Chapt.4.5 Modeling of Features of Dimensions

1
Chapt.4.5 Modeling of Features of Dimensions

• Within a dimension hierarchy, elements at the
  same level may have different attributes
  (properties).
• Consider the Product Groups (PG)
• Car (cc, PS, cyl, fuel)
• Camera (reflex, digital, focal length)
• TV (screensize, audio, color, flat) etc.
• Such specific properties are called Features in
  DWH
• If all elements have the same attributes,
  modelling is trivial, within a common relation.

2
Example of heterogeneous Hierarchy with
Features Dimension Products Brand Prod-Group Mode
l BMW Cars (cc, PS, cyl, fuel) 318 ...
750 Motorcycles Sony Cameras (reflex,
digital, focal length) TVs (screensize, audio,
color, flat) Computers Vaio 451
... Daimler-Chr Cars Buses Trucks
3
Partial Schema for Features
PGProd-Group
1
n
PProducts
belongs
n
n
shows
possessesP,FN,F-Value
m
m
Feature FN, Unit
4
Auxiliary Query for Query Formulation to see the
features of the product-group Car select FN,
Unit from Prod-Group G, shows s, Feature
F where G.name Car and G.PG s.PG
and s.FN F.FN i.e. semantic help for
follow-up query
5
P of engines with 2800 cc select P from
Posesses pos where pos.FN cc and
pos.F-Value 2800
6
Problem F-values have specific Units and
therefore types, e.g. cc, PS, audio, screensize,
How to code, represent F-Value? Ex Cities
belong to countries, which show features like
currency political system VAT-Rate Steuer-Hebe
satz Exercise construct detailed schema for
this
7
MonthM
belongs_T
DTime
Facts
shows_T
P Products
Posesses_TD, FN, F-Value
Feature-TFN, unit
Posesses_PP, FN, F-Value
8
...
Facts
Region
m
m
Prod-GroupPG
belongs_P
P Products
n
shows_P
n
m
Posesses_PP, FN, F-Value
k
Feature-PFN, Unit
9
Typical features for months avg
temperature avg sunshine avg beer consumption
on holidays
Production planing forbeer and icecream
10
Typical Query
S Sales where screensize 17 ? Brand
Sony ?? ( Year 1999 ??? Month Dec ? Year
2000 ? Month Jan)screensize ? restriction on
Product-HierarchyBrand ? ? restriction on
Manufacture-Hierarchy or additional
restriction on Product-HierarchyCombine all
restrictions to get one or a few Query-Boxes on
Base-Cube. Retrieve Query-Boxes only from
Base-Cube, perform 1. Post-filtering 2.
aggregation Problem Restrictions, computations
based on F-Values? Be careful with type
Incompatibilities!