News recommendation aims to alleviate the big explosion of news information and helps users find their interesting news. Existing news recommendation models model users' historical click news as users' interests. Although they have achieved acceptable recommendation accuracy, they suffer from severe data sparse problems because of the limited news clicked by users. Further, the user's historical click sequence information has different effects on the user's interest, and simply combining them can not reflect this difference. Therefore, we propose an attention-based graph neural network news recommendation model. In our model, muti-channel convolutional neural network is used to generate news representations, and recurrent neural network is used to extract the news sequence information that users clicked on. Users, news, and topics are modeled as three types of nodes in a heterogeneous graph, and their relationships are modeled as edges. Graph neural network is used to effectively extract the structural information from heterogeneous graph, and helps to solve the problem of sparse data. Taking into account the different effects of different information on recommendation results, we use the attention mechanism to fuse this information distinctively. Extensive experiments conducted on the real online news datasets show that our model is superior to advanced deep learning-based recommendation methods.

The recent growth experimented by the Internet has fostered the interaction of many heterogeneous technologies under a common environment (i.e., the Internet of Things). Smart Grids entail a sound example of such situation where several devices from different vendors, running different protocols and policies, are integrated in order to reach a common goal: bring together energy delivery and smart services. Latest advances on this domain have led to effective architectures that support this idea from a technical perspective, but fail at providing powerful tools to assist this new business model. Hence, the purpose of this paper is to present a novel unified and ubiquitous management interface, driven by an intelligent system, that uses the advantages featured by the Web of Things to manage the Smart Grid. Therefore, this work opens a new path between the Internet of Things and the Web of Things resulting in a new concept coined as the Web of Energy.

Smart grids are typically built by means of several techniques and technologies concerning poorly correlated research disciplines. Up to now, practitioners have decomposed the Smart Grid problem according to each knowledge domain, and, thus, some partial solutions have been presented so far. However, these proposals are often difficult to integrate between each other and with existing platforms due to the fact that they do not consider the Smart Grid as a whole. The purpose of this paper is to propose a simple and complete secured QoS-aware ICT architecture with self-management capabilities, provided by a cognitive system, to meet the requirements of Smart Grids. Presented experimentations show the feasibility of our solution and encourage practitioners to focus their efforts in this direction.

The limited scalability of cluster-based databases has motivated a new class of storage systems based on the cloud paradigm, which favor availability over data consistency to provide highly elastic and scalable services. This paper presents a distributed storage architecture that combines a cloud inspired scheme with traditional database replication concepts to provide transactional support as well as high availability by offering different consistency levels according to the demands of client applications, thanks to a replication strategy based on epidemic updates. We also include an analytical model for computing the scale out of a distributed system that can be used for adjusting the configuration of the proposed architecture.

Database clusters based on share-nothing replication techniques are currently widely accepted as a practical solution to scalability and availability of the data tier. A key issue when planning such systems is the ability to meet service level agreements when load spikes occur or cluster nodes fail. This translates into the ability to provision and deploy additional nodes. Many current research efforts focus on designing autonomic controllers to perform such reconfiguration, tuned to quickly react to system changes and spawn new replicas based on resource usage and performance measurements. In contrast, we are concerned about the inherent impact of deploying an additional node to an online cluster, considering both the time required to finish such an action as well as the impact on resource usage and performance of the cluster as a whole. If noticeable, such impact hinders the practicability of self-management techniques, since it adds an additional dimension that has to be accounted for. Our approach is to systematically benchmark a number of different reconfiguration scenarios to assess the cost of bringing a new replica online. We consider factors such as: workload characteristics, incremental and parallel recovery, flow control and outdatedness of the recovering replica. As a result, we show that research should be refocused from optimizing the capture and transmition of changes to applying them, which in a realistic setting dominates the cost of the recovery operation.

