Databases Flashcards
What are the disadvantages of a file-based system?
- Separation of data
- Duplication of data
- Data dependence - difficult to change structure
- Incompatible file formats
- Fixed queries - difficult to do ad hoc queries
- Low reliably, security, & integrity
What is the definition of a Database Management System (DBMS)?
A software system that allows users to define, create, and maintain a controlled-access database
What are the two languages a DBMS provides?
Data Definition Language (DDL)
Data Manipulation Language (DML)
What are the advantages of a database?
- Consistent & structured model of data
- Efficient filing
- Ad hoc queries
- Easy to update
- Concurrency
- Greater security
What is an entity?
Objects or things from the real world (People or places…)
What is an attribute?
A property of an entity (things that describe the entity)
A set of entities of the same type is represented as what?
A table, or relation.
What does each row in a table represent?
The entities
What does each column in a table represent?
The attributes
What is an atomic place in a table called?
A cell
What is a superkey?
A set of one or more attributes that uniquely identify an entity within a table
What is a candidate key?
Any attribute that can quality as a primary key
What is a primary key?
The attribute selected to uniquely identify the entity
What is a relation schema?
A set of attribute names and their domains
What is a foreign key?
An attribute that references an attribute, usually the PK, of another table, ensuring integrity.
