Guoyong Cai

Using ASP for knowledge management with user authorization

Unlike conventional rule based knowledge bases (KBs) that support monotonic reasoning, a key correctness issue, i.e. the correctness of a sub-KB with respect to the full KB, arises when using a KB represented by non-monotonic reasoning languages such as Answer Set Programming (ASP). Since a user may have rights to access only a subset of a KB, the non-monotonic nature of ASP may cause the occurrence of consequences, which are erroneous in the sense that the consequences are not reasonable in the full KB. This paper proposes an approach dealing with the problem. The main idea is to let the usage of Closed World Assumptions (CWAs) for literals in a KB satisfy certain constraints. Two kinds of access right propositions are created, rule retrieval right propositions to control the access to rules, and CWA right propositions to control the usage of CWAs for literals. Based on these right propositions, this paper first defines an algorithm for translating an original KB into a KB tagged by right propositions, and then discusses the right dependency in a KB and proposes methods for checking and obtaining a set of rights that is closed under a set of dependency rules. Finally, several results on the correctness of a set of rights in a KB are presented, which serve as guidelines for the correct use of a KB. As an example, a KB of illness-related financial support for teachers of a university is presented to illustrate the application of our approach.

Symbolic ZBDD Representations for Mechanical Assembly Sequences

The representations of assembly knowledge and assembly sequences are crucial in assembly planning, where the size of parts involved is a significant and often prohibitive difficulty. Zero-suppressed binary decision diagram (ZBDD) is an efficient form to represent and manipulate the sets of combination, and appears to give improved results for large-scale combinatorial optimization problems. In this paper, liaison graphs, translation functions, assembly states and assembly tasks are represented as sets of combinations, and the symbolic ZBDD representation of assembly sequences is proposed. An example is given to show the feasibility of the ZBDD-based representation scheme.

Temporal dynamics in social trust prediction

Inferring unknown social trust relations attracts increasing attention in recent years. However, social trust, as a social concept, is intrinsically dynamic, and exploiting temporal dynamics provides challenges and opportunities for social trust prediction. In this paper, we investigate social trust prediction by exploiting temporal dynamics. In particular, we model the dynamics of user preferences in two principled ways. The first one focuses on temporal weight; the second one targets temporal smoothness. By incorporating these two types of temporal dynamics into traditional matrix factorization based social trust prediction model, two extended social trust prediction models are proposed and the corresponding algorithms to solve the models are designed too. We conduct experiments on a real-world dataset and the results demonstrate the effectiveness of our proposed new models. Further experiments are also conducted to understand the importance of temporal dynamics in social trust prediction.

Automatic Construction of Complete Abstraction by Abstract Interpretation

Abstraction plays a fundamental role in combating state-space explosion in model checking. Firstly, we study how to abstract models of mu-calculus and derive abstractions that are sound, and apply them to abstracting Kripke structures. However, a lack of completeness in the abstract interpretation leads to spurious counterexamples in the abstract model checking. In order to eliminate spurious counterexamples, the paper describes a method for minimally making abstract interpretations complete, and this refined complete abstract domain always exists.

A novel test case generation method for prolog programs based on call patterns semantics

A natural way to generate test cases for a Prolog program is to view the call patterns of the procedures in the program as an implicit representation of the control flow graph (CFG) of the program. This paper explores the idea by proposing a call patterns-based test case generation method, where a set of call patterns or computed answers is used to describe the paths in a CFG. With a constraint-based call patterns semantics, this method is formalized. Through the use of a proper constraints solver, we can generate test cases automatically from the sets of constraints. This method can be based on any approximation of the call patterns semantics. So compared with traditional CFG-based test case generation, the method is more flexible and can be easily adapted to meet the requirements of a tester expressed by the approximation of the call patterns semantics we use.

Formula-Dependent Abstraction for CTL Model Checking

We present a state abstraction that is defined with respect to a given CTL formula. Since it does not attempt to preserve all ACTL formula, like simulation does, we can expect to compute coarser abstraction. Specifically, the abstraction is used to reduce the size of each Kripke structure, so that their product will be smaller. When the abstraction is too coarse, we show how refinement can be applied to produce a more precise abstract model. We also extend the notion of formula-dependent abstraction to Kripke structure with fairness, and define the coarsest abstraction that preserves the given CTL formula interpreted with respect to the fair paths. The method is exact and fully automatic, and handles full CTL.

Test frame updating in CPM testing of Prolog programs

Category Partition Method (CPM) is a general approach to specification-based program testing, where test frame reduction and refinement are two important issues. Test frame reduction is necessary since too many test frames may be produced, and test frame refinement is important since during CPM testing new information about test frame generation may be achieved and considered incrementally. Besides the information provided by testers or users, implementation related knowledge offers alternative information for reducing and refining CPM test frames. This paper explores the idea by proposing a call patterns semantics based test frame updating method for Prolog programs, in which a call patterns analysis is used to collect information about the way in which procedures are used in a program. The updated test frames will be represented as constraints. The effect of our test frame updating is two-fold. On one hand, it removes “uncared” data from the original set of test frames; on the other hand, it refines the test frames to which we should pay more attention. The first effect makes the input domain on which a procedure must be tested a subset of the procedure’s input domain, and the latter makes testers stand more chance to find out the faults that are more likely to show their presence in the use of the program under consideration. Our test frame updating method preserves the effectiveness of CPM testing with respect to the detection of faults we care. The test case generation from the updated set of test frames is also discussed. In order to show the applicability of our method an approximation call patterns semantics is proposed, and the test frame updating on the semantics is illustrated by an example.

Designing prolog semantics for a class of observables

Prolog is a well-known logic programming language. The information on the correct partial answers (cpa) and correct call patterns (ccp) of goals is useful for static analysis of Prolog programs. Decorated tree (DT) semantics is a goal-independent denotational semantics for Prolog that has been shown to be promising in Prolog program analysis. We extend the work in [7] and propose a two-step method for achieving cpa or ccp semantics from DT semantics. This paper is mainly concerned with the design of semantic domains.

On the new application of call patterns to CPM testing of prolog programs

Information on call patterns is known to be useful for analysis and optimization of Prolog programs. Several call patterns semantics exists for Prolog or for the subset of Prolog. In this paper we propose a method to apply the call patterns semantics to CPM testing of Prolog programs. The method can be viewed as an attempt to improve the testing of Prolog programs by the result of program analysis. By analyzing the way in which procedures are used in a program, we can reduce the number of test frames and therefore the number of test cases generated in CPM testing of a procedure.

ALCIR + Reasoning for Semantic Web Services Composition

Description logic (DL) ALCI R + is a very expressive knowledge representation and reasoning language formed by adding transitive roles and inverse roles to the basic DL ALC. Transitive roles in ALCI R + are appropriate for describing accessibility relationship between services, while the relationship is encoded as a ServiceProcess in DAML-S as an external understanding. The transitive closure of the special transitive role which represents accessibility relationship between the first and final services can be used to find an execution sequence of the composite service. We have presented a procedure for computing it. Existing standards DAML-S and convenient transformation from ServiceProcess in DAML-S to transitive roles in ALCI R + helps to make our method simple and viable.