Database replication is widely used for fault tolerance and performance. However, it requires replica control to keep data copies consistent despite updates. The traditional correctness criterion for the concurrent execution of transactions in a replicated database is 1-copy-serializability. It is based on serializability, the strongest isolation level in a nonreplicated system. In recent years, however, Snapshot Isolation (SI), a slightly weaker isolation level, has become popular in commercial database systems. There exist already several replica control protocols that provide SI in a replicated system. However, most of the correctness reasoning for these protocols has been rather informal. Additionally, most of the work so far ignores the issue of integrity constraints. In this article, we provide a formal definition of 1-copy-SI using and extending a well-established definition of SI in a nonreplicated system. Our definition considers integrity constraints in a way that conforms to the way integrity constraints are handled in commercial systems. We discuss a set of necessary and sufficient conditions for a replicated history to be producible under 1-copy-SI. This makes our formalism a convenient tool to prove the correctness of replica control algorithms.

Database replication protocols based on a certification approach are usually the best ones for achieving good performance. The weak voting approach achieves a slightly longer transaction completion time, but with a lower abortion rate. So, both techniques can be considered as the best ones for replication when performance is a must, and both of them take advantage of the properties provided by atomic broadcast. We propose a new database replication strategy that shares many characteristics with such previous strategies. It is also based on totally ordering the application of writesets, using only an unordered reliable broadcast, instead of an atomic broadcast. Additionally, the writesets of transactions that are aborted in the final validation phase are not broadcast in our strategy. Thus, this new approach reduces the communication traffic and also achieves a good transaction response time (even shorter than those previous strategies in some system configurations).

The virtually synchronous execution model provides anappropriate support for developing reliable applications when the crash failure model is being assumed. Using it, group broadcasts only need to be based on asynchronous communication. Synchronization points are set when a view change arises, guaranteeing an efficient execution of such reliable applications. But a crash failure model is not always appropriate for all applications. Indeed, those using persistent or large state, like replicated databases, need a recoverable model. In such cases, the virtual synchrony property needs to be partially extended for adequately supporting more intricate recovery protocols. Persistent logical synchrony is one variation of this kind, that extends the synchronization actions to be taken when aview change arises, allowing a good support for partial recovery when the primary component membership is being assumed.

In this work, we present the correctness criteria that ensures a replicated database behaves like a single copy where trans-actions see a weaker form of SI, called Generalized-SI, with deferred update protocols in a crash failure scenario.

Middleware database replication is a way to increase availability and afford site failures for dynamic content Websites. There are several replication protocols that ensure data consistency for these systems. The most attractive ones are those providing generalized snapshot isolation (GSI), as read operations never block. These replication protocols are based on the certification process, however, up to our knowledge, they do not cope with the recovery of a replica. In this paper we propose a recovery protocol that ensures GSI (we provide an outline of its correctness) that does not interfere with user transactions and permits the execution of transactions in the recovering node, even though the recovery process has not finished

Mobile databases are a centerpiece of the dramatic growth of data-centric applications for mobile computing, nomadic communication and wireless networks. Replication of database content is useful in client-server and peer- to-peer configurations of mobile distributed databases. We present an adaptation of generalized snapshot isolation for transactions on content data in mobile networks. This solution overcomes various limitations of known approaches to manage mobile database transactions.

Middleware database replication techniques is a way to increase performance and fault tolerance without modifying the database management system (DBMS) internals. However, it introduces an additional overhead that may lead to poor response times. In this paper we present a modification of the optimistic two phase locking (O2PL) M.J. Carey et al. (1991) protocol that orders transactions by way of a deadlock prevention schema, instead of using the total order transaction delivery obtained by group communication systems (GCSs) G. Chockler et al. (2001) techniques, and do not need the 2 phase commit (2PC) rule P.A. Bernstein et al. (1987). We formalize its definition as a state transition system and show that it is 1-copy-serializable (1CS) P.A. Bernstein et al. (1987).

Database replication protocols need to detect, block or abort part of conflicting transactions. A possible solution is to check their writesets (and also their readsets in case a serialisable isolation level is requested), which however burdens the consumption of CPU time. This gets even worse when the replication support is provided by a middleware, since there is no direct DBMS support in that layer. We propose and discuss the use of the concurrency control support of the local DBMS for detecting conflicts between local transactions and writesets of remote transactions. This allows to simplify many database replication protocols and to enhance their performance