associative entity

p81

aka composite entity, bridge entity, associative entity

the structure includes - as foreign keys - AT LEAST the primary keys of the tables that are to be linked.

attribute domain

p60

bridge entity

p81

aka composite entity, bridge entity, associative entity

Used to avoid the problems with M:N (many to many) relationships.

Links tables that were originally related in an M:N relationship.

Structure includes: as foreign keys, at least the primary keys of the tables that are to be linked.

candidate key

p64

candidate key

a superkey without unneccesary attributes, a minimal superkey.

closure

p68

closure

the property of relational operators.

the use of relational algebra operators on existing relations (tables) produces new relations.

comoposite entity

p81

composite key

p63

data dictionary

p74

determindation

p62

domain

p61

equijoin

p72

flags

p68

foreign key

p65

full functional dependence

p63

functional dependence

p62

homonym

p74

index

p86

index key

p86

inner join

p72

INNER JOIN

only returns matched records from the tables that are being joined.

join column(s)

p71

JOIN COLUMNS

common columns as the result of a join, (step 2=select)

key

p62

KEY

consists of one or more attributes that determine other attributes.

EX.: an inoice number indentifies all of the invoice attributes such as the invoice date and the customer name.

key attribute

p63

left outer join

p73

LEFT OUTER JOIN

if joinging CUSTOMER and AGENT, yields all the rows from CUSTOMER, even those that do not have a matching value.

linking table

p82

LINKING TABLE

the implementation of a composite entity

A CONNECTOR FOR TWO TABLES

CAN CONVERT M:N to 1:M

inner join

p71

INNER JOIN

returns ONLY matched records from the tables that are being joined.

null

p64

natural join

p71

NATURAL JOIN

links tables by selecting only the rows with common values in their common attributes

three steps

1. a PRODUCT of the tables is created

2. a SELECT is performed on the result

3. a PROJECT is performed to yield a single copy of each attribute, eliminating duplicate columns

null

p64

outer join

p72

OUTER JOIN

returns all matched records plus all the unmatched records leaving the values from the other table as NULL

predicate logic

p59

PREDICATE LOGIC

a mathematical framework where something can be verified as either TRUE OR FALSE

primary key (PK)

p61

PRIMARY KEY

a candidate key selected to uniquely indentify all other attribute values in any given row.

CANNOT CONTAIN NULL ENTRIES

EACH TABLE MUST HAVE ONE

referential ingreity

p66

REFERENTIAL INTEGRITY

means that if the foreign key contains a value, that value refers to an existing valid tuple (row) in another relation.

relational algebra

p68

RELATIONAL ALGEBRA

defines the theoretical way of manipulating tables using 8 operators:

- SELECT

- PROJECT

- JOIN

- INTERSECT

- UNION

- DIFFERENCE

- PRODUCT

- DIVIDE

relational schema

65

RELATIONAL SCHEMA

textual representation of the database tables where each table is listed by its name followed by the list of its attributes in parenthesis.

VENDOR (VEND_CODE, VEND_CONTACT, VEND_AREACODE)

right outer join

p73

RIGHT OUTER JOIN

in a pair of tables to be joined, yields all the rows of the right table, including the ones with no matching values in the other table.

IE: a right outer join of CUSTOMER with AGENT will yield all AGENT rows, including ones that do not have a matching CUSTOMER row.

secondary key

p66

SECONDARY KEY

used strictly for data retrieval purposes.

set theory

p59

SET THEORY

a mathematical science that deals with sets, or groups of things.

BASIS FOR DATA MANIPULATION IN THE RELATIONAL MODEL.

superkey

p63

SUPERKEY

any key that uniquely identifies each row.

an attribute (or collection of attributes) that unique indentifies each entity in a table.

synonym

p74

SYNONYM

the use of different names to describe the same object

i.e., car and auto

system catalog

p74

SYSTEM CATALOG aka DATA DICTIONARY

contains all required metadata.

A detailed system data dictionary that describes all objects within the database, including data about:

- table names

- table's creator and creation date

- number of columns in each table

- the data type associated with each column

- index filenames

0

theta join

p72

THETA JOIN

a join operator that links tables, using an inequality comparison operator in the join condition

( <, >, <=, >= )

tuple

p60

TUPLE

a TABLE ROW

represents a single entity occurance within the entity set.

union-compatible

p69

UNION-COMPATIBLE

when TWO OR MORE ROWS share the same number of columns and when their corresponding columns share the same (or compatible) domains

unique index

p87

UNIQUE INDEX

an index in which the index key:

HAS ONLY ONE VALUE (row) ASSOCIATED WITH IT

SELECT aka RESTRICT

yields values for all rows found in a table that satisfy a given condition.

Can be used to:

- List all the row values

- List ONLY those row values which match criteria

YIELDS HORIZONTAL SUBSET OF A TABLE

PROJECT

yields all values for selected attributes.

VERTICAL SUBSET OF A TABLE.

UNION

combines all rows from TWO tables, excluding duplicate rows.

The tables must have the same attribute characteristics (the columns and domains must be compatible) to be used in a UNION.