2,863 research outputs found
The copying power of one-state tree transducers
One-state deterministic top-down tree transducers (or, tree homomorphisms) cannot handle "prime copying," i.e., their class of output (string) languages is not closed under the operation L → {)f(n) w ε L, f(n) ≥ 1}, where f is any integer function whose range contains numbers with arbitrarily large prime factors (such as a polynomial). The exact amount of nonclosure under these copying operations is established for several classes of input (tree) languages. These results are relevant to the extended definable (or, restricted parallel level) languages, to the syntax-directed translation of context-free languages, and to the tree transducer hierarchy.\ud
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Synthesis of Deterministic Top-down Tree Transducers from Automatic Tree Relations
We consider the synthesis of deterministic tree transducers from automaton
definable specifications, given as binary relations, over finite trees. We
consider the case of specifications that are deterministic top-down tree
automatic, meaning the specification is recognizable by a deterministic
top-down tree automaton that reads the two given trees synchronously in
parallel. In this setting we study tree transducers that are allowed to have
either bounded delay or arbitrary delay. Delay is caused whenever the
transducer reads a symbol from the input tree but does not produce output. We
provide decision procedures for both bounded and arbitrary delay that yield
deterministic top-down tree transducers which realize the specification for
valid input trees. Similar to the case of relations over words, we use
two-player games to obtain our results.Comment: In Proceedings GandALF 2014, arXiv:1408.556
Toward Security Verification against Inference Attacks on Data Trees
This paper describes our ongoing work on security verification against
inference attacks on data trees. We focus on infinite secrecy against inference
attacks, which means that attackers cannot narrow down the candidates for the
value of the sensitive information to finite by available information to the
attackers. Our purpose is to propose a model under which infinite secrecy is
decidable. To be specific, we first propose tree transducers which are
expressive enough to represent practical queries. Then, in order to represent
attackers' knowledge, we propose data tree types such that type inference and
inverse type inference on those tree transducers are possible with respect to
data tree types, and infiniteness of data tree types is decidable.Comment: In Proceedings TTATT 2013, arXiv:1311.505
Three hierarchies of transducers
Composition of top-down tree transducers yields a proper hierarchy of transductions and of output languages. The same is true for ETOL systems (viewed as transducers) and for two-way generalized sequential machines
Two-Way Visibly Pushdown Automata and Transducers
Automata-logic connections are pillars of the theory of regular languages.
Such connections are harder to obtain for transducers, but important results
have been obtained recently for word-to-word transformations, showing that the
three following models are equivalent: deterministic two-way transducers,
monadic second-order (MSO) transducers, and deterministic one-way automata
equipped with a finite number of registers. Nested words are words with a
nesting structure, allowing to model unranked trees as their depth-first-search
linearisations. In this paper, we consider transformations from nested words to
words, allowing in particular to produce unranked trees if output words have a
nesting structure. The model of visibly pushdown transducers allows to describe
such transformations, and we propose a simple deterministic extension of this
model with two-way moves that has the following properties: i) it is a simple
computational model, that naturally has a good evaluation complexity; ii) it is
expressive: it subsumes nested word-to-word MSO transducers, and the exact
expressiveness of MSO transducers is recovered using a simple syntactic
restriction; iii) it has good algorithmic/closure properties: the model is
closed under composition with a unambiguous one-way letter-to-letter transducer
which gives closure under regular look-around, and has a decidable equivalence
problem
Tree transducers, L systems, and two-way machines
A relationship between parallel rewriting systems and two-way machines is investigated. Restrictions on the “copying power” of these devices endow them with rich structuring and give insight into the issues of determinism, parallelism, and copying. Among the parallel rewriting systems considered are the top-down tree transducer; the generalized syntax-directed translation scheme and the ETOL system, and among the two-way machines are the tree-walking automaton, the two-way finite-state transducer, and (generalizations of) the one-way checking stack automaton. The. relationship of these devices to macro grammars is also considered. An effort is made .to provide a systematic survey of a number of existing results
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