Large events with many attendees cause congestion in the traffic network around the venue. To avoid accidents or delays due to this kind of unexpected congestion, it is important to predict the level of congestion in advance of the event. This study aimed to forecast congestion triggered by large events. However, historical congestion information alone is insufficient to forecast congestion at large venues when non-recurrent events are held there. To address this problem, we utilize microblog posts that refer to future events as an indicator of event attendance. We propose a regression model that is trained with microblog posts and historical congestion information to accurately forecast congestion at large venues. Experiments on next 24-hour congestion forecasting using real-world traffic and Twitter data demonstrate that our model reduces the prediction errors over those of the baseline models (autoregressive and long short term memory) by 20% - 50%.

A temporal database is a collection of transactions, ordered by their timestamps. Discovering partial periodic itemsets in temporal databases has numerous applications. However, to the best of our knowledge, no work has considered finding these itemsets in temporal databases, despite that this type of data is very common in real-life. Discovering partial periodic itemsets in temporal databases is challenging. It requires defining (i) an appropriate measure to assess the periodic interestingness of itemsets, and (ii) an algorithm to efficiently find all partial periodic itemsets. While a pattern-growth algorithm can be employed for the second sub-task, the first sub-task has not been addressed. Moreover, how these two tasks are combined has significant implications. In this paper, we address this challenge. We introduce a model to find partial periodic itemsets in temporal databases. A new measure, called periodic-frequency, has been proposed to determine the periodic interestingness of itemsets by taking into account their number of cyclic repetitions in the entire data. Moreover, the paper introduces a pattern-growth algorithm to discover all partial periodic itemsets. Experimental results demonstrate that our model is efficient.

The development of cloud storage and computing has facilitated the rise of various big data applications. As a representative high performance computing (HPC) workload, graph processing is becoming a part of cloud computing. However, scalable computing on large graphs is still dominated by HPC solutions, which require high performance all-to-all collective operations over torus (or mesh) networking. Implementing those torus-based algorithms on commodity clusters, e.g., cloud computing infrastructures, can result in great latency due to inefficient communication. Moreover, designing a highly scalable system for large social graphs, is far from being trivial, as intrinsic features of social graphs, e.g., degree skewness and lacking of locality, often profoundly limit the extent of parallelism.

Partial periodic patterns are an important class of regularities that exist in a time series. A key property of these patterns is that they can start, stop, and restart anywhere within a series. We classify partial periodic patterns into two types: (i) regular patterns−patterns exhibiting periodic behavior throughout a series with some exceptions and (ii) recurring patterns−patterns exhibiting periodic behavior only for particular time intervals within a series. Past studies on partial periodic search have been primarily focused on finding regular patterns. One cannot ignore the knowledge pertaining to recurring patterns. This is because they provide useful information pertaining to seasonal or temporal associations between events. Finding recurring patterns is a non-trivial task because of two main reasons. (i) Each recurring pattern is associated with temporal information pertaining to its durations of periodic appearances in a series. Obtaining this information is challenging because the information can vary within and across patterns. (ii) Finding all recurring patterns is a computationally expensive process since they do not satisfy the anti-monotonic property. In this paper, we propose recurring pattern model by addressing the above issues. We also propose Recurring Pattern growth algorithm along with an efficient pruning technique to discover these patterns. Experimental results show that recurring patterns can be useful and that our algorithm is efficient.

Provenance is a record that describes entities and processes involved in producing, delivering and influencing a resource. Provenance management and reuse can enable interesting applications for knowledge discovery and analytics. One crucial component of a provenance management system is the comparison between provenances. In the era of big data, provenance management systems are in need of a scalable algorithmic solution for efficient comparison. Existing solutions to the problem have large memory footprint and require overlong system response time. In this paper, we present a new solution to threshold-based provenance comparison. We model provenance directly as graph, and propose to measure provenance similarity using provenance edit distance. Following the depth-first search paradigm, we design an algorithm PEDSim based on an encoding technique specific to provenance graphs and quantifiable heuristics. Extensive experiments on real data demonstrate the superiority of our method to other alternatives.

