Date of Award


Publication Type

Master Thesis

Degree Name



Computer Science


Data mining, Web Mining, Association Rule Mining, Long Sequences, PLWAP Mining, Applied sciences


Christie I. Ezeife




Sequential pattern mining is the process of finding inter-transaction frequent sequential patterns from a sequential database, where records consist of ordered sets of events (or items), by applying data mining techniques on such sequential databases. Discovering sequential patterns in web server logs is an example application of sequential mining, which is useful for predicting visiting patterns of web users for such purposes as targeted advertisements. Position Coded Pre-order Linked Web Access Pattern (PLWAP) mining algorithm is one of the existing efficient web sequential pattern mining algorithms, which stores the frequently stored sequences of the entire sequential database in a compressed tree form with position coded nodes.

However, for very long sequences exceeding thirty two nodes, the number of bits an integer position code can hold, the PLWAP algorithm's performance begins to degrade because it employs linked lists to store conjunctions of long position codes and the linked list traversals slow down the algorithm both during tree construction and mining. PLWAP algorithm also uses each and every node in the frequent 1-item event queue to test for that event inclusion in the suffix tree root set during mining. This is a very expensive operation since except for one node all other nodes that are its ancestors and descendents are not included in the root set.

This thesis proposes two new algorithms, i.e. PLWAPLong1 and PLWAPLong2. Both of these new algorithms use a new position code numbering scheme where each node is assigned two numeric variables (startPosition, endPosition) instead of one. Using this scheme we can determine the ancestor node in O (1) operation by comparing the startPosition and endPosition of two nodes. PLWAPLong1 algorithm also proposes transforming the linked list based tree to an equivalent array representation and using binary search to find the immediate descendant in a suffix tree. PLWAPLong2 uses existing linked list based tree. Both PLWAPLong1 and PLWAPLong2 algorithms introduce a new technique called "Last Descendant" to eliminate the unwanted nodes from ancestor/descendent test when creating the suffix tree root set.

Keywords: Data mining, Web Mining, Association Rule Mining, Long Sequences, PLWAP Mining