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33
Dynamic Typing
 In Proc. Fourth European Symp. Programming (ESOP’92
, 1992
"... We present an extension of a statically typed language with a special type Dynamic and explicit type tagging and checking operations (coercions). Programs in runtime typed languages are viewed as incomplete programs that are to be completed to welltyped programs by explicitly inserting coercions i ..."
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Cited by 36 (3 self)
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We present an extension of a statically typed language with a special type Dynamic and explicit type tagging and checking operations (coercions). Programs in runtime typed languages are viewed as incomplete programs that are to be completed to welltyped programs by explicitly inserting coercions into them. Such completions are generally not unique. If the meaning of an incomplete program is to be the meaning of any of its completions and if it is too be unambiguous it is necessary that all its completions are coherent (semantically equivalent). We characterize with an equational theory the properties a semantics must satisfy to be coherent. Since “naive ” coercion evaluation does not satisfy all of the coherence equations we exclude certain “unsafe ” completions from consideration that can cause avoidable type errors at runtime. Various classes of completions may be used, parameterized by whether or not coercions may only occur at data creation and data use points in a program and whether only primitive coercions or also induced coercions. For each of these classes any term has a minimal completion that is optimal in the sense that it contains no coercions that could be avoided by a another coercion in the same class. In particular, minimal completions contain no coercions at all whenever the program is statically typable. If only primitive type operations are admitted we show that minimal completions can be computed in almostlinear time. If induced coercions are also allowed the minimal completion can be computed in time O(nm) where n is the size of the program and m is the size of the value flow graph of the program, which may be of size O(n 2), but is typically rather sparse. Finally, we sketch how this explicit dynamic typing discipline can be extended to letpolymorphism by parameterization with respect to coercions. The resulting language framework leads to a seamless integration of statically typed and dynamically typed languages by relying on type inference for programs that have no type information and no explicit coercions whatsoever. 1
Optimal UnionFind in Constraint Handling Rules
 THEORY AND PRACTICE OF LOGIC PROGRAMMING
, 2006
"... Constraint Handling Rules (CHR) is a committedchoice rulebased language that was originally intended for writing constraint solvers. In this paper we show that it is also possible to write the classic unionfind algorithm and variants in CHR. The programs neither compromise in declarativeness nor ..."
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Cited by 34 (25 self)
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Constraint Handling Rules (CHR) is a committedchoice rulebased language that was originally intended for writing constraint solvers. In this paper we show that it is also possible to write the classic unionfind algorithm and variants in CHR. The programs neither compromise in declarativeness nor e#ciency. We study the time complexity of our programs: they match the almostlinear complexity of the best known imperative implementations. This fact is illustrated with experimental results.
Parallelizing unionfind in Constraint Handling Rules using confluence analysis
 LOGIC PROGRAMMING: 21ST INTERNATIONAL CONFERENCE, ICLP 2005, VOLUME 3668 OF LECTURE NOTES IN COMPUTER SCIENCE
, 2005
"... Constraint Handling Rules is a logical concurrent committedchoice rulebased language. Recently it was shown that the classical unionfind algorithm can be implemented in CHR with optimal time complexity. Here we investigate if a parallel implementation of this algorithm is also possible in CHR. The ..."
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Cited by 29 (15 self)
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Constraint Handling Rules is a logical concurrent committedchoice rulebased language. Recently it was shown that the classical unionfind algorithm can be implemented in CHR with optimal time complexity. Here we investigate if a parallel implementation of this algorithm is also possible in CHR. The problem is hard for several reasons: Up to now, no parallel computation model for CHR was defined. Tarjan’s optimal unionfind is known to be hard to parallelize. The parallel code should be as close as possible to the sequential one. It turns out that confluence analysis of the sequential implementation gives almost all the information needed to parallelize the unionfind algorithm under a rather general parallel computation model for CHR.
