
2. How many instances of A are related to one instance of B?
What is the Entity Relationship Model?
It is the widely accepted standard for data modeling.
It is a graphical representation of entities and their relationships in a database structure.
Entity set
Collection of like entities that are usually mapped to a relational table.
Entity instance
A row in a table
Entity attribute
A column in a table
What is connectivity?
It describes the relationship classification/type
What is cardinality?
Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity.