Relational Data Model Flashcards
enable programmer to view data logically, rather than physically
Relational Model
advantage of data and structural independence.
easier to understand than hierarchical and network dbase predecessors.
resembles file from conceptual view
Table
Related entities
Entity set
specific Range of values for each column
Attribute domain
is one or more combination of attributes that uniquely identifies any given Entity(row)
Primary keys
composed of more thna one attribute
Composite key
any attribute that is part of key
unique characteristic of entity
Key attribute
key that uniquely identifies each row
Super key
superkey w/o redundancies
Candidate Key
no data entry
not permitted in primary key
should be acoided in other attributes
represents: unknown attr value,known but missing, not applicable
Null
makes relational dbase work
redundancy exists only when there is unnecesary duplication of attr values
Controlled redundancy
attribute whose values match primary key values
Foreign Keys
for data retrieval process
Secondary key
manipulating table contents using relational operators
Relational Algebra
combine all rows from two tables, excluding duplicates
UNION
