205885836
On Predecessors of Finite Languages
We continue the study of finite grammatical families by characterizing when a family has a predecessor. This characterization implies that (i) the existence of predecessors for finite families is decidable and (ii) the collection of context-free grammatical families, each family of which contains all regular languages, is not maximal dense.
39074040
Pure Grammars
7533318
Completeness of Context-Free Grammar Forms
The notions of a grammar form and g-interpretation were first introduced in [2]. However, it quickly became apparent, particularly for EOL forms [5], that (strict) interpretations had a wider interest as well as being better motivated mathematically. The study of parsing of grammar forms detailed in [4], the basic investigation in [8] on linear completeness amongst other results, the study of density in [9, lo] and the connections with graph theory shown in [ 1 l] have affirmed this position. The present paper continues the approach of [8] focussing on the characterization of complete grammar forms, that is grammar forms which generate all’ context-free languages. Some decidability problems will also be discussed. For further morivation and background material we refer the reader to [8, 141, while for all unexplained concepts in language theory, see [ 131. After giving the necessary definitions in the remainder of this section we characterize complete grammar forms in Section 2, 3 and 4. In Section 2 we introduce the central concept of expansion spectrum and in Section 3 the recently proved super normal form theorem [ 121, while in Section 4 the characterization is completed and generators and hierarchies are briefly mentioned. Consider context-free grammars G = (V, C, P, S), where Z is the alphabet of terminals, VZ the alphabet of nonterminals, P is the set of productions and
39838781
Context-Free Grammar Forms with Strict Interpretations
This paper begins a systematic investigation of context-free grammar forms using the mechanism of “strict” interpretations: the interpretations of terminal letters are defined exactly as those of nonterminal letters. Thus, strict interpretations are more closely related to the master grammar than the g-interpretations investigated in the original grammar form paper [A. Cremers and S. Ginsburg, Context-free grammar forms, J. Comput. System Sci. 11 (1975), 86–116]. The main results of this paper concern reducibility, closure properties, generators and hierarchies of language families, as well as the characterization of grammar forms generating (under strict interpretation) the families of regular and linear languages.
21847551
Bounded Delay L Codes
Abstract Three natural notions of bounded delay for L codes are investigated. All interrelations, many of them rather surprising, between ordinary codes of bounded delay and L codes of bounded delay of various types are established.
30874363
Synchronized EOL Forms Under Uniform Interpretation
— The aim ofthis paper is thejurther study oj EOLjorms under uniform interprétation. We are naturally led to the considération oj synchronized EOLjorms, which become the central thème of this paper. We prove: a ""strongest"" possible normaljorm resuit, the spanning normalJorm theorem; the non-existence oj uni-generatorsjor "reasonable" language amilies, which include thefinite, regular and context-jree j amilies; and a char act erization oj those ynchronized jorms which, under uniform interprétation, yield all regular languages. In closing we remark on three topics which are worthy oj separate investigation. Résumé. — Le but de cet article est de poursuivre l'étude des EOL-jormes sous des interprétations unijormes. Nous sommes conduits naturellement à considérer les EOL-jormes synchronisées qui deviennent le thème central de cet article. Nous établissons : un résultat sur la forme normale la plus « serrée » possible, le théorème sur la forme normale recouvrante, la non-existence d'uni-générateurs pour des jamilles « raisonnables » de langages qui comprennent les langages finis, rationnels et algébriques; et une caractérisation des formes synchronisées qui donnent, par interprétation unijorme, tous les langages rationnels. Pour terminer, nous effleurons trois domaines qui méritent une étude séparée.
13899040
The Regularity of Two-Way Nondeterministic Tree Automata Languages
We establish that regularly extended two-way nondeterministic tree automata with unranked alphabets have the same expressive power as regularly extended nondeterministic tree automata with unranked alphabets alphabets. We obtain this results by establishing regularly extended versions of a congruence on trees and of a congruence on, so called, views. Our motivation for the study of these tree models is the Extensible Markup Language (XML), a metalanguage for defining document grammars. Such grammars have regular sets of right-hand sides for their productions and tree automata provide an alternative and useful modeling tool for them. In particular, we believe that they provide a useful computational model for what we call caterpillar expressions.
