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database final Flashcards

1
Q

entity is what

A

is some identifiable thing that users want to track

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2
Q

functional dependency

A

occurs when the value of one set of attributes determines the value of a second set of attributes

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3
Q

what is an example of functional dependency

A

studentID is a determinent of studentName

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4
Q

composite determinant

A

a determinant of a functional dependency that consists of more than one attribute for example student name and class name to determine grade

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5
Q

compostie key

A

is a key that consists of two or more columns

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6
Q

candidate key

A

is a key that determines all of the other columns in a relation from the candidate keys the designer selects one to be the PK

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7
Q

primary key

A

is a candidate key selected as the primary means of uniquely identifying a row in a relation

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8
Q

Surrogate Key

A

is an artificial column added to the relation to serve as the primary key this is created when a good PK cannot be found.

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9
Q

foreign key

A

is the primary key of one relation that is placed in another relation to for a link between the relations.

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10
Q

referential integrity constraints

A

is a statement that limits the values of the foreign key to those already existing as primary key values in the corresponding relation.

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11
Q

what is BSNF

A

boy scott normal form this is how every database should be performed

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12
Q

select statement

A

select
from
where
;

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13
Q
  • in sql
A

means to select all columns

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14
Q

sql built in functions

A

count, sum, avg, min, max

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15
Q

quering multiple tables

A

must use joints by stateing the table and its fk = to table the the pk

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16
Q

how do you create a table in sql

A

use create table statement but dont specify any of the FK’s untill all tables have been created and the data has been input also makeing fk’s null makes life easier

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17
Q

alter table

A

used when inputing new column or fk’s

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18
Q

insert command

A

used to insert values into a table

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19
Q

update command

A

is used most often when you want to update an entry

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20
Q

data model

A

is a plan or blueprint for a database design

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21
Q

entity-relationship model

A

is a set of concepts and graphical symobols that can be used to create conceptual schemas.

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22
Q

what is and entity is a relationship model

A

this is a thing in which you want to store data like students, or employee, or courses

23
Q

an attribute in entity relationship model

A

is what describes and entity characteristics these are the columns in the table

24
Q

identifiers

A

are attributes that name or identify entity instances or the primary key these can be composite where it consists of 2 or more attributes

25
Q

binary relationship

A

is a relationship that is between 2 enteties

26
Q

a ternary relationship

A

is a relationship that is between 3 enteties

27
Q

maximum cardinality

A

is the max number of entity instances that can participate in a relationship

28
Q

minimum cardinality

A

is the minimum number of entity instances that must participatein a relationship

29
Q

what are the types of max cardinality

A

one to one, one to many, many to many

30
Q

what is the parent entity

A

this is the entity that is one the one side of the relationship

31
Q

what is the child entity

A

this is the entity on the many side of the relastionship

32
Q

minimum cardinality

A

is the minimum number of entity instances that must participate in a relationship this must be ether zero or 1

33
Q

strong entity

A

is one that represents something that can exist on its own. for example department and employee represented by a dashed line.

34
Q

weak entity

A

is one whose existance depends on the presence of another entity

35
Q

ID-dependent entity

A

is an entity whose identifier includes the identifier of another entity. the minimum cardinality for this is always one. all id dependent entities are considered weak entities.

36
Q

supertype entity

A

contains all common attributes for example the super type might be patient

37
Q

the subtype entity

A

contains specific attributes also may have a discriminator attribute which indicates the subtype the sub type would be male or female and the discriminator is sex

38
Q

exclusive subtype

A

means that the supertype can at most relate to one subtype

39
Q

an inclusive subtype

A

means at most the supertype can relate to one or more subtypes.

40
Q

a recursive relationship

A

is when the entity has a relationship to itself

41
Q

1st step in creating data mode

A

create a table for each entity, specify the PK, the candidate keys, and the properties of each column i.e. null data type

42
Q

second set in creating data model

A

create relationships by placing foreign keys, relastionships between sstrong entities, identifying relationships with ID-denpendencies , and relationships between strong and weak entities

43
Q

step 3 in creating data model

A

specify logic for enforcing minimum cardinality i.e. many to many , one to one, or one to many

44
Q

DBA’s tasks

A

manage database structure, control concurrent processing, manage processing rights and responsibilities, develop database recovery, manage DBMS maintain the data repository

45
Q

a transaction

A

is a series of actions taken agains the database that occurs as an atomic unit. either all occur or none of them do.

46
Q

concurrent transaction

A

refers to two or more transactions that are being processed against a database at the same time

47
Q

implicit locks

A

are locks placed by the DBMS

48
Q

explicit locks

A

are issued by the application program

49
Q

exclusive lock

A

prohibits other users from reading the locked resource

50
Q

shared lock

A

allows other users to read the locked resource but they cannot update it

51
Q

deadlock

A

occurs when transactions are each waiting on a resource that the other transaction holds.

52
Q

preventing dead locks

A

allow users to issue all lock requests at one time repuire all application programs to lock resources inn the same order.

53
Q

breaking deadlocks

A

almost every dbms has algorithms for etecting deadlock when deadlock occurs dbms aborts one of the transactions and rollbacks partialy completed work

database (2 decks)

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