Database
A collection of related data
Data
Known facts that can be stored and have an explicit meaning
Mini-world
Some part of the real world about which data is stored in a database.
DBMS
Database Management System
A software package/system used to facilitate the creation and maintenance of a computerized database.
Database System
The DBMS software together with the data itself
Data abstraction
A conceptual view of the database where the data storage details are hidden
What are the advantages of using a database solution compared to the traditional file storage mechanism?
-improved data organisation: organise data in a structured way making it easier to retrieve, update and manage data.
- data security, restricted unauthorized access, authentification, encryption.
- data sharing among multiple users
- data integrity and consistency through constraints and Referential integrity
- scalability: can handle large amount of days and scale back or up as needed
What is the role of a DBMS
A DBMS is a software system that allows users to define, create, maintain, and control access to a database.
It acts as an intermediary between the user and the database, handling storage, retrieval, and management of data.
What is the Three-Schema architecture?
A design approach for database management systems that sperates the database into three independent schemas:
- the external schema: describes the different user views
- the conceptual schema: describes the structure and constraints of the whole database for a community of users at a conceptual level
- the internal schema: describes the physical storage structure and the data access paths
The external schema
Describes how each individual user or group of users views the data and provides an interface for accessing the data.
The conceptual schema
Represents the overall logical structure of the entire database.
It describes the entities, relationships and constraints of the data in a way that is independent of any particular application or user
The internal schema
Describes the physical storage structure of the database.
It defines how the data is stored on disk and the data access paths used to retrieve the data.
The Three-Tier Client-Server Architecture
A design approach used in software systems, where the system is divided into the tiers:
- the presentation tier
- the application tier
- the data tier
What is a data model?
A set of concepts to describe:
- the structure of a database
- the operations for manipulating these structures
- the constraints that the database should obey
What is the difference between the Three-Schema Architecture and the Three-Tier Client-Server Architecture?
The two architectures are two different concepts in software architecture. They describe different aspects of structures and for different systems.
- The Three-Schema Architecture used to represent data in a database System. It consists of three levels of schema:
- the external schema: the user interface layer which is used to present data to users.
- the conceptual schema: the logical layer which defines the relationships between data.
- The internal schema: the physical layer which defines how data is stored and accessed by the system. - The Three-Tier Client-Server Architecture is a software architecture that separates the application into three layers:
- The presentation layer: responsible for presenting the user interface to the user.
- The application layer: contains the business logic of the application.
- The data layer: responsible for storing and retrieving data.
The main difference between the two architectures is that the Three-Schema architecture is focused on the organization and representation of data while the Three-Tier Client-Server Architecture is focused on the organization of the software components in an application
What are the different types of database users?
- The actors on the scene: those who use and control the database content as well as those who design, develop and maintain database applications.
- The workers behind the scene: those who design and develop the DBMS software and related tools, as well as the computer systems operators
Superkey
A set of one or more attributes that can uniquely identify each tuple in a table.
A superkey can contain more attributes than are minimally required to uniquely identify each row and it can include attributes that are not strictly necessary for identification purposes.
Key
A key is a superkey that has the additional condition that removing any attribute from the key would result in a set of attribute that is no longer a superkey. No longer unique
Candidate key
A set of one or more attributes that can be used as a primary key.
AKA a potential key.
Database schema
The description of a database:
- structure
- data types
- the constraints on the database
Database state
The actual data stored in a given database at a particular moment in time. This includes the collection of all data in a database
Primary key
A candidate key that has been selected as the main key of the relation. It uniquely identify each tuple in that relation and cannot be null
Foreign key
An attribute in a relation that refers to the primary key of another relation. It establishes a relationship between the two relations
Degree of relationship type
The degree of a relationship type refers to the number of entity types that participates in a relationship.
Binary, ternary, n-ary
