Pierre Kelsen

A Lightweight Approach for Defining the Formal Semantics of a Modeling Language

To define the formal semantics of a modeling language, one normally starts from the abstract syntax and then defines the static semantics and dynamic semantics. Having a formal semantics is important for reasoning about the language but also for building tools for the language. In this paper we propose a novel approach for this task based on the Alloy language. With the help of a concrete example language, we contrast this approach with traditional methods based on formal languages, type checking, meta-modeling and operational semantics. Although both Alloy and traditional techniques yield a formal semantics of the language, the Alloy-based approach has two key advantages: a uniform notation, and immediate automatic analyzability using the Alloy analyzer. Together with the simplicity of Alloy, our approach offers the prospect of making formal definitions easier, hopefully paving the way for a wider adoption of formal techniques in the definition of modeling languages.

On the parallel complexity of computing a maximal independent set in a hypergraph

A maximal independent set in a hypergraph is a subset of vertices that is maximal with respect to the property of not containing any edge of the hypergraph. We show that an algorithm proposed by Beame and Luby is in randomized NC for hypergraphs in which the maximum edge size is bounded by a constant. To prove this, we bound the upper tail of sums of dependent random variables defined on the edges of a hypergraph. These bounds may be viewed as extensions of bounds on the tail of the binomial distribution. We derandomize this algorithm to obtain the first sublinear time deterministic algorithm for hypergraphs with edges of size O(1). The algorithm exhibits the following time-processor tradeoff: it can be made to run in time O(<italic>n</italic><supscrpt>ε</supscrpt>) with <italic>n</italic><supscrpt>O(1/ε)</supscrpt> processors for a hypergraph on <italic>n</italic> vertices, for any ε ≥ 2<supscrpt>d+1</supscrpt>• (log log <italic>n</italic>)/(log <italic>n</italic>); here <italic>d</italic> = O(1) denotes the maximum size of an edge in H. In particular, for any constant ε > O, we have an algorithm running in time O(<italic>n</italic><supscrpt>ε</supscrpt>) on a polynomial number of processors, and we have an algorithm running in time (log <italic>n</italic>)<supscrpt>O(1)</supscrpt> on <italic>n</italic><supscrpt>O(log <italic>n</italic>/log log <italic>n</italic>)</supscrpt> processors.

Models within models: taming model complexity using the sub-model lattice

Model-driven software development aims at easing the process of software development by using models as primary artifacts. Although less complex than the real systems they are based on, models tend to be complex nevertheless, thus making the task of comprehending them non-trivial in many cases. In this paper we propose a technique for model comprehension based on decomposing models into sub-models that conform to the same metamodel as the original model. The main contributions of this paper are: a mathematical description of the structure of these sub-models as a lattice, a linear-time algorithm for constructing this decomposition and finally an application of our decomposition technique to model comprehension.

CoReL: Policy-Based and Model-Driven Regulatory Compliance Management

Regulatory compliance management is now widely recognized as one of the main challenges still to be efficiently dealt with in information systems. In the discipline of business process management in particular, compliance is considered as an important driver of the efficiency, reliability and market value of companies. It consists of ensuring that enterprise systems behave according to some guidance provided in the form of regulations. This paper gives a definition of the research problem of regulatory compliance. We show why we expect a formal policy-based and model-driven approach to provide significant advantages in allowing enterprises to flexibly manage decision-making related to regulatory compliance. For this purpose, we contribute CoReL, a domain-specific modeling language for representing compliance requirements that has a graphical concrete syntax. Informal semantics of CoReL are introduced and its use is illustrated on an example. CoReL allows to leverage business process compliance modeling and checking, enhancing it with regard to, among other dimensions, user-friendliness, genericity, and traceability.

A modular model composition technique

Model composition is a technique for building bigger models from smaller models, thus allowing system designers to control the complexity of a model-driven design process. However many current model composition techniques are themselves complex in the sense that they merge the internal elements of the participating models in non-trivial ways. In this paper we apply some of the ideas from modular programming to reduce the complexity of model compositions. Indeed we propose a model composition technique with a modular flavor that treats the participating models as black boxes. Our technique has several desirable features: it is simple, it does not require a separate language for expressing the composition, and the understanding of the resulting composed model is made easier by the modular nature of the model composition.

An efficient parallel algorithm for computing a maximal independent set in a hypergraph of dimension 3

The paper considers the problem of computing a maximal independent set in a hypergraph (see \cite{BL} and \cite{KR}). We present an efficient deterministic NC algorithm for finding a maximal independent set in a hypergraph of dimension

Modular Design by Contract Visually and Formally Using VCL

3

Computing Minimal Spanning Subgraphs in Linear Time

: the algorithm runs in time

Using VCL as an aspect-oriented approach to requirements modelling

O(\log^4 n)

F-Alloy: An Alloy Based Model Transformation Language

time on