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There is a trade-off between performance and correctness in implementing concurrent data structures. Better performance may be achieved at the expense of relaxing correctness, by redefining the semantics of data structures. We address such a redefinition of data structure semantics and present a systematic and formal framework for obtaining new data structures by quantitatively relaxing existing ones. We view a data structure as a sequential specification containing all "legal" sequences over an alphabet of method calls. Relaxing the data structure corresponds to defining a distance from any sequence over the alphabet to the sequential specification: the k-relaxed sequential specification contains all sequences over the alphabet within distance k from the original specification. In contrast to other existing work, our relaxations are semantic (distance in terms of data structure states). As an instantiation of our framework, we present two simple yet generic relaxation schemes, called out-of-order and stuttering relaxation, along with several ways of computing distances. We show that the out-of-order relaxation, when further instantiated to stacks, queues, and priority queues, amounts to tolerating bounded out-of-order behavior, which cannot be captured by a purely syntactic relaxation (distance in terms of sequence manipulation, e.g. edit distance). We give concurrent implementations of relaxed data structures and demonstrate that bounded relaxations provide the means for trading correctness for performance in a controlled way. The relaxations are monotonic, which further highlights the trade-off: increasing k increases the number of permitted sequences, which as we demonstrate can lead to better performance. Finally, since a relaxed stack or queue also implements a pool, we obtain new concurrent pool implementations that outperform the state-of-the-art ones.

Within the complex signalling network from pathogen-derived elicitor perception to defense-related gene activation, some immediate-early responding genes may have pivotal roles in downstream transcriptional regulation. We have identified the parsley (Petroselinum crispum) ELI17 gene as a particularly fast-responding gene possessing a new type of W box-containing, elicitor-responsive promoter element, E17. Highly selective E17-mediated reporter gene expression at pathogen infection sites in transgenic Arabidopsis thaliana plants demonstrated the potential of this promoter element for designing new strategies in resistance breeding as well as for further analysis of the early components of defense-related gene activation mechanisms. The protein encoded by the ELI17 gene exhibits various structural characteristics of established transcription factors and is designated as a CMPG protein according to the first four strictly conserved amino acids defining a newly emerging class of plant-specific proteins.