Period Optimization for Hard Real-time Distributed Automotive Systems
The complexity and physical distribution of modern active-safety automotive applications requires the use of distributed architectures. These architectures consist of multiple electronic control units (ECUs) connected with standardized buses. The most common configuration features periodic activation of tasks and messages coupled with run-time priority-based scheduling. The correct deployment of applications on such architectures requires end-to- end latency deadlines to be met. This is challenging since deadlines must be enforced across a set of ECUs and buses, each of which supports multiple functionality. The need for accommodating legacy tasks and messages further complicates the scenario. In this work, we automatically assign task and message periods for distributed automotive systems. This is accomplished by leveraging schedulability analysis within a convex optimization framework to simultaneously assign periods and satisfy end-to-end latency constraints. Our approach is applied to an industrial case study as well as an example taken from the literature and is shown to be both effective and efficient.

title: Efficient octilinear steiner tree construction based on spanning graphs
abstract: Octilinear interconnect is a promising technique to shorten wire lengths. We present two practical heuristic octilinear Steiner tree (OSMT) algorithms in the paper. They are both based on octilinear spanning graphs. The one by edge substitution (OST-E) has a worst case running time of O(nlogn) and similar performance as the batched greedy algorithm[9]. The other one by triangle contraction (OST-T) has a small increase in running time and better performance. Experiments on both industry and random test cases are conducted.

title: Optimizing complex queries based on similarities of subqueries
abstract: As database technology is applied to more and more application domains, user queries are becoming increasingly complex (e.g. involving a large number of joins and a complex query structure). Query optimizers in existing database management systems (DBMS) were not developed for efficiently processing such queries and often suffer from problems such as intolerably long optimization time and poor optimization results. To tackle this challenge, we present a new similarity-based approach to optimizing complex queries in this paper. The key idea is to identify similar subqueries that often appear in a complex query and share the optimization result among similar subqueries in the query. Different levels of similarity for subqueries are introduced. Efficient algorithms to identify similar queries in a given query and optimize the query based on similarity are presented. Related issues, such as choosing good starting nodes in a query graph, evaluating identified similar subqueries and analyzing algorithm complexities, are discussed. Our experimental results demonstrate that the proposed similarity-based approach is quite promising in optimizing complex queries with similar subqueries in a DBMS.

title: Multimodal fusion using learned text concepts for image categorization
abstract: Conventional image categorization techniques primarily rely on low-level visual cues. In this paper, we describe a multimodal fusion scheme which improves the image classification accuracy by incorporating the information derived from the embedded texts detected in the image under classification. Specific to each image category, a text concept is first learned from a set of labeled texts in images of the target category using Multiple Instance Learning . For an image under classification which contains multiple detected text lines, we calculate a weighted Euclidian distance between each text line and the learned text concept of the target category. Subsequently, the minimum distance, along with low-level visual cues, are jointly used as the features for SVM-based classification. Experiments on a challenging image database demonstrate that the proposed fusion framework achieves a higher accuracy than the state-of-art methods for image classification.

title: Evolutionary techniques for updating query cost models in a dynamic multidatabase environment
abstract: Deriving local cost models for query optimization in a dynamic multidatabase system (MDBS) is a challenging issue. In this paper, we study how to evolve a query cost model to capture a slowly-changing dynamic MDBS environment so that the cost model is kept up-to-date all the time. Two novel evolutionary techniques, i.e., the shifting method and the block-moving method, are proposed. The former updates a cost model by taking up-to-date information from a new sample query into consideration at each step, while the latter considers a block (batch) of new sample queries at each step. The relevant issues, including derivation of recurrence updating formulas, development of efficient algorithms, analysis and comparison of complexities, and design of an integrated scheme to apply the two methods adaptively, are studied. Our theoretical and experimental results demonstrate that the proposed techniques are quite promising in maintaining accurate cost models efficiently for a slowly changing dynamic MDBS environment. Besides the application to MDBSs, the proposed techniques can also be applied to the automatic maintenance of cost models in self-managing database systems.

title: Optimizing large star-schema queries with snowflakes via heuristic-based query rewriting
abstract: User queries have been becoming increasingly complex (e.g., involving a large number of joins) as database technology is applied to some application domains such as data warehouses and life sciences. Query optimizers in existing database management systems often suffer from intolerably long optimization time and/or poor optimization results when optimizing large join queries. One possible solution to tackle these problems is to rewrite a user-specified complex query into another form that can better utilize the capability of the underlying query optimizer, based on some heuristic rules, before sending the query to the next query optimization stage. We focus on studying a special type of complex query possessing a star-schema structure with snowflakes, simply called the snow-schema query. The key idea is to split a given snow-schema query into several levels of small query blocks at the query rewriting stage. The query optimizer then optimizes the query blocks and integrates their results into the final query result. A set of heuristic rules on how to divide the query is introduced. A query rewriting framework adopting these heuristics is presented. Experimental results demonstrate that this heuristic-based query rewriting technique is quite promising in optimizing large snow-schema queries.

title: Global Query Optimization Based on Multistate Cost Models for a Dynamic Multidatabase System
abstract: Global query optimization in a multidatabase system (MDBS) is a challenging issue since some local optimization information such as local cost models may not be available at the global level due to local autonomy. It becomes even more difficult when dynamic environmental factors are taken into consideration. In our previous work, a qualitative approach was suggested to build so-called multistate cost models to capture the performance behavior of a dynamic multidatabase environment. It has been shown that a multistate cost model can give a good cost estimate for a query run in any contention state in the dynamic environment. In this paper, we present a technique to perform query optimization based on multistate cost models for a dynamic MDBS. Two relevant algorithms are proposed. The first one selects a set of representative system environmental states for generating an execution plan with multiple versions for a given query at compile time, while the second one efficiently determines the best version to invoke for the query at run time. Experiments demonstrate that the proposed technique is quite promising for performing global query optimization in a dynamic MDBS. Compared with related work on dynamic query optimization, our approach has an advantage of avoiding the high overhead for modifying or re-generating an execution plan for a query based on dynamic run-time information.