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Systems Chapter 4
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Objective of logical base design
to transform the conceptual data model into a set of relations used for physical database design
Three components of a relational data model
-Relational data structure
: where data is stored
-Data Manipulation
: operations used to manipulate data in the data structure
-Relational Data Integrity
: rules that maintain integrity of the data when manipulated
Relation
the main data structure that stores and organized data in the relational data model
- Column = attribute
- Row = record/tuple
Properties of a Relation
-Each relation is uniquely identified by its name
-Each cell of a relation contains exactly one (atomic) value
-Each record of a relation is unique
-Each attribute in a relation has a distinct name
-The values of an attribute are from the same domain
-The order of attributes is irrelevant
-The order of records is also irrelevant
Composite Key
key with more than one attribute
Super Key
is a set of one or more attributes that uniquely identifies each record in a relation
Candidate Key
is a minimal super key (minimum number of attributes)
Primary Key
a candidate key that has been selected to uniquely identify records in a relation
Primary Key Properties
-Must be unique within its domain at all times
-The candidate key can never change
-It cannot hold a NULL value
Foreign Key
attribute or set of attributes in a relation that serves as a primary key of the same or some other relation
Three Types of Data Integrity Constraints
-Domain Constraints
: all values of an attribute must be from the same domain
-Entity Constraints
: ensure that every relation of a relational data model has a primary key and that it is not null
-Referential Constraints
: assures consistency between two relations that are linked through the primary key-foregin key relationship
Domain
set of values that can be assigned to an attribute
Normalization
refers to a series of tests performed on relations to determine whether they satisfy or voilate the requirements of a normal form
Data Redundancy
having duplicate data in the database
-Increases storage use
-Reduces efficiency of data updates
Anomalies
inconsistency problems caused by relations with redundant data
Insertion Anomalies
Abnormalities encountered while inserting new records into the relation
Deletion Anomalies
occur when data had been unintentionally removed from the relation
Update Anomalies
occur when there are multiple changes required to reflect a single attribute change
Functional Dependency
a relationship among attributes with a RELATION
Determinants
Attributes on the left-hand side of the arrow in a functional dependency representation
-if all attributes appear in the functional dependency representation then the determinant is the super key
Dependency Diagram
a pictorial representation of a functional dependency
Partial Dependency
functional dependency in which a non-primary key's attributes functionally depent of a part of (but not all) the primary key attributes
Transitive Dependency
functional dependency in which a none of the attributes involves attributes of a primary key
First Normal Form
each cell in the relation contains exactly one value
Second Normal Form
-Already in first normal form
-No partial functional dependencies
Third Noral Form
-Already in second normal form
-No transitive dependencies
Boyce-Codd Normal form
-Already in third normal form
-Every deteminant is a candidate key
Author
rinkboy36
ID
66699
Card Set
Systems Chapter 4
Description
Chapter 4
Updated
2011-02-16T14:18:03Z
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