394 research outputs found
Node Query Preservation for Deterministic Linear Top-Down Tree Transducers
This paper discusses the decidability of node query preservation problems for
XML document transformations. We assume a transformation given by a
deterministic linear top-down data tree transducer (abbreviated as DLT^V) and
an n-ary query based on runs of a tree automaton. We say that a DLT^V Tr
strongly preserves a query Q if there is a query Q' such that for every
document t, the answer set of Q' for Tr(t) is equal to the answer set of Q for
t. Also we say that Tr weakly preserves Q if there is a query Q' such that for
every t_d in the range of Tr, the answer set of Q' for t_d is equal to the
union of the answer set of Q for t such that t_d = Tr(t). We show that the weak
preservation problem is coNP-complete and the strong preservation problem is in
2-EXPTIME.Comment: In Proceedings TTATT 2013, arXiv:1311.505
Linear Bounded Composition of Tree-Walking Tree Transducers: Linear Size Increase and Complexity
Compositions of tree-walking tree transducers form a hierarchy with respect
to the number of transducers in the composition. As main technical result it is
proved that any such composition can be realized as a linear bounded
composition, which means that the sizes of the intermediate results can be
chosen to be at most linear in the size of the output tree. This has
consequences for the expressiveness and complexity of the translations in the
hierarchy. First, if the computed translation is a function of linear size
increase, i.e., the size of the output tree is at most linear in the size of
the input tree, then it can be realized by just one, deterministic,
tree-walking tree transducer. For compositions of deterministic transducers it
is decidable whether or not the translation is of linear size increase. Second,
every composition of deterministic transducers can be computed in deterministic
linear time on a RAM and in deterministic linear space on a Turing machine,
measured in the sum of the sizes of the input and output tree. Similarly, every
composition of nondeterministic transducers can be computed in simultaneous
polynomial time and linear space on a nondeterministic Turing machine. Their
output tree languages are deterministic context-sensitive, i.e., can be
recognized in deterministic linear space on a Turing machine. The membership
problem for compositions of nondeterministic translations is nondeterministic
polynomial time and deterministic linear space. The membership problem for the
composition of a nondeterministic and a deterministic tree-walking tree
translation (for a nondeterministic IO macro tree translation) is log-space
reducible to a context-free language, whereas the membership problem for the
composition of a deterministic and a nondeterministic tree-walking tree
translation (for a nondeterministic OI macro tree translation) is possibly
NP-complete
08171 Abstracts Collection -- Beyond the Finite: New Challenges in Verification and Semistructured Data
From 20.04. to 25.04.2008, the Dagstuhl Seminar 08171 ``Beyond the Finite: New Challenges in Verification and Semistructured Data\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Evaluation of XPath Queries against XML Streams
XML is nowadays the de facto standard for electronic data
interchange on the Web. Available XML data ranges from small Web pages to ever-growing repositories of, e.g., biological and astronomical data, and even to rapidly changing and possibly unbounded streams, as used in Web data integration and publish-subscribe systems.
Animated by the ubiquity of XML data, the basic task of XML querying is becoming of great theoretical and practical importance. The last years witnessed efforts as well from practitioners, as also from theoreticians towards defining an appropriate XML query language. At the core of this common effort has been identified a navigational approach for information localization in XML data, comprised in a
practical and simple query language called XPath.
This work brings together the two aforementioned ``worlds'', i.e., the XPath query evaluation and the XML data streams, and shows as well theoretical as also practical relevance of this fusion. Its relevance can not be subsumed by traditional database management systems, because the latter are not designed for rapid and continuous loading of individual data items, and do not directly support the continuous queries that are typical for stream applications.
The first central contribution of this work consists in the definition and the theoretical investigation of three term rewriting systems to rewrite queries with reverse predicates, like parent or ancestor, into equivalent forward queries, i.e., queries without reverse predicates. Our rewriting approach is vital to the evaluation of queries with reverse predicates against unbounded XML streams, because neither the storage of past fragments of the stream, nor several stream traversals, as required by the evaluation of reverse predicates, are affordable.
