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.
What is meant by relational integrity?
A set of rules that ensure that the data is accurate
What is the first normal form?
Whether the fields are atomic, or as compressed as they can be
What is second normal form?
Must be 1NF & each attribute must be functionally dependent on the PK
What is the third normal form?
Must be 2NF & all fields must be dependent on the PK
