ISA 245 Exam 2 Key Terms

External Schema

User view

Tuple/Row/Record

a technical term for a row or record

Set Type

A limited type of one-to-many relationship

Instance

A record within a table

Data Element

A single fact or piece of information

Read-only Access

Ability to read a file without making changes

Read and Write Privileges

Ability to read and modify a file

Concurrency

Allows multiple users access to the same record simultaneously

Relation

Another term for table

Logical Data Independence

Change in logical schema without affecting external schema

Table

Combination of fields

Data Model

Concepts for describing data relationships and constraints

Logical Schema

Conceptual design of a database on paper or a whiteboard

Data Inconsistency

Conflicting copies of the same data

Centralized Database System

DBMS and database stored at a single site that is used by several other systems too

Object-Oriented Data Model

DBMS representing information as objects

Multiuser Database System

DBMS supporting multiple users concurrently

Single-User Database System

DBMS supporting one user at a time

Traditional Models

Data models before the relational model

Distributed Database System

Database and DBMS distributed across connected sites connected by a computer network

Self-describing

Database containing the data and also the metadata which defines and describes the data and the relationships between tables in the database

Internal Model

Database representation seen by the DBMS

Database Logical Design

Defines a database in a data model of a specific database management system

Metadata

Defines data and table relationships in a database

Database Physical Design

Defines internal database storage structure, file organization or indexing techniques

Data Type

Defines the type of data permitted in a field, for example numbers only

Data Isolation

Determines when changes are visible to other users

Heterogeneous Distributed Database System

Different sites use different DBMS software with common data exchange software

Database Management System (DBMS)

Enables users to create and maintain databases

Data Integrity

Ensures data correctness and consistency

Data Uniqueness

Ensures no duplicate entries

Data elements

Facts that represent real-world information

Concurrency Control Strategies

Features allowing simultaneous access to data items

Data Modelling

First step in database design process

Physical Data Independence

Immunity of the internal model to physical model changes

Conceptual Schema

Logical representation of a database

Conceptual Model

Logical structure of the entire database

Database Approach

Manages large amounts of organizational information

Operating System (OS)

Manages the physical level of the physical model

Entity Relationship Diagram (ERD)

Model describing tables, attributes, and relationships

Alternate Key

Non-primary candidate keys

Degree

Number of attributes in a table

Data Redundancy

Occurs when a field needs updating in multiple tables

Unary relationship (recursive relationship)

One in which a relationship exists between occurrences of the same entity set.

Schema

Overall description of a database

Physical Model

Physical representation of the database

Attribute/Column/Field

Principal storage unit in a database

File-based System

Program to manipulate data files

Characteristic Entities

Provide additional information about another table

Network Model

Represents data as record types

Relational Model

Represents data as tables

Hierarchical Model

Represents data in a tree structure

External Model

Represents the user's view of the database

Database Constraint

Restriction on data entry or editing in a table

Homogeneous Distributed Database System

Same DBMS software used at multiple sites

Database

Shared collection of related data for organizational support

Relation/Table/File

Subset of domains characterized by a name

View

Subset of the database

Domain

The original sets of atomic values used to model data; a set of acceptable values that a column is allowed

Database Management Software

Tool to store, manipulate, and retrieve data

Data Independence

User applications immune to data changes

entity set

a collection of entities of an entity type at a point of time

entity type

a collection of similar entities

ternary relationship

a relationship type that involves many to many relationships between three tables. unary relationship: one in which a relationship exists between occurrences of the same entity set.

null

a special symbol, independent of data type, which means either unknown or inapplicable; it does not mean zero or blank

entity

a thing or object in the real world with an independent existence that can be differentiated from other objects

entity relationship (ER) data model

also called an ER schema, are represented by ER diagrams. These are well suited to data modelling for use with databases.

foreign key (FK)

an attribute in a table that references the primary key in another table OR it can be null

key

an attribute or group of attributes whose values can be used to uniquely identify an individual entity in an entity set

Secondary Key

an attribute used strictly for data retrieval purposes

independent entity

as the building blocks of a database, these entities are what other tables are based on

composite attributes

attributes that consist of a hierarchy of attributes

multivalued attributes

attributes that have a set of values for each entity n-ary: multiple tables in a relationship

relationship strength

based on how the primary key of a related entity is defined secondary key an attribute used strictly for retrieval purposes

composite key

composed of two or more attributes, but it must be minimal

Candidate Key

composite key that is unique (no two rows in a table may have the same value) and minimal (every column is necessary)

non-identifying relationship

does not contain the foreign key in the primary key; indicated in an ERD by a dotted line

simple attributes

drawn from the atomic value domains

Atomic Value

each value in the domain is indivisible as far as the relational model is concerned

EID

employee identification (ID)

Cardinality

expresses the minimum and maximum number of entity occurrences associated with one

integrity constraints

logical statements that state what data values are or are not allowed and which format is suitable for an attribute

n-ary

multiple tables in a relationship

business rules

obtained from users when gathering requirements and are used to determine cardinality

mandatory relationship

one entity occurrence requires a corresponding entity occurrence.

entity integrity

requires that every table have a primary key; neither the primary key, nor any part of it, can contain null values

recursive relationship

same as unary relationship, multiple tables in a relationship

stored attribute

saved physically to the database

derived entities

see dependent entities

entity relationship schema

see entity relationship data model

kernel

see independent entity

single-valued attributes

see simple attributes

SIN

social insurance number

optional relationship

the FK can be null or the parent table does not need to have a corresponding child table occurrence

relationships

the associations or interactions between entities; used to connect related information between tables

connectivity

the relationship between two tables, e.g., one to one or one to many

constraints

the rules that force DBMSs to check that data satisfies the semantics

dependent entities

these entities depend on other tables for their meaningderived attributes: attributes that contain values calculated from other attributes

identifying relationship

where the primary key contains the foreign key; indicated in an ERD by a solid line

Logical Design

where you create all the tables, constraints, keys, rules, etc.