12 research outputs found
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Containment and equivalence of weighted automata: Probabilistic and max-plus cases
This paper surveys some results regarding decision problems for probabilistic and max-plus automata, such as containment and equivalence. Probabilistic and max-plus automata are part of the general family of weighted automata, whose semantics are maps from words to real values. Given two weighted automata, the equivalence problem asks whether their semantics are the same, and the containment problem whether one is point-wise smaller than the other one. These problems have been studied intensively and this paper will review some techniques used to show (un)decidability and state a list of open questions that still remain
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Register complexity and determinisation of max-plus automata
We survey some results about the sequentiality problem for max-plus automata and its generalisation, the register complexity problem for cost register automata. We compare classes of functions computed by maxplus automata and by cost register automata with respect to the notion of ambiguity. The two models are introduced gently, so the novice reader is welcome
Recognizable tree series with discounting
We consider weighted tree automata with discounting over commutative semirings. For their behaviors we establish a Kleene theorem and an MSO-logic characterization. We introduce also weighted Muller tree automata with discounting over the max-plus and the min-plus semirings, and we show their expressive equivalence with two fragments of weighted MSO-sentences
Computations by fly-automata beyond monadic second-order logic
We present logically based methods for constructing XP and FPT graph
algorithms, parametrized by tree-width or clique-width. We will use
fly-automata introduced in a previous article. They make possible to check
properties that are not monadic second-order expressible because their states
may include counters, so that their sets of states may be infinite. We equip
these automata with output functions, so that they can compute values
associated with terms or graphs. Rather than new algorithmic results we present
tools for constructing easily certain dynamic programming algorithms by
combining predefined automata for basic functions and properties.Comment: Accepted for publication in Theoretical Computer Scienc
Inclusion Diagrams for Classes of Deterministic Bottom-up Tree-to-Tree-Series Transformations
In this paper we investigate the relationship between classes of tree-to-tree-series (for short: t-ts) and o-tree-to-tree-series (for short: o-t-ts) transformations computed by restricted deterministic bottom-up weighted tree transducers (for short: deterministic bu-w-tt). Essentially, deterministic bu-w-tt are deterministic bottom-up tree series transducers [EFV02, FV03, ful, FGV04], but the former are de ned over monoids whereas the latter are de ned over semirings and only use the multiplicative monoid thereof. In particular, the common restrictions of non-deletion, linearity, totality, and homomorphism [Eng75] can equivalently be de ned for deterministic bu-w-tt.
Using well-known results of classical tree transducer theory (cf., e.g., [Eng75, FĂĽl91]) and also new results on deterministic bu-w-tt, we order classes of t-ts and o-t-ts transformations computed by restricted deterministic bu-w-tt by set inclusion. More precisely, for every commutative monoid we completely specify the inclusion relation of the classes of t-ts and o-t-ts transformations for all sensible combinations of restrictions by means of inclusion diagrams
A pumping lemma and decidability problems for recognizable tree series
In the present paper we show that given a tree series S, which is accepted by (a) a deterministic bottom-up finite state weighted tree automaton (for short: bu-w-fta) or (b) a non-deterministic bu-w-fta over a locally finite semiring, there exists for every input tree t E supp(S) a decomposition t = C'[C[s]] into contexts C, C' and an input tree s as well as there exist semiring elements a, a', b, b', c such that the equation (S,C'[Cn[s]]) = a'OanOcObnOb' holds for every non-negative integer n. In order to prove this pumping lemma we extend the power-set construction of classical theories and show that for every non-deterministic bu-w-fta over a locally finite semiring there exists an equivalent deterministic one. By applying the pumping lemma we prove the decidability of a tree series S being constant on its support, S being constant, S being boolean, the support of S being the empty set, and the support of S being a finite set provided that S is accepted by (a) a deterministic bu-w-fta over a commutative semiring or (b) a non-deterministic bu-w-fta over a locally finite commutative semiring
Crisp-determinization of weighted tree automata over strong bimonoids
We consider weighted tree automata (wta) over strong bimonoids and their
initial algebra semantics and their run semantics. There are wta for which
these semantics are different; however, for bottom-up deterministic wta and for
wta over semirings, the difference vanishes. A wta is crisp-deterministic if it
is bottom-up deterministic and each transition is weighted by one of the unit
elements of the strong bimonoid. We prove that the class of weighted tree
languages recognized by crisp-deterministic wta is the same as the class of
recognizable step mappings. Moreover, we investigate the following two
crisp-determinization problems: for a given wta , (a) does there
exist a crisp-deterministic wta which computes the initial algebra semantics of
and (b) does there exist a crisp-deterministic wta which computes
the run semantics of ? We show that the finiteness of the Nerode
algebra of implies a positive answer for (a),
and that the finite order property of implies a positive answer for
(b). We show a sufficient condition which guarantees the finiteness of and a sufficient condition which guarantees the finite order
property of . Also, we provide an algorithm for the construction of
the crisp-deterministic wta according to (a) if is finite,
and similarly for (b) if has finite order property. We prove that it
is undecidable whether an arbitrary wta is crisp-determinizable. We
also prove that both, the finiteness of and the finite
order property of are undecidable
Gewichtete Logik und Baumautomaten ĂĽber Baumbewertungsmonoiden
Bäume sind wichtige Strukturen in der Informatik. Sie repräsentieren zum Beispiel Programmcode oder Datenstrukturen. Ihre quantitativen Eigenschaften, wie zum Beispiel ihr Ressourcenverbrauch, können mittels gewichteten Baumautomaten un- tersucht werden. Wir definieren neue gewichtete endliche Bottom-Up-Baumautoma- ten mit Gewichten aus Baumbewertungsmonoiden. Baumbewertungsmonoide sind verallgemeinerte Bewertungsmonoide mit einer Bewertungsfunktion, die auf Bäumen operiert. Sie ermöglichen es, unter anderem, den durchschnittlichen Ressourcenver- brauch zu modellieren. Des Weiteren führen wir eine gewichtete Logik für Bäume mit Gewichten aus Baumbewertungsmonoiden ein und zeigen, in Abhängigkeit von den Eigenschaften des Bewertungsmonoids, dass Fragmente dieser Logik die Klasse der erkennbaren Baumreihen über dem Baumbewertungsmonoid charakterisieren. Damit verallgemeinern wir das Resultat von Droste und Meinecke [17] von Wort- reihen über Bewertungsmonoiden auf Baumreihen über Baumbewertungsmonoiden. Schließlich geben wir Beispiele an, die die Notwendigkeit der Einschränkung der betrachteten Baumbewertungmonoide belegen
Multioperator Weighted Monadic Datalog
In this thesis we will introduce multioperator weighted monadic datalog (mwmd), a formal model for specifying tree series, tree transformations, and tree languages. This model combines aspects of multioperator weighted tree automata (wmta), weighted monadic datalog (wmd), and monadic datalog tree transducers (mdtt). In order to develop a rich theory we will define multiple versions of semantics for mwmd and compare their expressiveness. We will study normal forms and decidability results of mwmd and show (by employing particular semantic domains) that the theory of mwmd subsumes the theory of both wmd and mdtt. We conclude this thesis by showing that mwmd even contain wmta as a syntactic subclass and present results concerning this subclass