Many recent large-scale data intensive applications are increasingly demanding efficient graph databases. Distributed graph algorithms, as a core part of practical graph databases, have a wide range of important applications, but have been rarely studied in sufficient detail. These problems are challenging as real graphs are usually extremely large and the intrinsic character of graph data, lacking locality, causes unbalanced computation and communication workloads.

Finding the skyline in a multi-dimensional space is relevant to a wide range of applications. The skyline operator over a set of d -dimensional points selects the points that are not dominated by any other point on all dimensions. Therefore, it provides a minimal set of candidates for the users to make their personal trade-off among all optimal solutions. The existing algorithms establish both the worst case complexity by discarding distributions and the average case complexity by assuming dimensional independence. However, the data in the real world is more likely to be anti-correlated. The cardinality and complexity analysis on dimensionally independent data is meaningless when dealing with anti-correlated data. Furthermore, the performance of the existing algorithms becomes impractical on anti-correlated data. In this paper, we establish a cardinality model for anti-correlated distributions. We propose an accurate polynomial estimation for the expected value of the skyline cardinality. Because the high skyline cardinality downgrades the performance of most existing algorithms on anti-correlated data, we further develop a determination and elimination framework which extends the well-adopted elimination strategy. It achieves remarkable effectiveness and efficiency. The comprehensive experiments on both real datasets and benchmark synthetic datasets demonstrate that our approach significantly outperforms the state-of-the-art algorithms under a wide range of settings.

A supergraph containment search is to retrieve the data graphs contained by a query graph. In this paper, we study the problem of efficiently retrieving all data graphs approximately contained by a query graph, namely similarity search on supergraph containment. We propose a novel and efficient index to boost the efficiency of query processing. We have studied the query processing cost and propose two index construction strategies aimed at optimizing the performance of different types of data graphs: top-down strategy and bottom-up strategy. Moreover, a novel indexing technique is proposed by effectively merging the indexes of individual data graphs; this not only reduces the index size but also further reduces the query processing time. We conduct extensive experiments on real data sets to demonstrate the efficiency and the effectiveness of our techniques.

Substructure similarity search is to retrieve graphs that approximately contain a given query graph. It has many applications, e.g., detecting similar functions among chemical compounds. The problem is challenging as even testing subgraph containment between two graphs is NP-complete. Hence, existing techniques adopt the filtering-and-verification framework with the focus on developing effective and efficient techniques to remove non-promising graphs.

Similarity join is a useful primitive operation underlying many applications, such as near duplicate Web page detection, data integration, and pattern recognition. Traditional similarity joins require a user to specify a similarity threshold. In this paper, we study a variant of the similarity join, termed top-k set similarity join. It returns the top-k pairs of records ranked by their similarities, thus eliminating the guess work users have to perform when the similarity threshold is unknown before hand. An algorithm, topk-join, is proposed to answer top-k similarity join efficiently. It is based on the prefix filtering principle and employs tight upper bounding of similarity values of unseen pairs. Experimental results demonstrate the efficiency of the proposed algorithm on large-scale real datasets.

Graphs are widely used to model complicated data semantics in many applications. In this paper, we aim to develop efficient techniques to retrieve graphs, containing a given query graph, from a large set of graphs. Considering the problem of testing subgraph isomorphism is generally NP-hard, most of the existing techniques are based on the framework of filtering -and- verification to reduce the precise computation costs; consequently various novel feature-based indexes have been developed. While the existing techniques work well for small query graphs, the verification phase becomes a bottleneck when the query graph size increases. Motivated by this, in the paper we firstly propose a novel and efficient algorithm for testing subgraph isomorphism, QuickSI. Secondly, we develop a new feature-based index technique to accommodate QuickSI in the filtering phase. Our extensive experiments on real and synthetic data demonstrate the efficiency and scalability of the proposed techniques, which significantly improve the existing techniques.