Kian Win Ong

Ajax-based report pages as incrementally rendered views

While Ajax-based programming enables faster performance and higher interface quality over pure server-side programming, it is demanding and error prone as each action that partially updates the page requires custom, ad-hoc code. The problem is exacerbated by distributed programming between the browser and server, where the developer uses JavaScript to access the page state and Java/SQL for the database. The FORWARD framework simplifies the development of Ajax pages by treating them as rendered views, where the developer declares a view using an extension of SQL and page units, which map to the view and render the data in the browser. Such a declarative approach leads to significantly less code, as the framework automatically solves performance optimization problems that the developer would otherwise hand-code. Since pages are fueled by views, FORWARD leverages years of database research on incremental view maintenance by creating optimization techniques appropriately extended for the needs of pages (nesting, variability, ordering), thereby achieving performance comparable to hand-coded JavaScript/Java applications.

Utilizing IDs to Accelerate Incremental View Maintenance

Prior Incremental View Maintenance (IVM) algorithms specify the view tuples that need to be modified by computing diff sets, which we call tuple-based diffs since a diff set contains one diff tuple for each to-be-modified view tuple. idIVM assumes the base tables have keys and performs IVM by computing ID-based diff sets that compactly identify the to-be-modified tuples through their IDs. This work makes the following contributions: (a) An ID-based IVM system for a large subset of SQL that includes the algebraic operators selection, join, grouping and aggregation, generalized projection involving functions, antisemijoin (and therefore negation/difference) and union. The system is based on a modular approach, allowing one to extend the supported language simply by adding one algebraic operator at-a-time, along with equations describing how ID-based changes are propagated through the operator. (b) An efficient algorithm that creates an IVM plan for a given view in four passes that are polynomial in the size of the view expression. (c) A formal analysis comparing the ID-based IVM algorithm to prior IVM approaches and analytically showing when one outperforms the other. (d) An experimental comparison of the ID-based IVM algorithm to prior IVM algorithms showing the superiority of the former in common use cases.

Indexing XML documents for XPath query processing in external memory

Existing encoding schemes and index structures proposed for XML query processing primarily target the containment relationship, specifically the parent-child and ancestor-descendant relationship. The presence of preceding-sibling and following-sibling location steps in the XPath specification, which is the de facto query language for XML, makes the horizontal navigation, besides the vertical navigation, among nodes of XML documents a necessity for efficient evaluation of XML queries. Our work enhances the existing range-based and prefix-based encoding schemes such that all structural relationships between XML nodes can be determined from their codes alone. Furthermore, an external-memory index structure based on the traditional B+-tree, XL+-tree(XML Location+-tree), is introduced to index element sets such that all defined location steps in the XPath language, vertical and horizontal, top-down and bottom-up, can be processed efficiently. The XL+-trees under the range or prefix encoding scheme actually share the same structure; but various search operations upon them may be slightly different as a result of the richer information provided by the prefix encoding scheme. Finally, experiments are conducted to validate the efficiency of the XL+-tree approach. We compare the query performance of XL+-tree with that of R-tree, which is capable of handling comprehensive XPath location steps and has been empirically shown to outperform other indexing approaches.

Enabling structural summaries for efficient update and workload adaptation

To facilitate queries over semi-structured data, various structural summaries have been proposed. Structural summaries are derived directly from data and serve as the indexes for evaluating path expressions. We introduce D(k)-index, an adaptive structural summary, for general graph-structured data. Building on previous 1-index and A(k)-index, D(k)-index is also based on the concept of bisimilarity. However, as a generalization of 1-index and A(k)-index, D(k)-index possesses the adaptive ability to adjust its structure to changes in query load. It also enables efficient update algorithms, which are crucial to real applications but have not been adequately addressed in previous literatures. Our experiments show that D(k)-index is a more effective structural summary than previous static ones as a result of its query load sensitivity. In addition, the update operations on it can be performed more efficient than on its predecessors.

Indexing graph-structured XML data for efficient structural join operation

Structural join has been established as a primitive technique for matching the binary containment pattern, specifically the parent-child and ancestor-descendant relationship, on the tree XML data. While current indexing approaches and evaluation algorithms proposed for the structural join operation assume the tree-structured data model, the presence of reference links in XML documents may render the underlying model a graph instead. In the more general category of semi-structured data, of which XML is an example, the data model is also usually supposed to be of graph structure. In this paper, we present an indexing approach and corresponding evaluation algorithms for efficiently performing the structural join operation on graph-structured data. Our approach encodes the structural containment relationship of a graph on multiple nested tree-structured layers, probably with the exception of the last one. With each tree-structured layer indexed with the inverted technique, the structural join operation on a graph can therefore be accomplished through recursively performing structural joins on nested layer trees. Our extensive experiments on both benchmark and synthetic XML data indicate that our proposed approach has good potential to perform significantly better than existing ones in term of both the I/O and CPU cost.

Forward: data-centric UIS using declarative templates that efficiently wrap third-party JavaScript components

While Ajax programming and the plethora of JavaScript component libraries enable high-quality Uls in web applications, integrating them with page data is laborious and error-prone as a developer has to handcode incremental modifications with trigger-based programming and manual coordination of data dependencies. The FORWARD web framework simplifies the development of Ajax applications through declarative, state-based templates. This declarative, data-centric approach is characterized by the principle of logical/physical independence, which the database community has often deployed successfully. It enables FORWARD to leverage database techniques, such as incremental view maintenance, updatable views, capability-based component wrappers and cost-based optimization to automate efficient live visualizations. We demonstrate an end-to-end system implementation, including a web-based IDE (itself built in FORWARD), academic and commercial applications built in FORWARD and a wide variety of JavaScript components supported by the declarative templates.