August 2010

Document Type


Degree Name



Dept. of Science & Engineering


Oregon Health & Science University


Pipeline systems, in which data is processed in stages with the output of one stage providing input to the next, are ubiquitous in the field of natural language processing (NLP) as well as many other research areas. The popularity of the pipeline system architecture is due to the utility of pipelines in reducing search complexity, increasing efficiency, and re-using system components. Despite the widespread use of pipelines, there has been little effort toward understanding their functionality and establishing a set of best practices for defining and improving these systems. Improvement techniques are usually discovered in an ad-hoc manner, difficult to generalize for implementation in other systems, and lacking in thorough systematic evaluation of the effects of the technique on the pipeline system. This dissertation identifies and generalizes shared aspects of pipeline systems across several different application areas, including parsing, speech recognition, machine translation, and image classification. A formal framework of pipeline systems is defined, based on these shared aspects, and the argument is made that pipeline improvement techniques derived from this framework will be more easily generalized for application to other pipeline systems. A systematic and thorough examination of the characteristics of constraints used within several different pipelines is conducted to determine the effects of these characteristics on pipeline performance. This dissertation will define quantitative metrics of constraint characteristics including diversity, regularity, density, and peakedness. Results will demonstrate that 1) current metrics of constraint quality (typically intrinsic one-best and oracle evaluations) are insufficient predictors of pipeline performance, and 2) several quantitative characteristics of the constraints can be systematically altered to a affect pipeline performance. The framework, general improvement techniques, and quantitative measures of the search space as provided by this dissertation, are important steps towards improving the comparison, analysis, and understanding of pipeline systems.




Div. of Biomedical Computer Science


School of Medicine



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