Ismail Hakki Toroslu

An architecture for workflow scheduling under resource allocation constraints

Research on specification and scheduling of workflows has concentrated on temporal and causality constraints, which specify existence and order dependencies among tasks. However, another set of constraints that specify resource allocation is also equally important. The resources in a workflow environment are agents such as person, machine, software, etc. that execute the task. Execution of a task has a cost and this may vary depending on the resources allocated in order to execute that task. Resource allocation constraints define restrictions on how to allocate resources, and scheduling under resource allocation constraints provide proper resource allocation to tasks. In this work, we provide an architecture to specify and to schedule workflows under resource allocation constraints as well as under the temporal and causality constraints. A specification language with the ability to express resources and resource allocation constraints and a scheduler module that contains a constraint solver in order to find correct resource assignments are core and novel parts of this architecture.

A logical framework for scheduling workflows under resource allocation constraints

A workflow consists of a collection of coordinated tasks designed to carry out a well-defined complex process, such as catalog ordering, trip planning, or a business process in an enterprise. Scheduling of workflows is a problem of finding a correct execution sequence for the workflow tasks, i.e., execution that obeys the constraints that embody the business logic of the workflow. Research on workflow scheduling has largely concentrated on temporal constraints, which specify correct ordering of tasks. Another important class of constraints -- those that arise from resource allocation -- has received relatively little attention in workflow modeling. Since typically resources are not limitless and cannot be shared, scheduling of a workflow execution involves decisions as to which resources to use and when. In this work, we present a framework for workflows whose correctness is given by a set of resource allocation constraints and develop techniques for scheduling such systems. Our framework integrates Concurrent Transaction Logic (CTR) with constraint logic programming (CLP), yielding a new logical formalism, which we call Concurrent Constraint Transaction Logic, or CCTR.

Genetic algorithm for the personnel assignment problem with multiple objectives

The assignment problem is a well-known graph optimization problem defined on weighted-bipartite graphs. The objective of the standard assignment problem is to maximize the summation of the weights of the matched edges of the bipartite graph. In the standard assignment problem, any node in one partition can be matched with any node in the other partition without any restriction. In this paper, variations of the standard assignment problem are defined with matching constraints by introducing structures in the partitions of the bipartite graph, and by defining constraints on these structures. According to the first constraint, the matching between the two partitions should respect the hierarchical-ordering constraints defined by forest and level graph structures produced by using the nodes of the two partitions respectively. In order to define the second constraint, the nodes of the partitions of the bipartite graph are distributed into mutually exclusive sets. The set-restriction constraint enforces the rule that in one of the partitions all the elements of each set should be matched with the elements of a set in the other partition. Even with one of these constraints the assignment problem becomes an NP-hard problem. Therefore, the extended assignment problem with both the hierarchical-ordering and set-restriction constraints becomes an NP-hard multi-objective optimization problem with three conflicting objectives; namely, minimizing the numbers of hierarchical-ordering and set-restriction violations, and maximizing the summation of the weights of the edges of the matching. Genetic algorithms are proven to be very successful for NP-hard multi-objective optimization problems. In this paper, we also propose genetic algorithm solutions for different versions of the assignment problem with multiple objectives based on hierarchical and set constraints, and we empirically show the performance of these solutions.

Genetic Algorithm for the Multiple-Query Optimization Problem

Producing answers to a set of queries with common tasks efficiently is known as the multiple-query optimization (MQO) problem. Each query can have several alternative evaluation plans, each with a different set of tasks. Therefore, the goal of MQO is to choose the right set of plans for queries which minimizes the total execution time by performing common tasks only once. Since MQO is an NP-hard problem, several, mostly heuristics based, solutions have been proposed for solving it. To the best of our knowledge, this correspondence is the first attempt to solve MQO using an evolutionary technique, genetic algorithms

Incremental assignment problem

In this paper we introduce the incremental assignment problem. In this problem, a new pair of vertices and their incident edges are added to a weighted bipartite graph whose maximum-weighted matching is already known, and the maximum-weighted matching of the extended graph is sought. We propose an O(|V|^2) algorithm for the problem.

