Glossary Flashcards
Key Words and Definitions
Data
Stored representations of objects and events that have meaning and importance.
Information
Data that has been processed in such a way as to increase knowledge of the person who uses it.
Database
An organised collection of logically related data.
Entity
A person, a place, an object, an event, or a concept in the user environment about which the organisation wishes to maintain data.
Relational Database
A database that represents data as a collection of tables in which all data relationships are represented by common values in related tables.
Database Management System (DBMS)
A software system that is used to create, maintain, and provide controlled access to a user database.
Entity Relationship Model
A logical representation of the data for an organisation or for a business area, using entities for categories of data and relationships for associations between entities.
Entity Relationship Diagram (ERD)
A graphical representation of an Entity Relationship Model.
Business Rule
A statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behaviour of the business.
Identifier / Primary Key
An attribute (or combination of attributes) whose value distinguishes instances of an entity type.
Foreign Key
An attribute in a relation that serves as the primary key of another relation in the same database.
Schema
A structure that contains description of objects created by a user, such as base tables and constraints as part of a database.
Structured Query Language (SQL)
SQL is the language used by all DBMS’s.
Entity Instance
A single occurrence of an entity type.
Referential Integrity Constraint
A rule that states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null.
Cardinality Constraint
A rule that specifies the number of instances of one entity that can (or must) be associated with each instance of another entity.
Minimum Cardinality
The minimum number of instances of one entity that may be associated with each instance of another entity.
Maximum Cardinality
The maximum number of instances of one entity that may be associated with each instance of another entity.
Data Definition Language (DDL)
Commands used to define a database, including those for creating, altering, and dropping tables and establishing constraints.
Data Manipulation Language (DML)
Commands used to maintain and query a database, including those for updating, inserting, modifying, and querying data.
NULL
A value that may be assigned to an attribute when no other value applies or when the applicable value is unknown.
Data Redundancy
This is a condition created within a database or data storage technology in which the same piece of data is held in two separate places. Relations that have redundant data have data anomalies, which are classified as:
- Insertion anomalies
- Deletion anomalies
- Update/Modification anomalies
Anomaly
An error or inconsistency that may result when a user attempts to update a table that contains redundant data.
Constraint
A rule that cannot be violated by database user.
Strong Entity Type
An entity that exists independently of other entity types.
Weak Entity Type
An entity type whose existence depends on some other entity type.
Relationship Type
A meaningful association between (or among) entity types.
NOT NULL Constraint
The NOT NULL constraint enforces a column to NOT accept NULL values.
UNIQUE Constraint
The UNIQUE constraint ensures that all values in a column are different.
CHECK Constraint
The CHECK constraint is used to limit the value range that can be placed in a column.
Multi Valued Attribute
An attribute that may take on more than one value for a given entity (or relationship) instance.
SQL Sub-Queries
A sub-query is a SQL query nested inside a larger query.
SQL Views
In SQL, a view is a virtual table based on the result-set of an SQL statement. A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.
Ternary Relationship
A simultaneous relationship among the instances of three entity types.