K.U.Leuven JCHR: a userfriendly, flexible and efficient CHR system for Java
 IN PROC. 2ND WORKSHOP ON CONSTRAINT HANDLING RULES (CHR’05
, 2005
"... A new integration of Constraint Handling Rules (CHR) and Java is presented: the K.U.Leuven JCHR system. It was designed with three aims in mind: userfriendliness, flexibility and efficiency. Userfriendliness is achieved by providing a highlevel syntax that feels familiar to both Java programmers ..."
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Cited by 19 (14 self)
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A new integration of Constraint Handling Rules (CHR) and Java is presented: the K.U.Leuven JCHR system. It was designed with three aims in mind: userfriendliness, flexibility and efficiency. Userfriendliness is achieved by providing a highlevel syntax that feels familiar to both Java programmers and users of other CHR embeddings, and by full compliance to the refined operational semantics. Flexibility is the result of a well thoughtout design, allowing e.g. an easy integration of builtin constraint solvers and variable types. Efficiency is achieved through an optimized compilation to Java and the use of a very efficient constraint store. The design of the K.U.Leuven JCHR system is presented, its implementation discussed and its performance is compared with other CHR systems embedded in Java and Prolog.
HitList Worm Detection and Bot Identification in Large Networks Using Protocol Graphs
 Recent Advances in Intrusion Detection (RAID), 10th International Symposium, RAID 2007
, 2007
"... Abstract. We present a novel method for detecting hitlist worms using protocol graphs. In a protocol graph, a vertex represents a single IP address, and an edge represents communications between those addresses using a specific protocol (e.g., HTTP). We show that the protocol graphs of four diverse ..."
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Cited by 18 (6 self)
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Abstract. We present a novel method for detecting hitlist worms using protocol graphs. In a protocol graph, a vertex represents a single IP address, and an edge represents communications between those addresses using a specific protocol (e.g., HTTP). We show that the protocol graphs of four diverse and representative protocols (HTTP, FTP, SMTP, and Oracle), as constructed from monitoring for fixed durations on a large intercontinental network, exhibit stable graph sizes and largest connected component sizes. Moreover, we demonstrate that worm propagations, even of a sophisticated hitlist variety in which the attacker has advance knowledge of his targets and always connects successfully, perturb these properties. We demonstrate that these properties can be monitored very efficiently even in very large networks, giving rise to a viable and novel approach for worm detection. We also demonstrate extensions by which the attacking hosts (bots) can be identified with high accuracy.
What is a "Pointer Machine"?
 Science of Computer Programming
, 1995
"... A "Pointer Machine" is many things. Authors who consider referring to this term are invited to read the following note first. 1 Introduction In a 1992 paper by Galil and the author we referred to a "pointer machine " model of computation. A subsequent survey of related literature has produced over ..."
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Cited by 16 (1 self)
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A "Pointer Machine" is many things. Authors who consider referring to this term are invited to read the following note first. 1 Introduction In a 1992 paper by Galil and the author we referred to a "pointer machine " model of computation. A subsequent survey of related literature has produced over twenty references to papers having to do with "pointer machines", naturally containing a large number of crossreferences. These papers address a range of subjects that range from the model considered in the above paper to some other ones which are barely comparable. The fact that such different notions have been discussed under the heading of "pointer machines" has produced the regrettable effect that cross references are sometimes found to be misleading. Clearly, it is easy for a reader who does not follow a paper carefully to misinterpret its claims when a term that is so illdefined is used. This note is an attempt to rectify the situation. We start with a survey of the different notions...
Spaceconstrained grambased indexing for efficient approximate string search (full version
, 2008
"... Abstract — Answering approximate queries on string collections is important in applications such as data cleaning, query relaxation, and spell checking, where inconsistencies and errors exist in user queries as well as data. Many existing algorithms use grambased invertedlist indexing structures t ..."
