The cube and OLAP operations
The data cube (cell, dimension, level, member) and its operations: roll up, drill down, slice, dice, pivot; the three storages MOLAP, ROLAP and HOLAP.
- 33 cards
- 5 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- The numbers
- Understand
A few cards from the deck
OLAP: what is it?
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A family of interactive analysis tools that presents measures along several axes and lets users move through the results from one level of detail to another.
It contrasts with OLTP, which handles day-to-day transactions. OLAP reads many rows to summarise them, and changes almost nothing.
We go from 'sales by month and city' to 'sales by quarter and city'. Which operation is it?
- A roll-up on the time dimension
- A drill-down on the time dimension
- A slice on the first quarter
- A pivot of the time dimension
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A roll-up on the time dimension
Months are grouped into quarters, a coarser level of the same hierarchy: that is a roll-up. A drill-down does the opposite, a slice would remove the dimension, a pivot would change no value.
In a sales cube, the … are the axes of analysis (product, time, place) and the … is the value being aggregated (the amount).
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In a sales cube, the dimensions are the axes of analysis (product, time, place) and the measure is the value being aggregated (the amount).
Dimensions describe, the measure is counted. A cell crosses one member of each dimension and carries the measure.
Data cube: what is it?
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A multidimensional structure whose every cell holds a measure (a sales amount) at the intersection of one member of each dimension (a product, a month, a city).
The word 'cube' suits three dimensions, but a cube can have more. A cell is located by one member per dimension.