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S EQUENTIAL  P ATTERNS & THE GSP A LGORITHM

S EQUENTIAL  P ATTERNS & 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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S EQUENTIAL  P ATTERNS & THE GSP A LGORITHM

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  1. SEQUENTIAL PATTERNS & THE GSP ALGORITHM BY: JOE CASABONA

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

  3. 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. 

  4. 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]

  5. 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)

  6. 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 

  7. 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 

  8. 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}>

  9. 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 *

  10. 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

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