S EQUENTIAL  P ATTERNS &amp; THE GSP A LGORITHM

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S EQUENTIAL  P ATTERNS &amp; THE GSP A LGORITHM. BY : J OE C ASABONA. I NTRO. What are Sequential Patterns? Why don't ARs suffice? The General Sequential Pattern Algorithm Finding Frequent Sets Candidate Generation Rule Generation. W HAT ARE S EQUENTIAL P ATTERNS ?.

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### SEQUENTIAL PATTERNS & THE GSP ALGORITHM

BY: JOE CASABONA

INTRO
• What are Sequential Patterns?
• Why don't ARs suffice?
• The General Sequential Pattern Algorithm
• Finding Frequent Sets
• Candidate Generation
• Rule Generation
WHATARE SEQUENTIAL PATTERNS?

"Finding statistically relevant patterns between data examples where the values are delivered in a sequence." [3]

Very similar to Association Rules, but sequence in this case matters.

There may be times when order is important.

SEQUENTIAL PATTERN EXAMPLES

In Transaction Processing:

Do customers usually buy a new controller or a game first after buying an Xbox?

In Text Mining:

Order of the words important for finding linguistic or

language patterns [1]

OBJECTIVE

Given a set S of input data sequences, find all sequences that have a user-specified minimum support. This is called a 'frequent sequence' or sequential pattern. [1]

We will use the Generalized Sequential Pattern Algorithm (GSP)

GSP

Similar to Apriori Algorithm

•  Find individual items with minSupport (1-sequences)
• Use them to find 2-sequences
• Continue using k-sequences to find (k+1)-sequences
• Stop when there are no more frequent sequences.

Difference is in Candidate Generation

GSP: CANDIDATE GENERATION

Input : Frequent Set k-1 (F[k-1])

Output: Candidate Set C[k]

How it works:

• Join F[k-1] with F[k-1]
•  Get rid of infrequent sequences (prune)
• Note: Order of items matter
CANDIDATE EXAMPLE

F[3] = <{1, 2} {4}>, <{1, 2} {5}>, <{1} {4, 5}>, <{1, 4} {6}>, <{2} {4, 5}>, <{2} {4} {6}>

After Join: <{1, 2} {4, 5}>, <{1, 2} { 4} {6}>

After Prune: <{1, 2} {4, 5}>

C[4]=  <{1, 2} {4, 5}>

RULE GENERATION

Objective not to generate rules, but it can be done.

Sequential Rule: Apply confidence to  Frequent Sequences

Label Sequential Rules: Replace some elements in X with *

RERERENCES

[1] The Book I am using:

Liu, Bing. Web Data Mining, Chapter 2: Association Rules and Sequential Patterns. Springer, December, 2006

Wikipedia:

[2] "GSP Algorithm." http://en.wikipedia.org/wiki/GSP_AlgorithmJune 3, 2008

[3] "Sequence Mining." http://en.wikipedia.org/wiki/Sequence_miningOct. 30, 2008