Streaming Tree Transducers

Theory of tree transducers provides a foundation for understanding expressiveness and complexity of analysis problems for specification languages for transforming hierarchically structured data such as XML documents. We introduce streaming tree transducers as an analyzable, executable, and expressive model for transforming unranked ordered trees in a single pass. Given a linear encoding of the input tree, the transducer makes a single left-to-right pass through the input, and computes the output in linear time using a finite-state control, a visibly pushdown stack, and a finite number of variables that store output chunks that can be combined using the operations of string-concatenation and tree-insertion. We prove that the expressiveness of the model coincides with transductions definable using monadic second-order logic (MSO). Existing models of tree transducers either cannot implement all MSO-definable transformations, or require regular look ahead that prohibits single-pass implementation. We show a variety of analysis problems such as type-checking and checking functional equivalence are solvable for our model.Comment: 40 page

On Functionality of Visibly Pushdown Transducers

Visibly pushdown transducers form a subclass of pushdown transducers that (strictly) extends finite state transducers with a stack. Like visibly pushdown automata, the input symbols determine the stack operations. In this paper, we prove that functionality is decidable in PSpace for visibly pushdown transducers. The proof is done via a pumping argument: if a word with two outputs has a sufficiently large nesting depth, there exists a nested word with two outputs whose nesting depth is strictly smaller. The proof uses technics of word combinatorics. As a consequence of decidability of functionality, we also show that equivalence of functional visibly pushdown transducers is Exptime-Complete.Comment: 20 page

Causality and replication in concurrent processes

The replication operator was introduced by Milner for obtaining a simplified description of recursive processes. The standard interleaving semantics denotes the replication of a process P, written !P, a shorthand for its unbound parallel composition, operationally equivalent to the process P | P | …, with P repeated as many times as needed. Albeit the replication mechanism has become increasingly popular, investigations on its causal semantics has been scarce. In fact, the correspondence between replication and unbound parallelism makes it difficult to recover basic properties usually associated with these semantics, such as the so-called concurrency diamond. In this paper we consider the interleaving semantics for the operator proposed by Sangiorgi and Walker, and we show how to refine it in order to capture causality. Furthermore, we prove it coincident with the standard causal semantics for recursive process studied in the literature, for processes defined by means of constant invocations

Reachability in Higher-Order-Counters

Higher-order counter automata (\HOCS) can be either seen as a restriction of higher-order pushdown automata (\HOPS) to a unary stack alphabet, or as an extension of counter automata to higher levels. We distinguish two principal kinds of \HOCS: those that can test whether the topmost counter value is zero and those which cannot. We show that control-state reachability for level $k$ \HOCS with $0$-test is complete for \mbox{$(k-2)$}-fold exponential space; leaving out the $0$-test leads to completeness for \mbox{$(k-2)$}-fold exponential time. Restricting \HOCS (without $0$-test) to level $2$, we prove that global (forward or backward) reachability analysis is \PTIME-complete. This enhances the known result for pushdown systems which are subsumed by level $2$ \HOCS without $0$-test. We transfer our results to the formal language setting. Assuming that \PTIME \subsetneq \PSPACE \subsetneq \mathbf{EXPTIME}, we apply proof ideas of Engelfriet and conclude that the hierarchies of languages of \HOPS and of \HOCS form strictly interleaving hierarchies. Interestingly, Engelfriet's constructions also allow to conclude immediately that the hierarchy of collapsible pushdown languages is strict level-by-level due to the existing complexity results for reachability on collapsible pushdown graphs. This answers an open question independently asked by Parys and by Kobayashi.Comment: Version with Full Proofs of a paper that appears at MFCS 201

Testosterone: Bad for Men, Good for Women?

# The Author(s) 2010. This article is published with open access at Springerlink.com Generally, high testosterone levels within the physiological range are associated with a more favourable cardiometabolic profile. Although the FDA has approved testosterone for use only in men with hypogonadism, whose sex glands produce extremely low amounts of testosterone, off-label use has dramatically increased in recent years. In the past two decades, there has been a huge increase in testosterone prescriptions, and many trials have shown benefit in terms of risk factor modification and symptoms. These observations fit also into the picture that reduced testosterone levels in men are associated with increased cardiovascular risk inducing elevated triglyceride levels, low high-density lipoprotein (HDL) cholesterol levels, central obesity, glucose intolerance, and diabetes. This has recently been demonstrated by Malkin et al. (October 26 issue, 2010, Heart), who showed that low testosterone levels (total testosterone <8.1 nmol/l) are associated with early death in men with heart disease. The longitudinal follow-up study involved 930 men with coronary heart disease for a period of about 7 years. During the study period, 41 of 194 (21%) men with low testosterone levels died compared with 88 of 736 (12%) men with normal levels of the hormone (p=0.002). It was concluded that, if androgen deficiency is part of the underlying pathophysiology of atherosclerotic disease in men, the serum testosterone level could be viewed as a favourable modifiable risk factor. However, this view has been challenged by Basaria et al

On the tree-transformation power of XSLT

XSLT is a standard rule-based programming language for expressing transformations of XML data. The language is currently in transition from version 1.0 to 2.0. In order to understand the computational consequences of this transition, we restrict XSLT to its pure tree-transformation capabilities. Under this focus, we observe that XSLT~1.0 was not yet a computationally complete tree-transformation language: every 1.0 program can be implemented in exponential time. A crucial new feature of version~2.0, however, which allows nodesets over temporary trees, yields completeness. We provide a formal operational semantics for XSLT programs, and establish confluence for this semantics

Delivery of care for adult patients with congenital heart disease in Europe: Results from the Euro Heart Survey

Aims: The increasing number of adults with congenital heart disease (CHD) has prompted the development of recommendations for the management of these patients and for the organization of their healthcare. The aim of this report is to describe the delivery of care in Europe for adults with congenital cardiac anomalies. Methods and results: As part of the Euro Heart Survey on Adult Congenital Heart Disease, we obtained data from 71 voluntarily participating centres that detailed their care practices for these patients. Forty-eight of these centres were specialist centres and 23 were non-specialist centres. We found that only 19% of the specialist centres complied with defined standards for optimal care structure. The criteria that appeared to be most difficult for all centres to achieve were performing 50 congenital heart operations or more per year and involving nurse specialists in the care of these patients. Conclusion: This survey indicated that the provision of care in Europe for adults with congenital