Chapter 4-Database Design Methodology Flashcards
Insertion anomaly
A circumstance in which data may not be entered into a relation because a complete primary key is not available.
Deletion anomaly
A circumstance in which unwanted data is deleted from my relation.
Update anomaly
A circumstance in which redundant data in a relation may not be properly updated.
Name the six conceptual design phases.
- Identifying entities.
- Identifying attributes and attribute domains for entities.
- Identifying relationships.
- Identifying candidate and primary keys for entities.
- Creating an entity relationship diagram.
- Reviewing the ER model by the design user and design team.
Each entity must have what to distinguish it from other entities?
A unique identifier
Once each entity has been identified and given a unique identifier what needs to happen next?
The attributes or characteristics of each entity must be identified.
What needs to happen with the primary key during the identifying candidate and primary keys for entities phase?
The step involves determining which attribute with an entity will be used as the primary key.
What are the four guidelines to use when determining a primary key?
- The candidate key least likely to have its value changed.
- The candidate key least likely to lose its uniqueness.
- The candidate key that contains the fewest characters.
- The candidate key that is easiest for the user to use.
What is another style of database modeling?
Information engineering (IE)
In an ER model what shape is used to represent entities?
Rectangle
In an ER model what shape is used to represent attributes?
Oval
In an ER model what indicates the primary key?
*
In the IE model the attributes are placed within what?
A rectangle
SMALLINT
16 bit signed integer
INTEGER
32 bit signed integer
DECIMAL(p,q)
Signed decimal number, p is digits and q is decimals.
FLOAT(p)
Floating-point number of p bits Percision
CHAR(n)
Fixed length string of n characters
VARCHAR(n)
Variable length string of up to n characters
DATE
Date in the form YYYYMMMDD
TIME
Time in the form HH MM SS
TIMESTAMP
Combines a DATE and a TIME
Recursive relationship
An entity relationship in which an entity is involved in a relationship with itself.
CREATE TABLE
Tables created with CREATE TABLE statement are based tables.
Methodology
An organized documented set of procedures and guidelines for those who work in a discipline or participate in an inquiry.
