Intro-ish Flashcards
What are the levels of Database Architecture?
- External - what the user sees,
- Internal - how the computer physically stores the database,
- Conceptual - the logic of the database’s operation.
What are the importances of data modelling?
- It helps with efficient computerisation,
- It represents the real world.
What is the ER model?
The Entity Relationship model is a blueprint for designing databases.
What are the main concepts of an ERM?
- Entities,
- Relationships,
- Attributes (characteristics of entities),
- Cardinality
What are the properties of ERD?
- Entities are represented with rectangles,
- Characteristics are represented by ovals,
- Relationships by diamonds,
- Cardinalities by their respective numbers.
What is an entity in an ERD?
It is a noun; it is the basic or conceptual element of an ERD that exists on its own.
What is a relation?
A relation is the association between two or more entities.
What is the Enhanced Entity Relationship Model?
The EER model is a data model with more extensions to the ER model, including superclasses, subclasses, specialisation and generalisation.
What are superclasses?
Groups of entities which share common attributes.
What is a superclass (supertype)?
A group of entities that share common attributes.
What is a subclass (subtype)?
Subsets of an entity (superclass) from which it inherits attributes.
What is specialisation?
The act of breaking down an entity into smaller entities which share common attributes.
What is generalisation?
Process of pooling different but related entities into a single entity (superclass).
Who is a database administrator?
One who designs and manages a database.
They are responsible for administrative parts as well as acquiring hardware and software required to maintain database.
Who are application designers and programmers?
They create and maintain the program that accesses the database.
Who are the end users?
The people who access the database for the information it holds.
In converting from a conceptual (analysis) to a physical (implementation) model, what are the key notes or transformations?
- Entities become tables
- Attributes become columns
- Primary unique identifiers become primary keys
- Secondary unique identifiers become unique keys
- Instances become rows
What are the types of database languages?
- Data Definition Language (DDL): used to create schema or structure of the database.
- Data Manipulation Language (DML): used to manipulate (add, delete, insert) instances (data) in the database.
- Data Control Language (DCL): is used to manage who has access to the database.
What is schema?
Structure or design of the database.
What are instances?
Data itself stored in the database.
