Populating ontology graphs represents a long-standing problem for the Semantic Web community. Recent advances in translation-based graph embedding methods for populating instance-level knowledge graphs lead to promising new approaching for the ontology population problem. However, unlike instance-level graphs, the majority of relation facts in ontology graphs come with comprehensive semantic relations, which often include the properties of transitivity and symmetry, as well as hierarchical relations. These comprehensive relations are often too complex for existing graph embedding methods, and direct application of such methods is not feasible. Hence, we propose On2Vec, a novel translation-based graph embedding method for ontology population. On2Vec integrates two model components that effectively characterize comprehensive relation facts in ontology graphs. The first is the Component-specific Model that encodes concepts and relations into low-dimensional embedding spaces without a loss of relational properties; the second is the Hierarchy Model that performs focused learning of hierarchical relation facts. Experiments on several well-known ontology graphs demonstrate the promising capabilities of On2Vec in predicting and verifying new relation facts. These promising results also make possible significant improvements in related methods.

Latent Dirichlet Allocation (LDA) is an extremely popular probabilistic topic model used for a diverse class of appications. While highly effective, one important limitation of LDA is the high memory footprint of its inferencing algorithm, making it difficult to scale to a large dataset. In my thesis, I propose sdLDA, a highly-scalable disk-based LDA that (1) leverages the plentiful space available in disk to reduce its main-memory footprint and (2) preserves the sparsity of the extracted topics during sampling to improve both memory efficiency and sampling complexity of the inferencing algorithm. Our extensive experiments show that sdLDA scales to datasets that are two orders of magnitude larger than what existing main-memory-based algorithms can handle. Furthermore, sdLDA exhibits similar (or even better) performance compared to main-memory-based LDAs in terms of running time.

Recently, lots of micro-blog message sharing applications have emerged on the web. Users can publish short messages freely and get notified by the subscriptions instantly. Prominent examples include Twitter, Facebook's statuses, and Sina Weibo in China. The Micro-blog platform becomes a useful service for real time information creation and propagation. However, these messages' short length and dynamic characters have posed great challenges for effective content understanding. Additionally, the noise and fragments make it difficult to discover the temporal propagation trail to explore development of micro-blog messages. In this paper, we propose a provenance model to capture connections between micro-blog messages. Provenance refers to data origin identification and transformation logging, demonstrating of great value in recent database and workflow systems. To cope with the real time micro-message deluge, we utilize a novel message grouping approach to encode and maintain the provenance information. Furthermore, we adopt a summary index and several adaptive pruning strategies to implement efficient provenance updating. Based on the index, our provenance solution can support rich query retrieval and intuitive message tracking for effective message organization. Experiments conducted on a real dataset verify the effectiveness and efficiency of our approach. Provenance refers to data origin identification and transformation monitoring, which has been demonstrated of great value in database and workflow systems. In this paper, we propose a provenance model in micro-blog platforms, and design an indexing scheme to support provenance-based message discovery and maintenance, which can capture the interactions of messages for effective message organization. To cope with the real time micro-message tornadoes, we introduce a novel virtual annotation grouping approach to encode and maintain the provenance information. Furthermore, we design a summary index and adaptive pruning strategies to facilitate efficient message update. Based on this provenance index, our approach can support query and message tracking in micro-blog systems. Experiments conducted on real datasets verify the effectiveness and efficiency of our approach.

Recent years have witnessed the flourishing increases of micro-blog message applications. Prominent examples include Twitter, Facebook's status, and Sina Weibo in China. Messages in these applications are short (140 characters in a message) and easy to create. The subscription and re-sharing features also make it fairly intuitive to propagate. Micro-blog applications provide abundant information to present world scale user interests and social pulse in an unexpected way. But the precious corpus also brings out the noise and fast changing fragments to prohibit effective understanding and management.