wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (04/13/89)
DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES REVISED ROOM CHANGE! DATA STRUCTURES SEMINAR -Monday, April 17, 1989 Mr. Ricardo Baeza-Yates will speak on "Searching Regular Expressions". TIME: 3:30-5:30 PM ROOM: DC 1302 ABSTRACT We present algorithms for efficient searching of regular expressions on preprocessed text. We obtain logarithmic (in the size of the text) average time for a wide subclass of regular expressions, and sublinear average time for any regular expression, hence providing the first known algorithm to achieve this time complexity. The motivation behind these algorithms is the work done in the New Oxford English Dictionary Project. As a subproduct of the analysis of one of the algorithms, a technique to solve matricial recurrences is proposed. This technique can be applied to other problems, like fringe analysis and partial match queries in k-d tries. ---
wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (05/25/89)
DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES DATA STRUCTURES SEMINAR -Monday, May 29, 1989 Professor Mireille R`gnier, INRIA, France, will speak on "An Algebraic Analysis of the Knuth-Morris-Pratt Algorithm." TIME: 3:30 p.m. ROOM: DC 1304 ABSTRACT We present an average analysis of a basic string- searching algorithm: the Knuth-Morris-Pratt algorithm. We consider the number of text-pattern comparisons performed when searching a pattern p in a text t of length n. It is known to be O(n). We show that for a given pattern p and a random text t, this cost is asymptotically c subscript p n. Averaging over all possible patterns p yields a constant of linearity c. When the cardinality q of the alphabet is large, it is proven that c approximates 1 + 1 over q . An algebraic scheme is used, based on combinatorics on words and generating functions. First, the problem is reduced to a problem of word enumeration. Then, known results from combinatorics of words apply, which allow the computation of the associated generating functions.
wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (10/17/89)
DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES DATA STRUCTURES SEMINAR -Wednesday, October 18, 1989 Mr. Ron McFadyen, graduate student, Dept. of Computer Science, will speak on ``Partial Match Retrieval When Attributes Are Independently Specified.'' TIME: 10:30 a.m. ROOM: DC 1331 ABSTRACT We consider the cost of partial match queries in gray code and standard binary hash files when the probability of an attribute being specified is independent of other attributes. Query cost is modelled using cluster access and page transmissions. The cost function developed yields properties concerning bit assignments to attributes.
wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (01/18/90)
DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES DATA STRUCTURES SEMINAR -Wednesday, January 24, 1990 Darrell Raymond, Dept. of Computer Science, University of Waterloo, will speak on ``lector: An Interactive Formatter for Tagged Text.'' TIME: 1:30 p.m. ROOM: DC 3307 ABSTRACT lector is an X.11 program that provides provides highly interactive text formatting. Unlike many existing text previewers,lector accepts descriptively marked-up text, permits multiple views, and interacts well with other programs (including other invocations of lector). Appropriate selection of texts and styles enables lector to act as text previewer, database browser, code prettyprinter, or menu utility. lector's design involves an interesting set of trade-offs in an attempt to maximize efficiency, simplicity, and generality, demonstrating the utility of isolating text display in a single tool. January 18, 1990