Esko Nuutila

On finding the strongly connected components in a directed graph

Abstract We present two improved versions of Tarjans algorithm for the detection of strongly connected components in a directed graph. Our new algorithms handle sparse graphs and graphs with many trivial components (containing only one node) more economically than Tarjans original algorithm. As an application we present an efficient transitive closure algorithm.

An efficient transitive closure algorithm for cyclic digraphs

Abstract We present a new transitive closure algorithm that is based on strong component detection. The new algorithm is more efficient than the previous transitive closure algorithms that are based on strong components detection, since it does not generate unnecessary partial successor sets and scans the input graph only once.

XC- A language for embedded rule based systems

We report on experiences in the design of the programming language XC. It is an extension of C++ and combines abstract data types with rule based programming. Our design decisions are validated by three application prototypes and by benchmarking XC and OPS83. The experiences raise some critique on the RETE algorithm and on C++ as a host language. However, most of the results are also applicable to other host languages that support data abstraction. XC has been designed specifically to be used in embedded real-time expert systems.

Transitive closure algorithm MEMTC and its performance analysis

In this paper, we present a new algorithm for computing the full transitive closure designed for operation in layered memories. The algorithm is based on strongly connected component detection and on a very compact representation of data. We analyze the average-case performance of the algorithm experimentally in an environment where two layers of memory of different speed are used. In our analysis, we use trace-based simulation of memory operations.

Supporting testing of specifications and implementations

Abstract A system is presented that can generate tests from the specification of a computer program. It requires some information from the user to avoid combinatorial explosion. The tests are used to test both the specification and the implementation. Two methods are presented for transforming the tests to a form suitable for testing the implementation. An experiment indicates that the test case generation methods are fairly effective.

XE design rationale: Clu revisited

XE is a programming language designed and implemented at the Helsinki University of Technology by the ExBed project. The design of XE is based on the CLU programming language. This paper discusses differences between the two languages and the design decisions of XE.