Beyond their declared main purpose of providing equivalences between queries with reverse predicates and forward queries, the applications of our rewriting systems shed light on other query language properties, like the expressivity of some of its fragments, the query minimization, or even the
complexity of query evaluation. For example, using these systems, one can rewrite any graph query into an equivalent forward forest query.
The second main contribution consists in a streamed and progressive evaluation strategy of forward queries against XML streams. The evaluation is specified using compositions of so-called stream processing functions, and is implemented using networks of deterministic pushdown transducers. The
complexity of this evaluation strategy is polynomial in both the query and the data sizes for forward forest queries and even for a large fragment of graph queries.
The third central contribution consists in two real monitoring applications that use directly the results of this work: the monitoring of processes running on UNIX computers, and a system for providing graphically real-time traffic and travel information, as broadcasted within ubiquitous radio signals
Stream Processing using Grammars and Regular Expressions
In this dissertation we study regular expression based parsing and the use of
grammatical specifications for the synthesis of fast, streaming
string-processing programs.
In the first part we develop two linear-time algorithms for regular
expression based parsing with Perl-style greedy disambiguation. The first
algorithm operates in two passes in a semi-streaming fashion, using a constant
amount of working memory and an auxiliary tape storage which is written in the
first pass and consumed by the second. The second algorithm is a single-pass
and optimally streaming algorithm which outputs as much of the parse tree as is
semantically possible based on the input prefix read so far, and resorts to
buffering as many symbols as is required to resolve the next choice. Optimality
is obtained by performing a PSPACE-complete pre-analysis on the regular
expression.
In the second part we present Kleenex, a language for expressing
high-performance streaming string processing programs as regular grammars with
embedded semantic actions, and its compilation to streaming string transducers
with worst-case linear-time performance. Its underlying theory is based on
transducer decomposition into oracle and action machines, and a finite-state
specialization of the streaming parsing algorithm presented in the first part.
In the second part we also develop a new linear-time streaming parsing
algorithm for parsing expression grammars (PEG) which generalizes the regular
grammars of Kleenex. The algorithm is based on a bottom-up tabulation algorithm
reformulated using least fixed points and evaluated using an instance of the
chaotic iteration scheme by Cousot and Cousot
Rewrite based Verification of XML Updates
We consider problems of access control for update of XML documents. In the
context of XML programming, types can be viewed as hedge automata, and static
type checking amounts to verify that a program always converts valid source
documents into also valid output documents. Given a set of update operations we
are particularly interested by checking safety properties such as preservation
of document types along any sequence of updates. We are also interested by the
related policy consistency problem, that is detecting whether a sequence of
authorized operations can simulate a forbidden one. We reduce these questions
to type checking problems, solved by computing variants of hedge automata
characterizing the set of ancestors and descendants of the initial document
type for the closure of parameterized rewrite rules
Foundations of Software Science and Computation Structures
This open access book constitutes the proceedings of the 24th International Conference on Foundations of Software Science and Computational Structures, FOSSACS 2021, which was held during March 27 until April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The 28 regular papers presented in this volume were carefully reviewed and selected from 88 submissions. They deal with research on theories and methods to support the analysis, integration, synthesis, transformation, and verification of programs and software systems
Efficient Inclusion Checking for Deterministic Tree Automata and XML Schemas
Special issue of LATA'08.International audienceWe present algorithms for testing language inclusion L(A) ⊆ L(B) between tree automata in time O(|A| |B|) where B is deterministic (bottom-up or top-down). We extend our algorithms for testing inclusion of automata for unranked trees A in deterministic DTDs or deterministic EDTDs with restrained competition D in time O(|A| |Σ| |D|). Previous algorithms were less efficient or less general
- …