Database Definitions

Physical data independence

Refers to the immunity of the conceptual schema to changes in the internal schema.

Logical data independence

Refers to the immunity of the external schemas to changes in the conceptual schema.

Null

Represents a value for an attribute that is currently unknown or is not applicable for this tuple

Derived attribute

Represents a value that is derivable from value of a related attribute, or set of attributes, not necessarily in the same entity type.

Generalization

A bottom-up approach that results in a generalised superclass. If we apply generalisation on entities, we attempt to find similarities between them such as common attributes and relationships.

Composite Key

A candidate key that consists of two or more attributes.

Database system

A collection of application programs that interact with the database along with the DBMS and database itself.

Data model

A collection of concepts that can be used to describe a set of data, the operations to manipulate the data, and a set of integrity constraints for the data.

Application program

A computer program that interacts with the database by issuing an appropriate request (typically an SQL statement) to the DBMS.

Database schema

A description of the database structure.

Candidate key

A minimal superkey for that relation

Attribute

A named column of a relation.

Relation Schema

A named relation defined by a set of attribute and domain name pairs.

Tuple

A row of a relation.

Relational database schema

A set of relation schemas, each with a distinct name.

Database

A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization.

Database Management System (DBMS)

A software system that enables users to define, create, maintain, and control access to the database.

Relation

A table with columns and rows.

rDBMS (or RDBMS)

A term used to refer to a DBMS that uses the relational model.

Specialisation

A top-down approach to defining a set of superclasses and their related subclasses. The subclass is defined on the basis of some distinguishing characteristics of the entities in the superclass.

View

A virtual relation that does not necessarily exist in the database but can be produced upon request by a particular user.

Data Definition Language (DDL)

Allows users to define a database (e.g. create table, foreign key, constraints, create index).

Data Manipulation Language (DML)

Allows users to insert, update, delete, view and retrieve data from the database. The part of a DML that involves data retrieval is called a query language.

Superkey

An attribute, or set of attributes, that uniquely identifies a tuple within a relation

Foreign Key

An attribute, or set of attributes, within one relation that matches the candidate key of some (possibly the same) relation.

Subclasses

Are a distinct subgrouping which must be represented in an ERD. Each member of a subclass is also a member of the superclass.

Simple attribute

Composed of a single component with an independent existence.

Composite attribute

Composed of multiple components, each with an independent existence.

External level

Consists of the users' views of the database.

Cardinality

Describes maximum number of possible relationship occurrences for an entity occurrence participating in a given relationship type.

Participation

Determines whether all or only some entity occurrences participate in a relationship occurrence of the relationship type.

Vertical Partitioning

Distributing the attributes of a relation across a number of (smaller) relations (the primary key is duplicated to allow the original relation to be reconstructed)

Horizontal Partitioning

Distributing the tuples of a relation across a number of (smaller) relations.

Weak entity type

Existence-dependent on some other entity type. Can only identify attributes of weak entity types through relationships with strong entity types.

Single-valued attribute

Holds a single value for each occurrence of an entity type.

Multi-valued attribute

Holds multiple values for each occurrence of an entity type.

Referential integrity

If a foreign key exists, either the value of the foreign key matches the value of the candidate key in the home relation or the value of the foreign key is null.

Superclasses

Include one or more distinct subgroupings of its occurrences, which must be represented in an ERD

Logical Data Model (LDM)

Includes Entities (tables), attributes (columns/fields) and relationships (keys).

Conceptual Data Model (CDM)

Includes High-Level data constructs.

Physical Data Model (PDM)

Includes tables, columns, keys, data types, validation rules, database triggers, stored procedures, domains and access constraints.

Data independence

Makes each level of a database schema immune to changes to lower levels.

Entity integrity

Means that no attribute of a primary key can be null.

Strong Entity Type

Not existence-dependent on some other entity type. Uniquely identifiable using the primary key attribute.

Multiplicity

Number (or range) of possible occurrences of an entity type that may relate to a single occurrence of an associated entity type through a particular relationship.

General constraints

Specified by the user that define or constrain some aspect of the enterprise.

Primary Key

The candidate key that is selected to identify tuples uniquely within the relation.

Conceptual level

The community view of the database. It specifies the information content of the entire database, independent of storage considerations. It represents all entities, their attributes, and their relationships, as well as the constraints on the data, and security and integrity information.

Internal level

The computer's view of the database. It specifies how data is represented, how records are sequenced, what indexes and pointers exist, and so on.

Degree of a relation

The number of attributes it contains.

Cardinality of a relation

The number of tuples it contains.

Cardinality of a relation

The number of tuples it possess

Conceptual modeling

The process of constructing a detailed architecture for a database that is independent of implementation details, such as the target DBMS, application programs, programming languages, or any other physical considerations.

Domain constraints

The value of each attribute in each tuple must be from the domain assigned to this attribute .

Primary Key Constraints

Two distinct tuples in any state of the relation cannot have identical values for all attributes in the key.

Data Manipulation language is:

Used to insert, delete, retrieve, etc data in a database.

Data Definition Language is:

Used to specify data types and structures

ANSI-SPARC architecture

Uses three levels of abstraction: external, conceptual, and internal.

Combination primary key

When more than one column is defined as the primary key

Identify the six main types of constraints on a logical data model.

• required data, • attribute domain constraints, • multiplicity, • entity integrity, • referential integrity, • general constraints.