chapter 4 review Flashcards
t or f: the relational DB model offers a logical view of data?
true
view data logically rather than physically?
relational model
structural and data independence.
resembles a file conceptually?
table
t or f: relational DB model is harder to understand than the hierarchical and network model?
false
logical view of relational DB is based on….
relation
two-dimensional structure composed of rows and columns.
table
t or f: a table contains a group of related entities?
true
one or more attributes that determine other attributes
key
t or f: key roles means if you know the value of attribute A, you can determine the value of attribute B
t
attribute B is functionally dependent on A if all rows in the table that agree in value for A also agree in the value of B, this is def of?
functional dependence
composed of more than one attribute?
composite key
any attribute that is a part of a key
key attribute
any key that uniquely identifies each row
superkey
a superkey without unnecessary attributes
candidate key
each row in a table has its unique identity
entity integrity
no data entry is an example of?
nulls
makes the relational DB work?
controlled redundency
t or f: data within the same DB share the same attributes
true
t or f: redundancy exists only when there is unnecessary duplication of attribute values?
true
an attribute whose values match primary key values in a related table
foreign key
FK contains a value that refers to an existing valid tuple in another relation
referential integrity
key used strictly for data retrieval purposes
secondary key
t or f: many relational database managements enforce integrity rules automatically
true
flags indicate the absence of some values
using flags to avoid nulls
provides a detailed accounting of all tables found within a user-created database
data dictionary
t or f: data dictionary contains all attribute names and characteristics for each table in the system and metadata
true
detailed system data dictionary that describes all objects within the database
system catalog
indicates the use of the same name to label different attributes
homonym
indicates the use of different names to label the same attribute
synonym
relational modeling ideal
1:m
should be rare in any relational DB design
1:1
cant be implemented can be changed into 1:m relationships
m:n
what relation is found in any DB environment?
1:m
sometimes means that entities were not defined properly
1:1
avoid problems inherent to m:n relationship by creating a composite key in which relation?
m:n
controls data redundancy by using common attributes shared by table in the?
FK
t or f: data redundancy is not necessary
false
