This paper deals with the dynamics of hybrid systems under piecewise open-loop controls restricted by hard bounds. The system equations may be reset when crossing some prespecified domains (“the guards”) in the state space. Therefore the continuous dynamics which govern the motion between the guards are complemented by discrete transitions which govern the resets. A state space model for such s...

Software applications are inevitably concerned with data integrity, whether the data is stored in a database, files, or program memory. An integrity guard is code executed before a data update is performed. The guard returns “true” just if the update will preserve data integrity. The problem considered here is how integrity guards can be produced automatically from data integrity constraints. W...

We describe a new purely software-based, self-checking mechanism designed to prevent tampering of client programs in client/server-applications like online-games, peer-to-peer networks, or online auction systems. Our mechanism consists of randomly creating checksum algorithms at the server. The checksum algorithms are integrated into autonomous short-lived software code, called Mobile Guards, w...

We introduce the notion of a normal gallery, a gallery in which any configuration of guards that visually covers the walls necessarily covers the entire gallery. We show that any star gallery is normal and any gallery with at most two reflex corners is normal. A polynomial time algorithm is provided deciding if, for a given gallery and a finite set of positions within the gallery, there exists ...

In this paper we discuss a possibility to extend unimodular transformations to non-perfectly nested loops. The main idea behind this extension is to convert a non-perfectly nested loop into a perfectly nested one by moving code into to innermost loop and properly guarding it to avoid multiple execution. This form of the loop can be viewed as an intermediate form for the transformation. Having o...

The problem of searching for a mobile intruder in a polygonal region by a set of stationary guards, each carrying an orientable laser, is known in the literature as the Searchlight Scheduling Problem. A long-standing conjecture concerns the NP-hardness of deciding if a given polygon is searchable by a given set of guards. In this paper we introduce the more general problem of detecting an intru...