K. Narayan Kumar

Learn More
Message Sequence Charts (MSCs) are an attractive visual formalism widely used to capture system requirements during the early design stages in domains such as telecommunication software. It is fruitful to have mechanisms for specifying and reasoning about collections of MSCs so that errors can be detected even at the requirements level. We propose,(More)
Message Sequence Charts (MSCs) are an attractive visual formalism widely used to capture system requirements during the early design stages in domains such as telecommunication software. A standard method to describe multiple communication scenarios is to use message sequence graphs (MSGs). A message sequence graph allows the protocol designer to write a(More)
Message Sequence Charts (MSCs) are an attractive visual formalism used during the early stages of design in domains such as telecommunication software. A popular mechanism for generating a collection of MSCs is a Hierarchical Message Sequence Chart (HMSC). However, not all HMSCs describe collections of MSCs that can be “realized” as a finite-state device.(More)
We propose a model of distributed timed systems where each component is a timed automaton with a set of local clocks that evolve at a rate independent of the clocks of the other components. A clock can be read by any component in the system, but it can only be reset by the automaton it belongs to. There are two natural semantics for such systems. The(More)
Given a logic program <i>P</i>, an unfold/fold program transformation system derives a sequence of programs <i>P</i> = <i>P</i><sub>0</sub>, <i>P</i><sub>1</sub>, &#8230;, <i>P</i><sub><i>n</i></sub>, such that <i>P</i><sub><i>i</i>+1</sub> is derived from <i>P</i><sub><i>i</i></sub> by application of either an unfolding or a folding step. Unfold/fold(More)
We define a new notation called netcharts for describing sets of message sequence chart scenarios (MSCs). Netcharts correspond to a distributed version of High-level Message Sequence Charts (HMSCs). Netcharts improve on HMSCs in two respects. (i) Netcharts admit a natural and direct translation into communicating finite-state machines, unlike HMSCs, for(More)
We consider message sequence charts enriched with timing constraints between pairs of events. As in the untimed setting, an infinite family of time-constrained message sequence charts (TC-MSCs) is generated using an HMSC—a finite-state automaton whose nodes are labelled by TC-MSCs. A timed MSC is an MSC in which each event is assigned an explicit(More)
We formally characterize alternating fixed points of boolean equation systems as models of (propositional) normal logic programs. To precisely capture this relationship, we introduce the notion of a preferred stable model of a logic program, and define a mapping that associates a normal logic program with a boolean equation system such that the solution to(More)
Multi-threaded programs with recursion are naturally modeled as multi-pushdown systems. The behaviors are represented as multiply nested words (MNWs), which are words enriched with additional binary relations for each stack matching a push operation with the corresponding pop operation. Any MNW can be decomposed by two basic and natural operations: shuffle(More)