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Data Warehousing
Data warehousing
21
Computer Science
Graduate
07/20/2010

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Cards

Term
Degenerate Keys
Definition

are equivalent to dimension keys of a fact, with the exception that there is no other dimension information associated with a degenerate key. Degenerate keys are used in data analysis processes to group facts together.

Term
degenerate DIMENSIONS
Definition
 is a dimension that is stored in the fact table rather than the dimension table. It eliminates the need to join to a Dimension table.
Term

fact attributes

 

Non-additive

Definition
  1. – facts cannot be aggregated across any dimension (degenerate)
Term

fact attributes

 

Additive

Definition
facts (or measures) can be summed, averaged (aggregated) across all dimensions
Term

Fact attributes

 

Semi-additive or Snap shot fact

Definition

Inventories can be averaged but not summed. Can be aggregated across some, but not all dimensions. How can you tell the difference between a snap-shot star schema

Term

Fact attributes

Factless fact table

Definition
contains no measures than can be aggregated
Term
Conformed dimensions
Definition

Conformed dimensions are those that are used in multiple star schemas.  The dimensions are referenced by the same name and the attributes are also referenced by the same name.

Term

slowly changing dimensions

 

Overwrite the value

Definition
type 1
Term

Slowly changing dimensions

 

Add a dimension column

 

Definition
Type 3
Term

Slowly changing dimensions

 

Add a dimension row

Definition
type 2
Term
Role-playing dimension
Definition
Dimensions are often recycled for multiple applications within the same database. For instance, a "Date" dimension can be used for "Date of Sale", as well as "Date of Delivery", or "Date of Hire". This is often referred to as a "role-playing dimension".
Term
Mini Dimension
Definition
a Primary Key that is part of the composite key of the fact table, good for very large rapidly changing dimension tables
Term
Outrigger
Definition
Primary Key is a foreign key in the related dimension table, not the fact table
Term

Know the SQL (DDL) to Create tables and apply constraints

Definition

CREATE TABLE course

(courseNo VARCHAR(10),

title VARCHAR(20),

Instructor VARCHAR(20),

CONSTRAINT Course_PK PRIMARY KEY (CourseNo),

CONSTRAINT course_FK1 FOREIGN KEY (Instructor) RFERENCES Instructor(Instructor name)

) go

Term

Know the SQL (DDL) to Create sequences

Definition
create sequence sessiondateSeq start with 1 increment by 1 nomaxvalue
go
Term

Know the SQL for INSERTing records in a table

Definition

INSERT INTO teachingassistant table VALUES

(030, 3490928, 0303) go

Term

Know the SQL to INSERT data from a SELECT statement

Definition
INSERT california_authors (au_id, au_lname, au_fname)
SELECT au_id, au_lname, au_fname
FROM authors
WHERE State = 'CA'
Term
b-tree
Definition
is better for higher cardinality attribute values and is very fast.  On the downside, though, it uses more memory
Term
Bitmap
Definition
best for low cardinality attributes, where possible answers are few (boolean is best). 
Term

AGGREGATES

 

Fact table aggregates

Definition
Aggregates base-level fact data across one or many dimensions
Term

AGGREGATES

Dimension table aggregates

 

Definition
Summarizes dimension data along a single attribute such as CITY or STATE.
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