voc midterm 2 Flashcards

1
Q

many 2 many

A

The maximum multiplicity (i.e. the cardinality) in each direction is “many”

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2
Q

association class

A

association that specifies a many cardinality in the multiplicity constraints of both ends of the association.

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3
Q

derived attributes

A

a value that can be computed by using values in other attributes within a table

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4
Q

junction table

A

for every many to many association in the database that will store all the relationship instances

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5
Q

junction table keys

A

pk is fk from the 2 parents

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6
Q

many to many with history

A

design pattern that allows a many to many associtation to broken up by using an association class that contains a desicrimnator attribute. this allows us to tell the difference between two identical instances with something like a date time stamp.

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7
Q

discriminator attribute

A

allows us to discriminate between the muliple pairing of the same attributes between classes.

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8
Q

functional dependencies

A

an attribute that is dependent on another atribute.

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9
Q

functional determines

A

an attribute that affects the state of another attribute

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10
Q

subkeys

A

an attribute that functionally determines only a subset of the attributes in the table

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11
Q

4 part process to fix subkeys

A

Replace R by two schema, R1 and R2 as described in the following steps.
Assign R1 the attributes in the union of the attributes in the subkey FD. That is R1={W ∪ Z}. Since W→Z, by definition, W is a superkey of R1.
Assign R2 the set of attributes {R - Z}, that is, all the attributes in R except those in Z, the attributes on the right-hand-side of the subkey FD
Both R1 and R2 share W in common. In R1, W is a superkey and in R2 it becomes a foreign key.

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12
Q

lossless join property of a decomposition

A

This property, whereby the information modeled in one database is not lost when the database is redesigned

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13
Q

normalization

A

a procedure or set of procedures to insure a database is well designed. mostly by eliminating duplicate information ie: subkeys

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14
Q

third normal form

A

a well designed db.

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15
Q

null

A

a special constant value in the database represents an absent value

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16
Q

repeated attributes

A

attributes that repeat in the same table ie: phone number, cell phone, home phone, work phone, second phone…

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17
Q

weak entity

A

an class that can not exist on its own. a class within a class. ie: phone class for contact.

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18
Q

multivalued attribute

A

storing mutiple values in an attribute.

an plural attribute

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19
Q

multivalued attribute fix

A
create it own single class that maps to the parents pk. 
ie hobbies in persons becomes a hobby class that maps to the persons class.
20
Q

data integrity

A

insuring that the value entered in each filed of a table is consistent with its attribute domain.
ie: phone number int(10)

21
Q

validations rules

A

rules devised to seperate good data from bad data

22
Q

domain patterns

A

some domains have specific patterns: social security numbers, zip codes, phone numbers, emails (@ .com),

23
Q

enumerated domains

A

a set of constant values
kept in a seperate table
no different from other datatables.
ie: states

24
Q

subclasses or specialization

A

a class that represents a subset of another class type.

25
Q

specialization constraints

A
instead of cardinality a subclass is labeled with specialization constrains along 2 dimensions 
incomplete vs complete
dijoint versus overlapping
26
Q

incomplete or partial

A

only some individuals from a parent class are specialized other only have the general.

27
Q

complete specialization

A

all individuals of a parent class have one or more unique attributes that are not common to a generalize parent class

28
Q

disjoint or exclusive

A

an individual of the parent class may be a member of only one speicialization

29
Q

overlapping

A

an individual of the class can be a member of mor than one specialization subclasses

30
Q

superclass

A

the parent class of the subclass.

31
Q

aggregation

A

class type that is a representation of a system of parts. that can exist without eachother. represented as a diamon and a 1..* relationship. parent is 1..1

32
Q

composition

A

stronger aggregation.
the system can not exist without a member. filled in black diamond.
components can not exist on their own without the parent

33
Q

aggregate functions

A

lets us compute values based on mutliple rowes

34
Q

sum

A

adds up multiple rows

35
Q

group by

A

uses an attribute to partition the aggregate statement by

36
Q

having

A

a condition used in aggregate functions

37
Q

join

A

combining multiple tables in some way

38
Q

natural join

A

combines mulitple tables on a common attribute

39
Q

cross join

A

combines all rows to all rows of another table creating a cartesian product. useless

40
Q

distinct

A

removes duplicates of the specified attribute

41
Q

inner join

A

joining tables based on a specific attribute= to another specific attribute

42
Q

alias

A

changing the name of a table or column

43
Q

outer join

A

includes all the data of the specified side. right outer join or left outer join.

44
Q

functions

A

sometimes the data isnt in the table and must be computed using information in the table
aggregate functions and other functions are examples
Functions for rounding, truncating, converting, and formatting numeric data types.
Functions for concatenating, altering case, and manipulating character data types.
Functions for formatting dates and times, or retrieving the date and time from the operating system.
Functions for converting data types such as date or numeric to character string, and vice-versa.
Functions for supplying visible values to null attributes, allowing conditional output, and other miscellaneous tasks.

45
Q

subqueries

A

a query inside a query.

a way to query information i from the results of another query.

46
Q

union

A

from set R and set S

r union s includes all data from r and everything in s.

47
Q

minus

A

from set r and set s

r minus s includes all data from r that is not in s as well