Multilevel Mining Association Rules:
- Items often form hierarchy.
- Items of the lower level are expected to have lower support.
- A common form of background knowledge as that an attribute may be generated or specialized according to a hierarchy of concepts.
- Rules which contain associations with hierarchy of concepts are called Multilevel Association Rules.
Support and confidence of Multilevel association rules:
- Generalizing / specializing values of attributes affects support and confidence.
- Support of rules increases from specialized to general.
- Support of rules decreases from general to specialized.
Confidence is not affected for general or specialized.
Two Approaches of Multilevel Association Rules:
I. Using uniform support level for all levels:
- The same minimum support for all levels.
- There is only one minimum support threshold so no need to examine itemsets
- If support threshold is too high ⇒ miss low level associations
- If the support threshold is too low ⇒ generate too many high level associations.
Fig: Example of uniform minimum support for all levels
II. Using reduced minimum support at lower level:
At every level of abstraction , there is its own minimum support threshold
So minimum support at lower levels reduces.
Fig: Example of reduced minimum support for lower level