A Transaction Model for Executions of Compositions of Internet of Things Services

AbstractInternet of Things (IoT) is about making “things” smart in some functionality, and connecting and enabling them to perform complex tasks by themselves. The functionality can be encapsulated as services and the task executed by composing the services. Two noteworthy functionalities of IoT services are monitoring and actuation. Monitoring implies continuous executions, and actuation is by triggering. Continuous executions typically involve stream processing. Stream input data are accumulated into batches and each batch is subjected to a sequence of computations, structured as a dataflow graph. The composition may be processing several batches simultaneously. Additionally, some non-stream OLTP transactions may also be executing concurrently. Thus, several composite transactions may be executing concurrently. This is in contrast to a typical Web services composition, where just one composite transaction is executed on each invocation. Therefore, defining transactional properties for executions of IoT service compositions is much more complex than for those of conventional Web service compositions. In this paper, we propose a transaction model and a correctness criterion for executions of IoT service compositions. Our proposal defines relaxed atomicity and isolation properties for transactions in a flexible manner and can be adapted for a variety of IoT applications

On Atomic Batch Executions in Stream Processing

AbstractStream processing is about processing continuous streams of data by programs in a workflow. Continuous execution is discretized by grouping input stream tuples into batches and using one batch at a time for the execution of programs. As source input batches arrive continuously, several batches may be processed in the workflow simultaneously. A general requirement is that each batch be processed completely in the workflow. That is, all the programs triggered by the batch, directly and transitively, in the workflow must be executed successfully. Executing only a prefix of the workflow amounts to dropping (discarding) the batches that were derived by the executed part and were supposed to be input to the rest of the workflow. In some cases, such partial executions may not be acceptable and may have to be rolled back, amounting to dropping the source input batches that were processed by the partial execution. We refer to this property of processing the batches either completely or not at all as atomic execution of the batches. We also attribute the property to the batches themselves, calling them atomic batches, meaning that the property applies to the set of transactions that are executed due to that batch. If batches are processed in isolation in the workflow, preserving atomicity is fairly straightforward. When batches are split or merged along the workflow computation, the problem becomes complicated. In this paper, we study issues relating to the atomicity of batches. We illustrate that, in general, preserving atomicity of some batches may affect the atomicity of some other batches, and suggest trade-offs

Capability-based resiliency control of distributed database systems

It is highly desirable for a distributed database system to achieve logically continuous operation even if some sites or message links fail. In this paper, we describe a scheme that can automati­cally reconfigure a fully-replicated distributed database system upon subsystem failures. The scheme can tolerate total failures of some sites. That is, some sites may lose their data completely including backup data. In order to handle this problem, we divide the execution of the system into generations. Each generation starts with a consistent database state and ends with a consistent database state. Serial­izability of the execution of each generation is enforced by con­currency control based on conditional capabilities. Conditional capabilities are valid only if they are being endorsed by a majority of sites in the system. Thus, any majority set of sites can invali­date lost or stray capabilities of old generations, and they can newly create capabilities for a new generation. Therefore, as long as there exist a majority of working sites that belong to the same partition, the system can continue its operation. The scheme allows a system to be reconfigured even if some transactions are being pro­cessed and even if other system reconfiguration attempts are under­way.Key Words and Phrases: distributed database system, resiliency con­trol, consistent database state, replicated data, conditional capa­bilitie

Electrochemically synthesized polymers in molecular imprinting for chemical sensing

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered

Selective Molecular Recognition in Imprinted Polymeric Adsorbents and in Biological Macromolecules

This thesis describes the synthesis and use of molecularly imprinted polymeric adsorbents for use in ligand-exchange chromatographic separations of structurally similar substrates. A general model of stereo selectivity is also described, which can be applied both to chromatographic adsorbents and to biological receptors. Crosslinking polymerization of trimethylolpropane trimethacrylate (TRIM), under controlled conditions yields macroporous polymers bearing surface-accessible unpolymerized methacrylate residues. These residues have been utilized for copolymerization with different functional monomers to obtain composite polymer matrices with surface coatings of functional polymer chains. Surface modification has been carried out by molecular imprinting, using ternary Cu^(2+) complexes of [N-(4-vinylbenzyl)imino]diacetate and bisimidazole templates, with ethylene glycol dimethacrylate as comonomer. Selectivity characteristics similar to bulk-copolymerized polymers have been observed. The physicochemical characteristics of these functional polymer matrices have been evaluated by ^(13)C NMR, X-ray photoelectron spectroscopy, IR spectroscopy, and scanning electron microscopy. The ability of molecular imprinting to impart enantioselectivity to polymeric adsorbents has been studied using Cu^(2+) complexes of the achiral monomer [N-(4-vinylbenzyl)imino]diacetate and α-amino acids. Crosslinking polymerization with ethylene glycol dimethacrylate as the comonomer yields polymeric adsorbents capable of enantioresolutions of underivatized α-amino acids. Chromatographic adsorbents have been prepared by grafting the imprinted polymer on to silica particles. The observed enantioselectivity increases corresponding to the size of the side chain of the amino acid used as template, with the best enantioresolutions being obtained for materials imprinted against phenylalanine (~1.65 for D,L-phenylalanine enantioresolution). Adsorbents imprinted for alanine show negligible enantioselectivity. Cross-selectivity patterns towards non-template amino acids have been investigated, and the ability of an amino acid imprinted material to resolve analogous chiral amines has been demonstrated. The mechanisms underlying enantioselectivity in imprinted polymers are discussed in terms of the three-point interaction model. This model has been extended to a stereocenter-recognition (SR) model for substrates with multiple stereocenters. For N stereocenters in a linear chain, it has been demonstrated that a minimum of N + 2 interactions need to be distributed over all stereocenters, such that three effective interactions exist per stereocenter. The general applicability of the SR model is demonstrated for biological ligand-receptor interactions, by reinterpreting several previous experimental observations.</p