It is well-known that the size of an ordered binary decision diagram (OBDD) may depend crucially on the order in which the variables occur. In the paper, we describe an implementation of an outputefficient algorithm that transforms an OBDD P representing a Boolean function f with respect to one variable ordering π into an OBDD Q that represents f with respect to another variable ordering σ. The algorithm runs in average time O(¦P∥Q¦) and requires O(¦P¦+n¦Q¦) space. The importance of the algorithm is demonstrated by means of experimental results on basically two different applications. In one of them, the algorithm is used merely once. Such transformations are needed to test equivalence or to perform synthesis on OBDDs in which variables appear in different orders. The other application shows a way how to decrease the size of intermediate representations in the course of the construction of OBDDs from a given circuit. Here the algorithm is used dynamically, whenever the size of the manipulated OBDDs becomes too large.

The Electronic Colloquium on Computational Complexity (ECCC) is a digital library that specifically addresses the current problem of scientific publishing, more precisely, the problem of presenting suitably filtered work to other researchers, for the field of computational complexity. Developing the detailed concepts in discussions with a scientific board of researchers in this field, ECCC now fills the gap between author controlled electronic publication (preprint servers, very fast but lacking content filtering) and conventional journal or conference proceedings publication (currently taking months, if not over a year, from submission to publication). Additionally, like a real colloquium, ECCC supports ongoing discussions through the publication of comments to already published material. Further authors have the possibility to present improved versions of their publications while maintaining bibliographic consistency by version control. In this paper, we will first describe the situation ECCC is meant to remedy (Sections 1 and 2) and then detail the setup with respect to organization (3.1), basic functionality (3.2 through 3.4), cooperation with other services (3.5) and plans for the future (3.6).

The idea of data transfer by physically severed connections has been applied in a simple realization of the Lock-Keeper technology, the SingleGate Lock Keeper system. By means of it, the possibility of direct attacks to a protected network can be eliminated entirely and data can be exchanged between two networks through a completely secure and reliable way. As an advanced implementation of this technology, the DualGate Lock-Keeper is proposed by including another new “gate” unit. Along with this development, not only the Lock -Keeper performance on data transfer, especially the transmit speed, is improved significantly, but also some other new good characteristics appear simultaneously. All these changes make the DualGate Lock-Keeper more efficient, flexible and applicable. Moreover, an architecture and its working principle of the Lock -Keeper Cluster which is built up by two DualGate Lock-Keeper are analyzed in detail in this paper.

The lock-keeper is a new network security solution which can provide secure data transfers between two different networks without having to establish a direct physical connection. By means of the lock-keeper system, the possibility of direct attacks to the protected network can be eliminated. An actual system, the singlegate lock-keeper, is used as an example to introduce the lock-keeper concept in detail, including its architecture, functionalities, applications, vulnerabilities and benefits. Based on this system, a new advanced dualgate lock-keeper including another "gate" unit is proposed that can provide more efficient and secure data exchange and make extensions of the lock-keeper applications possible.

One very popular software used to handle electronic conference submissions was written by the SIGACT Electronic Publishing Board. It was first used for the FOCS ’95 conference, and later for a range of conferences including COCOON, FOCS, PODC, SODA, SPAA, STOC, and WDAG, staying basically unchanged. Another conference in computer science that uses electronic submission mechanisms is the Symposium on Theoretical Aspects in Computer Science. STACS is an international conference covering all aspects of Theoretical Computer Science. It has proven to be - together with ICALP - the main European exchange place for ideas in this area. The program committee is internationally of top rank, the number of submissions is high (typically 100 to 140 papers), and the acceptance rate is low. Researchers come from all over the world to attend. Our experience is that the problems in the design of conference submission services can be grouped into the following categories:

As the focus of our work on electronic publishing, the department for Theoretical Computer Science at the University of Trier has developed methods and prototypical tools for use of the Internet in both kinds of publications since about mid-1994. While transfer of documents as-is can nowadays be considered everyday technology (which it wasn't, for several reasons, in 1994), and proper collection and processing of metadata is at least doable, the areas of mixed-platform document processing and support of the editorial process are still in the research phase. In this paper, we will focus on recent work in the latter area. In one of our projects — the Electronic Colloquium on Computational Complexity (ECCC), operative sind the end of 1994 — the decision process for selection of contributions to include was radically simplified in comparison to traditional journals. As a result, ECCC has a guaranteed limit on the delay between submission and decision of two months; many electronic journals use the same decision mechanism as paper journals, and suffer the same delays of sometimes over a year because of the time spent for communication between reviewers and editors. This approach could not be used, however, in the tools we developed for electronic conference submission. Conferences have established modi operandi, usually involving distribution of the submissions for reviewing down several hierarchical levels and an actual meeting of the editors (program committee, PC) for the final decision. As a consequence, the first tools we presented did not address the decision process at all, which left a large procedural hole between the actual electronic submission and the later support of final version submission and conference attendance. In 1999, we performed electronic submissions to the Symposium on Theoretical Aspects of Computer Science (STACS), and since the conference was hosted in Trier, we were able to “co-develop” certain changes in the decision process and a software implementing support for the entire process. The software performed well and demonstrated the anticipated advantages, the most memorable being publication of the list of accepted papers — formerly taking place up to a week after the PC meeting — while the assembled PC members watched.