Concept discovery on relational databases: New techniques for search space pruning and rule quality improvement

Multi-relational data mining has become popular due to the limitations of propositional problem definition in structured domains and the tendency of storing data in relational databases. Several relational knowledge discovery systems have been developed employing various search strategies, heuristics, language pattern limitations and hypothesis evaluation criteria, in order to cope with intractably large search space and to be able to generate high-quality patterns. In this work, we introduce an ILP-based concept discovery framework named Concept Rule Induction System (CRIS) which includes new approaches for search space pruning and new features, such as defining aggregate predicates and handling numeric attributes, for rule quality improvement. In CRIS, all target instances are considered together, which leads to construction of more descriptive rules for the concept. This property also makes it possible to use aggregate predicates more accurately in concept rule construction. Moreover, it facilitates construction of transitive rules. A set of experiments is conducted in order to evaluate the performance of proposed method in terms of accuracy and coverage.

Sentiment Analysis of Turkish Political News

In this paper, sentiment classification techniques are incorporated into the domain of political news from columns in different Turkish news sites. We compared four supervised machine learning algorithms of Naïve Bayes, Maximum Entropy, SVM and the character based N-Gram Language Model for sentiment classification of Turkish political columns. We also discussed in detail the problem of sentiment classification in the political news domain. We observe from empirical findings that the Maximum Entropy and N-Gram Language Model outperformed the SVM and Naïve Bayes. Using different features, all the approaches reached accuracies of 65% to 77%.

ILP-based concept discovery in multi-relational data mining

Multi-relational data mining has become popular due to the limitations of propositional problem definition in structured domains and the tendency of storing data in relational databases. Several relational knowledge discovery systems have been developed employing various search strategies, heuristics, language pattern limitations and hypothesis evaluation criteria, in order to cope with intractably large search space and to be able to generate high-quality patterns. In this work, an ILP-based concept discovery method, namely Confidence-based Concept Discovery (C^2D), is described in which strong declarative biases and user-defined specifications are relaxed. Moreover, this new method directly works on relational databases. In addition to this, a new confidence-based pruning is used in this technique. We also describe how to define and use aggregate predicates as background knowledge in the proposed method. In order to use aggregate predicates, we show how to handle numerical attributes by using comparison operators on them. Finally, we analyze the effect of incorporating unrelated facts for generating transitive rules on the proposed method. A set of experiments are conducted on real-world problems to test the performance of the proposed method.

A Dynamic Modularity Based Community Detection Algorithm for Large-scale Networks: DSLM

In this work, a new fast dynamic community detection algorithm for large scale networks is presented. Most of the previous community detection algorithms are designed for static networks. However, large scale social networks are dynamic and evolve frequently over time. To quickly detect communities in dynamic large scale networks, we proposed dynamic modularity optimizer framework (DMO) that is constructed by modifying well-known static modularity based community detection algorithm. The proposed framework is tested using several different datasets. According to our results, community detection algorithms in the proposed framework perform better than static algorithms when large scale dynamic networks are considered.

Discovering better navigation sequences for the session construction problem

In this paper, we propose a novel page view based session model and session construction method to address the Web Usage Mining (WUM) problem. Unlike the simple session models, where sessions are sequences of web pages requested from the server (or served from a browser/proxy cache) and viewed in the browser (which may not guarantee a direct relationship between subsequent web pages in the session), we define a more realistic session model in which a session is a set of paths traversed in the web graph that corresponds to a user navigation performed by following links on web pages. We define the session construction process from raw server logs as a new graph problem and present a novel algorithm, Smart-SRA (Smart Session Reconstruction Algorithm), to solve this problem efficiently. An experimental evaluation based on data collected from real web access scenarios showed that Smart-SRA produces more accurate user sessions than the session construction methods found in the literature.