DATA WAREHOUSING Multi Dimensional Data Modeling Hierarchies and Levels

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customer custId name address city

53 joe 10 main sfo

81 fred 12 main sfo

111 sally 80 willow la

product prodId name price

p1 bolt 10

p2 nut 5

store storeId city

c1 nyc

c2 sfo

c3 la

sale oderId date custId prodId storeId qty amt

o100 1/7/97 53 p1 c1 1 12

o102 2/7/97 53 p2 c1 2 11

105 3/8/97 111 p1 c3 5 50

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Group data within dimensions: SalesRep

Region

▪ SubRegion ▪ Country

Customer

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Hierarchies are logical structures that use ordered levels as a means of organizing data.

For a particular level value, a value at the next higher level is its parent, and values at the next lower level are its children

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Hierarchies impose a family structure on dimension values. For a particular level value, a value at the next higher level is its parent, and values at the next lower level are its children.

These familial relationships enable analysts to access data quickly.

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A dimension can be composed of more than one hierarchy.

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time day week month quarter year

1 1 1 1 2000

2 1 1 1 2000

3 1 1 1 2000

4 1 1 1 2000

5 1 1 1 2000

6 1 1 1 2000

7 1 1 1 2000

8 2 1 1 2000

days

weeks months

weeks

years

quarters

months

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Query tools use hierarchies to enable you to drill down into your data to view different levels of granularity.

This is one of the key benefits of a data warehouse.

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When designing hierarchies, you must consider the relationships in business structures. For example, a divisional multilevel sales organization.

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A level represents a position in a hierarchy. For example, a time dimension might have a hierarchy that represents data at the month, quarter, and year levels.

Within a hierarchy, each level is logically connected to the levels above and below it.

time day week month quarter year

1 1 1 1 2000

2 1 1 1 2000

3 1 1 1 2000

4 1 1 1 2000

5 1 1 1 2000

6 1 1 1 2000

7 1 1 1 2000

8 2 1 1 2000

years

quarters

months

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The levels in a dimension are organized into one or more hierarchies.

months

weeks

years

quarters

months

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Levels range from general to specific, with the root level as the highest or most general level.

all

years

quarters

months

days

weeks

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Level relationships specify top-to-bottom ordering of levels from most general (the root) to most specific information.

They define the parent-child relationship between the levels in a hierarchy.

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store storeId cityId tId mgr

s5 sfo t1 joe

s7 sfo t2 fred

s9 la t1 nancycity cityId pop regId

sfo 1M north

la 5M south

region regId name

north cold region

south warm region

sType tId size location

t1 small downtown

t2 large suburbs

store city region

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The Data Warehouse Toolkit.Second Edition.The Complete Guide to Dimensional Modeling.Ralph Kimball.Margy Ross