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An XML publish/subscribe system needs to filter a large number of queries over XML streams. Most existing systems only consider filtering the simple XPath statements. In this paper, we focus on filtering of the more complex generalized-tree-pattern (GTP) queries. Our filtering mechanism is based on a novel Tree-of-Path (TOP) encoding scheme, which compactly represents the path matches for the entire document. First, we show that the TOP encodings can be efficiently produced via a shared bottom-up path matching. Second, with the aid of this TOP encoding, we can (1) achieve polynomial time and space complexity for post processing, (2) avoid redundant predicate evaluations, (3) allow an efficient duplicate-free and merge join-based algorithm for merging multiple encoded path matches and (4) simplify the processing of GTP queries. Overall our approach maximizes the sharing opportunity across queries by exploiting the suffix as well as prefix sharing. At the same time, our TOP encodings allow efficient post processing for GTP queries. Extensive performance studies show that our GFilter solution not only achieves significantly better filtering performance than state-of-the-art algorithms, but also is capable of efficiently filtering the more complex GTP queries.

Summarization of hierarchical data and metadata is a fundamental operation in applications in many domains. In particular, similarity search of hierarchical data, such as XML, would benefit greatly from concise and indexable summaries. This is especially true in P2P scenarios, where the search needs to be done in a distributed fashion on multiple peers. This situation requires summaries which are small, yet effective in identifying potential peers that need to be further explored. In this paper, we propose a method, called propagation-vectors for trees (PVT) which constructs very concise and accurate summaries of hierarchical data, such as XML trees. We then show how to use this summary to perform similarity search on summarized data. The proposed summarization scheme relies on a label-propagation mechanism, which constructs an n-dimensional vector from a given tree with n unique data labels. Experimental results have shown that the constructed PVT summaries capture the structure of the input trees very accurately, the representations are highly concise, and that the search based on these summaries are faster than the existing approaches.

Basic message processing tasks, such as well-formedness checking and grammar validation, can be off-loaded from the service providers' own infrastructures. To enable effective off-loading of processing tasks, we introduce the Prefix Automata SyStem - PASS, a middleware architecture which distributively processes XML payloads of Web service SOAP messages during their routing towards Web servers. PASS is based on a network of automata, where PASS-nodes independently but cooperatively process parts of the SOAP message XML payload.