2813562
Context-Based Morphological Disambiguation with Random Fields
Finite-state approaches have been highly successful at describing the morphological processes of many languages. Such approaches have largely focused on modeling the phone- or character-level processes that generate candidate lexical types, rather than tokens in context. For the full analysis of words in context, disambiguation is also required (Hakkani-Tur et al., 2000; Hajic et al., 2001). In this paper, we apply a novel source-channel model to the problem of morphological disambiguation (segmentation into morphemes, lemmatization, and POS tagging) for concatenative, templatic, and inflectional languages. The channel model exploits an existing morphological dictionary, constraining each word's analysis to be linguistically valid. The source model is a factored, conditionally-estimated random field (Lafferty et al., 2001) that learns to disambiguate the full sentence by modeling local contexts. Compared with baseline state-of-the-art methods, our method achieves statistically significant error rate reductions on Korean, Arabic, and Czech, for various training set sizes and accuracy measures.
11953962
Detecting events with date and place information in unstructured text
Digital libraries of historical documents provide a wealth of information about past events, often in unstructured form. Once dates and place names are identified and disambiguated, using methods that can differ by genre, we examine collocations to detect events. Collocations can be ranked by several measures, which vary in effectiveness according to type of events, but the log-likelihood measure (-2 log λ) offers a reasonable balance between frequently and infrequently mentioned events and between larger and smaller spatial and temporal ranges. Significant date-place collocations can be displayed on timelines and maps as an interface to digital libraries. More detailed displays can highlight key names and phrases associated with a given event.
1432381
Detecting and Browsing Events in Unstructured text
Previews and overviews of large, heterogeneous information resources help users comprehend the scope of collections and focus on particular subsets of interest. For narrative documents, questions of "what happened? where? and when?" are natural points of entry. Building on our earlier work at the Perseus Project with detecting terms, place names, and dates, we have exploited co-occurrences of dates and place names to detect and describe likely events in document collections. We compare statistical measures for determining the relative significance of various events. We have built interfaces that help users preview likely regions of interest for a given range of space and time by plotting the distribution and relevance of various collocations. Users can also control the amount of collocation information in each view. Once particular collocations are selected, the system can identify key phrases associated with each possible event to organize browsing of the documents themselves.
2964234
Random Trees and the Analysis of Branch and Bound Procedures
Branch and bound procedures are the most efficient known means for solving many NP-hard problems A special class of branch and bound procedures called relaxation-gutded procedures ig presented. While for some branch and bound procedures a worst-case complexity bound is known, the average case complexity is usually unknown, despite the fact that it may g~ve more useful information about the performance of the algorithm. A random process which generates labeled trees is introduced as a model of the kind of trees that a relaxatlon-gutded procedure generates over random instances of a problem Results concerning the expected time and space complexity of searching these random trees are derived with respect to several search strategies. The best-bound search strategy is shown to be optimal in both time and space. These results are illustrated by data from random traveling salesman instances Evidence ~s presented that the asymmetric traveling salesman problem can be solved exactly in time O(n31n(n)) on the average. Categories and Subject Descnptors: F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumencal Algorithms and Problems, G.2.1 [Discrete Mathematics]: Combinatorics; G.I.6 [Numerical Analysis]. OpUmlzatlon General Terms: Algorithms, Theory Addlttonal
7140389
Overcoming Ontology Mismatches in Transactions with Self-Describing Service Agents
One vision of the "Semantic Web" of the future is that software agents will interact with each other using formal metadata that reveal their interfaces. We examine one plausible paradigm, where agents provide service descriptions that tell how they can be used to accomplish other agents' goals. From the point of view of these other agents, the problem of deciphering a service description is quite similar to the standard AI planning problem, with some interesting twists. Two such twists are the possibility of having to reconcile contradictory ontologies -- or conceptual frameworks -- used by the agent, and having to rearrange the data structures of a message-sending agent so they match the expectations of the recipient. We argue that the former problem requires human intervention and maintenance, but that the latter can be fully automated.
44972038
Project CALC: Calculus as a Laboratory Course
Calculus is the study of change. The concepts of calculus enable us to model processes that change and to describe properties of these processes that remain constant in the midst of change. Now change has come to the learning of calculus -change driven by the need to respond to the revolution in technology and fueled by funds from the United States National Science Foundation. What should be changed? How and how fast? What should remain constant? In this paper we describe one answer to these questions: Project CALC, a new calculus course developed at Duke University. The key features of our approach are real-world problems, hands-on activities, discovery learning, writing and revision of writing, teamwork, and intelligent use of available tools.
5147691
Derived Preconditions and Their Use in Program Synthesis
In this paper we pose and begin to explore a deductive problem more general than that of finding a proof that a given goal formula logically follows from a given set of hypotheses. The problem is most simply stated in the propositional calculus: given a goal A and hypothesis H we wish to find a formula P, called a precondition, such that A logically follows from P ∧ H. A precondition provides any additional conditions under which A can be shown to follow from H. A slightly more complex definition of preconditions in a first-order theory is given and used throughout the paper. A formal system based on natural deduction is presented in which preconditions can be derived. A number of examples are then given which show how derived preconditions are used in a program synthesis method we are developing. These uses include theorem proving, formula simplification, simple code generation, the completion of partial specifications for a subalgorithm, and other tasks of a deductive nature.
18928754
An improved algorithm to determine lower bounds for the fixed spectrum frequency assignment problem
Frequencies have to be assigned to transmitters whenever a radio network is established or modified. This is ideally done is a way which minimises interference in the network. Lower bounds are necessary to establish the effectiveness of the heuristic algorithms used for this task and to assess the quality of the assignments obtained. 
 
In the fixed spectrum frequency assignment problem the available frequencies are known in advance. The constraints are often binary constraints, specifying the necessary frequency separation between given pairs of transmitters. There may be penalties (or weights) associated with the violation of each constraint; it is then either necessary to minimise the number of constraints violated or, increasingly often, to minimise the sum of the weights associated with violated constraints. 
 
A technique for generating lower bounds for these quantities is presented. This is an evolution of a technique which has recently appeared in the literature. It produces better quality bounds, is in general significantly faster and allows larger problems to be handled.