The scientific community, especially the more computer related fields of science like computer science and mathematics, have not only been doing research in information technology, they have simultaneously begun to exploit its advantages for their own purposes. However, scientific publishing is different from other areas where information technology has been applied in that it requires publications to be not only fast, but also comparable to traditional media in terms of quality control and long-term availability. Peer reviewing and paper-based publishing are still the methods of choice to achieve the latter goals, restricting electronic means to more or less "inofficial" communications.Within the field of scientific communication, we find a number of types of communication with slightly different goal and character: From scientific journals with their extensive and, consequently, slow reviewing mechanisms over conference papers to - nowadays usually electronic - forms of publication by the author. On the other hand, and in spite of the delay incurred, peer review is advantageous: The remaining publications are reasonably filtered for quality, making the series worthwhile to read.The department for computer science at the University of Trier (Treves), Germany, is researching and implementing solutions in the area of information technology. In this paper, we will present one of our three main projects, the Electronic Colloquium on Computational Complexity (ECCC) We will introduce the specific situations it was developed for (Section 2.1), present the specific problems of interest and the chosen solutions (Section 2.3), and conclude with a report of current status and use (Section 2.4). Finally, we will outline our view of the future both for the field as a whole and for the specific project (Section 3).

The scientific community, especially the more computer related fields of science like computer science and mathematics, have not only been doing research in information technology, they have simultaneously begun to exploit its advantages for their own purposes. However, scientific publishing is different from other areas where information technology has been applied in that it requires publications to be not only fast, but also comparable to traditional media in terms of quality control and long-term availability. Peer reviewing and paper-based publishing are still the methods of choice to achieve the latter goals, restricting electronic means to more or less “inofficial” communications. Within the field of scientific communication, we find a number of types of communication with slightly different goal and character: From scientific journals with their extensive and, consequently, slow reviewing mechanisms over conference papers to nowadays usually electronic forms of publication by the anthor. On the other hand, and in spite of the delay incurred, peer review is advantageous: The remaining publications are reasonably filtered for quality, making the series, resp. conference proceedings, worthwhile to read. The department for computer science at the University of Trier (Treves), Germany, is researching and implementing solutions in the area of information technology. In this paper, we will present two of our three main projects. Meanwhile, our university has created the Center for Scientific Electronic Publishing (WEP) [6], which promotes the exchange of ideas on information technology and its applications between departments within the university. The projects presented in this paper are the Electronic Colloquium on Computational Complexity (ECCC) [7] and the STACS Electronic Submission Service 1151. For both, we will intro duce the specific situations they were developed Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage, and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prfor specific permission and/or a fee. 01999 ACM 1-59113-OM-x/s8DOO9 $9.00 for (Sections 2.1 and 3.1), present the specific problems of interest and the chosen solutions (Sections 2.3 and 3.2), and conclude with a report of current status and use (Sections 2.4 and 3.3). Finally, we will outline our view of the future both for the field as a whole and for the specific projects (Section 4).

Reduced ordered binary decision diagrams (OBDD's) are nowadays the state-of-the-art representation scheme for Boolean functions in Boolean manipulation. Recent results have shown that it is possible to use the more general concept of free binary decision diagrams (FBDD's) without giving up most of the useful computational properties of OBDD's, but possibly reducing the space requirements considerably. The amount of space reduction depends essentially on the shape of so-called FBDD-types the Boolean manipulation in terms of FBDD's is based on. Here, we propose some heuristics for deriving tree-like FBDD-types from given circuit descriptions. The experimental results we obtained clearly demonstrate that the FBDD-approach is not only of theoretical interest, but also of practical usefulness even in the ease of using merely such simple-structured tree-based FBDD-types as produced by the investigated heuristics.

We present the concept of TBDD's which considerably enlarges the class of Boolean functions that can be efficiently manipulated in terms of OBDD's. It extends the idea of using domain transformations, which is well-known in many areas of mathematics, physics, and technical sciences, to the context of OBDD-based Boolean function manipulation in CAD: Instead of working with the OBDD-representation of a function f, TBDD's allow working with an OBDD-representation of a suited cube transformed version of f. Besides of giving some theoretical insights into the new concept, we investigate in some detail cube transformations which are based on complete types. We - show that such TBDD-representations can be derived similarly as OBDD-representations, - give evidence of the practical importance of such TBDD's by presenting very small-size TBDD-representations of the hidden weighted bit functions HWBn which were proved to have only very large OBDD-representations, and - report some promising experimental results with some ISCAS benchmark circuits including the multiplier circuit C6288.

Electronic copies of technical reports are available: Via FTP: URL ftp://ftp.informatik.uni-trier.de/pub/Users-Root/reports Via WWW: URL http://www.informatik.uni-trier.de/Reports/Current.html Via email: Send a mail to ftpmail@ftp.informatik.uni-trier.de, subject ’HELP’, for detailed instructions Printed copies: Trierer Forschungsberichte Fachbereich IV Mathematik / Informatik Universitat Trier ..

It is shown that Free Binary Decision Diagrams (FBDD's), with respect to a predefined type, provide a canonical representation and allow efficient solutions of the basic tasks in Boolean manipulation in a similar manner to the well-known OBDD's. However, in contrast to OBDD's, the FBDD's allow more succinct representations of Boolean functions. For experimentation we have used an FBDD-package and the types worked with are tree-based. Using different type-creating heuristics, we compare the size of FBDD-representations of some ISCAS benchmarks with the size of their OBDD-representations

It is shown that Free Binary Decision Diagrams (FBDD's), with respect to a predeened type, provide a canonical representation and allow eecient solutions of the basic tasks in Boolean manipulation similarly as the well{known OBDD's do. But in contrast to OBDD's, typed FBDD's allow more succinct representations of Boolean functions. For experimentation we have used an FBDD{ package. The types we work with are tree{based. Due to diierent type{creating heuristics we compare the size of FBDD{representations of some ISCAS benchmarks with the size of their OBDD{representations.