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Cited by 16 (3 self)
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Abstract — Answering approximate queries on string collections is important in applications such as data cleaning, query relaxation, and spell checking, where inconsistencies and errors exist in user queries as well as data. Many existing algorithms use grambased invertedlist indexing structures to answer approximate string queries. These indexing structures are “notoriously” large compared to the size of their original string collection. In this paper, we study how to reduce the size of such an indexing structure to a given amount of space, while retaining efficient query processing. We first study how to adopt existing invertedlist compression techniques to solve our problem. Then, we propose two novel approaches for achieving the goal: one is based on discarding gram lists, and one is based on combining correlated lists. They are both orthogonal to existing compression techniques, exploit a unique property of our setting, and offer new opportunities for improving query performance. For each approach we analyze its effect on query performance and develop algorithms for wisely choosing lists to discard or combine. Our extensive experiments on real data sets show that our approaches provide applications the flexibility in deciding the tradeoff between query performance and indexing size, and can outperform existing compression techniques. An interesting and surprising finding is that while we can reduce the index size significantly (up to 60 % reduction) with tolerable performance penalties, for 2040 % reductions we can even improve query performance compared to original indexes. I.
Analysing the CHR implementation of unionfind
"... www.informatik.uniulm.de/pm/mitarbeiter/fruehwirth/ Abstract. CHR (Constraint Handling Rules) is a committedchoice rulebased language that was originally intended for writing constraint solvers. Over time, CHR is used more and more as a generalpurpose programming language. In companion paper [12] ..."
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Cited by 11 (7 self)
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www.informatik.uniulm.de/pm/mitarbeiter/fruehwirth/ Abstract. CHR (Constraint Handling Rules) is a committedchoice rulebased language that was originally intended for writing constraint solvers. Over time, CHR is used more and more as a generalpurpose programming language. In companion paper [12] we show that it is possible to write the classic unionfind algorithm and variants in CHR with bestknown time complexity, which is believed impossible in Prolog. In this paper, using CHR analysis techniques, we study logical correctness and confluence of these programs. We observe the essential destructive update of the algorithm which makes it nonlogical. 1
Efficient Algorithms for the Domination Problems on Interval and CircularArc Graphs
 SIAM J. Comput
, 1998
"... Abstract. This paper first presents a unified approach to design efficient algorithms for the weighted domination problem and its three variants, i.e., the weighted independent, connected, and total domination problems, on interval graphs. Given an interval model with endpoints sorted, these algorit ..."
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Cited by 9 (1 self)
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Abstract. This paper first presents a unified approach to design efficient algorithms for the weighted domination problem and its three variants, i.e., the weighted independent, connected, and total domination problems, on interval graphs. Given an interval model with endpoints sorted, these algorithms run in time O(n) orO(n log log n) where n is the number of vertices. The results are then extended to solve the same problems on circulararc graphs in O(n + m) time where m is the number of edges of the input graph.
Anonymizing Moving Objects: How to Hide a MOB in a Crowd?
"... Moving object databases (MOD) have gained much interest in recent years due to the advances in mobile communications and positioning technologies. Study of MOD can reveal useful information (e.g., traffic patterns and congestion trends) that can be used in applications for the common benefit. In ord ..."
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Cited by 8 (2 self)
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Moving object databases (MOD) have gained much interest in recent years due to the advances in mobile communications and positioning technologies. Study of MOD can reveal useful information (e.g., traffic patterns and congestion trends) that can be used in applications for the common benefit. In order to mine and/or analyze the data, MOD must be published, which can pose a threat to the location privacy of a user. Indeed, based on prior knowledge of a user’s location at several time points, an attacker can potentially associate that user to a specific moving object (MOB) in the published database and learn her position information at other time points. In this paper, we study the problem of privacypreserving publishing of moving object database. Unlike in microdata, we argue that in MOD, there does not exist a fixed set of quasiidentifier (QID) attributes for all the MOBs. Consequently the anonymization groups of MOBs (i.e., the sets of other MOBs within which to hide) may not be disjoint. Thus, there may exist MOBs that can be identified explicitly by combining different anonymization groups. We illustrate the pitfalls of simple adaptations of classical kanonymity and develop a notion which we prove is robust against privacy attacks. We propose two approaches, namely extremeunion and symmetric anonymization, to build anonymization groups that provably satisfy our proposed kanonymity requirement, as well as yield low information loss. We ran an extensive set of experiments on large realworld and synthetic datasets of vehicular traffic. Our results demonstrate the effectiveness of our approach. 1.