Database

Enterprise-class database

A DBMS product capable of supporting the operating requirement of large organizations

personal database system

A DBMS product intended for use by an individual or small work-group. such products typically include application development tools such as form and report generators in addition to the DBMS. for example Microsoft access 2013

relational model

A data model in which data are stored in relations and relationships between rows are represented by data values

table

A database structure of rows and columns to creat cells that hold data values. also known as relation in a relational database, although strictly only tables that meet specific conditions can be called raltions

relational database

A database that consists of relations. in practice, relational databases contain relations with duplicate rows. most DBMS products include a feature that removes duplicate rows when necessary and appropriate. such as removal is not done as a matter of course because it can be time-consuming and expensive

structured query language (SQL)

A language for defining the structure and processing of a relational database. it can be used as a stand alone query language, or it can be embedded in application programs. SQL was developed by IBM and is accepted as a national standard by the american national standards institute

referential integrity constraint

A relationship constraint on foreign key values. a referential integrity constraint specifies that the values of a foreign key must be a proper subset of the values of the primary key to which it refers

database management system (DBMS)

A set of programs used to define, administer and process a database and its applications

Tuple

Same as Row

primary key

a candidate key selected to be the key of a relation

question mark (?)

a character used in microsoft access 2013 queries to represent a single unspecified character

database schema

a complete logical view of a database

Multivalued dependency

a condition in a relation with three or more attributes in which independent attributes appear to have relationships they do not have.

row

a group of columns in a table. All the columns in a row pertain to the same entity. also known as tuple or record.

record

a group of fields pertaining to the same entity; used in file processing systems. in the relational model, a synonym for row and tuple

Key

a group of one or more attributes that identify a unique row in a relation. because relation. because relations cannot have duplicate rows, every relation must have at least one key that is the composite of all the attributes in the relation. a key is sometimes called a logical key. with some relational DBMS products, an index on a column used to improve access and sorting speed. it is sometimes called a physical key.

composite key

a key of a relation that consists of two or more columns

unique key

a key that identifies a unique row

nonunique key

a key that potentially identifies more than one row

data sublanguage

a language for defining and processing a database intended to be embedded in programs written in another language

Data manipulation language (DML)

a language used to describe the processing of a database

Data definition language (DDL)

a language used to describe the structure of a database

field

a logical group of bytes in a record used with file processing. in the context of the relational model a synonym for attribute

column

a logical group of bytes in a row of a relation or a table. the meaning of a column is the same for every row of the relation

Extensible markup language (XML)

a markup language whose tags can be extended by document designers

fifth normal form

a normal form necessary to eliminate an anomaly where a table can be spilt apart but not correctly joined back together. also known as project join normal form

fourth normal form

a relation in BCNF in which every multivalued dependency is a functional dependency

second normal form

a relation in first normal form in which all non key attributes are dependent on all the keys

third normal form

a relation in second normal form that has no transitive dependencies

Boyce-Codd Normal Form (BCNF)

a relation in third normal form in which every determinant is a candidate key

domain key / normal form

a relation in which all constraints are logical consequences of domains and keys. in this test this definition has been simplified to a relation in which the determinants of all functional dependencies are candidate keys

SQL view

a relation that is constructed from a single SQL select statement SQL views have at most one multivalued path.

Functional dependency

a relationship between attributes in which one attribute or group of attributes determines the value of another

referential integrity contraint

a relationship constraint on foreign key values. a referential integrity constraint specifies that the values of a foreign key must be proper subset of the values of the primary key to which it refers

subquery

a select statement that appears in the Where clause of an SQK statement. subqueries can be nested within each other

Database

a self-describing collection of related records or for relational databases of related tables

business rule

a statement of a policy in a business that restricts the ways in which data can be inserted, updated, or deleted in the database

Form

a structured on-screen presentation of selected data from a database. forms are sued for both data input and data reading. a form is part of a database application. compare this with a report

query by example

a style of query interface first developed by IBM but now used by other vendors that enables users to express queries by providing examples of the results they seek

relation

a two dimensional array that contains single value entries and no duplicate rows. the meaning of the columns is the same in every row. the order of the rows and columns is immaterial

surrogate key

a unique, system supplied identifier used as the primary key of a relation. the values of a surrogate key have no meaning to the users and usually are hidden on forms and reports

Attribute

a value that represents a characteristic of an entity a column of a relation

Candidate key

an attribute or a group of attributes that identifies a unique row in a relation. one of the candidate keys is chosen to be the primary key

foreign key

an attribute that is a key of one or more relations other than the one in which it appears

null value

an attribute value that has never been supplied. such values are ambiguous and can mean the value is unknown, the value is not appropriate, or the value is known to be blank

first normal form

any table that fits the definition of a relation

metadata

data concerning the structure of data in a database stored in the data dictionary. Metadata are used to describe tables, columns, constraints, indexes, and so forth

MAX

in SQL a funciton that determines the largest value in a set of numbers

MIN

in SQL a funciton that determines the smallest value in a set of numbers

COUNT

in SQL a function that counts the number of rows in a query result

transitive dependency

in a relation having at least three attributes such as R (A,B,C) the situation in which a determines b and b determines C but B does not determine A.

SUM

in sql a funciton that adds up a set of number

SQL built in function

in sql any of the functions count sum avg max or min

determinant

one or more attributes that functionally determine another attribute or attributes. in the functional dependency (A,D) > D,C the attributes (A,B) are the determinants

entity

somethin gof importance to a user that needs to be represented in a database. in the entity relationship model entities are restricted to things that can be represented by a single table

American National Standards Institute (ANSI)

the american standards organization that creates and publishes the SQL standards

SQL select/from/where framework

the basic structure of an SQL query

SQL Where Clause

the part of an SQL select statement that specifies conditions used to determine which rows are in the query results

SQL from clause

the part of an SQL select statement that specifies conditions used to determine which tables are used in a query

SQL select clause

the part of an sql select statement that specifies which column are in the query results

normalization process

the process of evaluating a relation to determine whether it is in a specified normal form and if necessary of converting it to relations in that specified normal form

SQL create table

the sql command used to create a database table