17637821
IPC Considered Harmful for Multiprocessor Workloads
Many architectural simulation studies use instructions per cycle (IPC) to analyze performance. In this article, we challenge the commonly held view that IPC accurately reflects performance - at least for multithreaded workloads running on multiprocessors. Work-related metrics, such as time per transaction, are the most accurate and reliable way to estimate multiprocessor workload performance
2381269
Track Layouts of Graphs
Graph drawing problems originate from diverse application domains. In some, such as software engineering and cartography, graphs are required to be visualized or drawn in ways that are easy to read and understand. In others, such as VLSI design, graphs are required to be laid out while satisfying some physical constraint. For example, when a drawing is to be displayed on a page or a computer screen, or is to be used for VLSI design, it is important to keep its area/volume small to avoid wasting space. 
More often than not however, the idea of a good drawing, regardless of its purpose, coincides with having no edge crossings or having very few crossings. Unfortunately, whichever of the numerous drawing styles one considers, a problem requiring a crossing minimization of sorts will, almost certainly, be NP -hard. The theory of fixed parameter tractability (FPT) provides a new and promising approach for coping with intractable problems. In the first part of this thesis we apply algorithmic techniques developed in this theory to well-known graph drawing problems. In particular, we contribute efficient FPT algorithms for crossing minimization and planarization problems concerning the 2-layer drawing style. 
In the second part of this thesis we introduce and comprehensively study so-called track layouts of graphs and their subdivisions. A relationship between this combinatorial structure and several well-known types of graph layouts is established, leading to a number of new results. For example, our study of track layouts of bounded treewidth graphs settles an open problem due to Ganley and Heath (2001) regarding queue layouts of such graphs. Moreover, the study also establishes that graphs of bounded treewidth have three-dimensional straight-line grid drawings with linear volume. 
Through the study of track layouts of subdivisions, we determine that every graph with n vertices and m edges has a three-dimensional polyline grid drawing with the vertices on a rectangular prism, O (n + m log n) volume and O (log n) bends per edge.
125792
Upward Three-Dimensional Grid Drawings of Graphs
A three-dimensional grid drawing of a graph is a placement of the vertices at distinct points with integer coordinates, such that the straight line segments representing the edges do not cross. Our aim is to produce three-dimensional grid drawings with small bounding box volume. Our first main result is that every $n$-vertex graph with bounded degeneracy has a three-dimensional grid drawing with $\mathcal{O}\left({n^{3/2}}\right)$ volume. This is the largest known class of graphs that have such drawings. A three-dimensional grid drawing of a directed acyclic graph (dag) is upward if every arc points up in the $\textsf{z}$-direction. We prove that every dag has an upward three-dimensional grid drawing with $\mathcal{O}\left({n^3}\right)$ volume, which is tight for the complete dag. The previous best upper bound was $\mathcal{O}\left({n^4}\right)$. Our main result concerning upward drawings is that every $c$-colourable dag ($c$ constant) has an upward three-dimensional grid drawing with $\mathcal{O}\left({n^2}\right)$ volume. This result matches the bound in the undirected case, and improves the best known bound from $\mathcal{O}\left({n^3}\right)$ for many classes of dags, including planar, series parallel, and outerplanar. Improved bounds are also obtained for tree dags. We prove a strong relationship between upward three-dimensional grid drawings, upward track layouts, and upward queue layouts. Finally, we study upward three-dimensional grid drawings with bends in the edges.
14349700
Normal form algorithms for extended context-free grammars
We investigate the complexity of a variety of normal-form transformations for extended context-free grammars, where by extended we mean that the set of right-hand sides for each nonterminal in such a grammar is a regular set. The study is motivated by the implementation project GraMa which will provide a C++ toolkit for the symbolic manipulation of context-free objects just as Grail does for regular objects. Our results generalize known complexity bounds for context-free grammars but do so in nontrivial ways. Specifically, we introduce a new representation scheme for extended context-free grammars (the symbol-threaded expression forest), a new normal form for these grammars (dot normal form) and new regular expression algorithms. Copyright 2001 Elsevier Science B.V.