Context-awareness refers to systems that unobtrusively adapt to the environment of their users on the basis of context information, popularly known as contextaware systems. One inherent property of context information is that it possesses a certain quality, such as the certainty with which it has been determined and so on. Different aspects of this quality are represented by a set of indicators...

The assignment of probabilities to the productions of a context-free grammar may generate an improper distribution: the probability of all finite parse trees is less than one. The condition for proper assignment is rather subtle. Production probabilities can be estimated from parsed or unparsed sentences, and the question arises as to whether or not an estimated system is automatically proper. ...

We study the following problem: given two words w and x, with jwj; jxj n, what is the size of the smallest context-free grammar G which generates exactly one of fw; xg? If jwj 6 = jxj, then we prove there exists a G separating w from x of size O(log log n), and this bound is best possible. If jwj = jxj, then we get an upper bound on the size of G of O(log n), and a lower bound of (logn loglog n).

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This paper answers three open questions concerning the generative power of some simple variants of context-free grammars regulated by context conditions. Specifically, it discusses the generative power of so-called contextfree semi-conditional grammars (which are random context grammars where permitting and forbidding sets are replaced with permitting and forbidding strings) where permitting an...

We show that, given a string s of length n, with constant memory and logarithmic passes over a constant number of streams we can build a context-free grammar that generates s and only s and whose size is within an O (

The ability to detect ambiguities in context-free grammars is vital for their use in several fields, but the problem is undecidable in the general case. We present a safe, conservative approach, where approximations cannot result in overlooked ambiguous cases. We analyze the complexity of its use, and compare it with other ambiguity detection methods.

We investigate several kinds of regulated rewriting (programmed, matrix, with regular control, ordered, and variants thereof) and of parallel rewriting mechanisms (Lindenmayer systems, uniformly limited Lindenmayer systems, limited Lindenmayer systems and scattered context grammars) as accepting devices, in contrast with the usual generating mode. In some cases, accepting mode turns out to be j...

We introduce a large family of k-context-free sequences for wich we give a polynomial upper bound of their complexity functions.

In this paper, we study some periodicity concepts on words. First, we extend the notion of full tilings which was recently introduced by Karhumäki, Lifshits, and Rytter to partial tilings. Second, we investigate the notion of quasiperiods and show in particular that the set of quasiperiodic words is a context-sensitive language that is not context-free, answering a conjecture by Dömösi, Horváth...