Browsing by Author "Dr. Rada Chirkova, Committee Member"

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Commitment Alignment: Semantics, Patterns, and Decision Procedures for Distributed Computing
(2008-12-05) Chopra, Amit Khushwant; Dr. Rada Chirkova, Committee Member; Dr. S. Purushothaman Iyer, Committee Member; Dr. Mladen A. Vouk, Committee Member; Dr. Munindar P. Singh, Committee Chair
Current service-oriented architectures lack business-level software abstractions. As a result, service implementations are unnecessarily rigid. Commitment-Based SOA or CSOA, an agent-oriented approach to SOA, fills this gap. The key insight of CSOA is that commitments are crucial to realizing the full possibilities of engagement. In CSOA, each business service is modeled as an agent. CSOA gives primacy to the interactions among agents. Interactions have business meaning in terms of the commitments the agents have toward each other. This dissertation takes a distributed systems view of CSOA, where agents communicate using asynchronous messaging. A problem that arises in distributed settings is that of commitment misalignment: an agent comes to infer a commitment from another agent, but the other agent does not infer that commitment. A commitment misalignment precludes any possibility of successful engagement among agents. We formalize alignment under asynchronous messaging. We consider three causes of misalignments. (1) Autonomy: agents are free to send messages; in other words, they communicate asynchronously. (2) Distribution: in a distributed system, some agents would in general have more information than others. (3) Interface incompatibility: agents assign different meanings to messages. To address the first two causes, we propose a formalization of commitments that consists of three elements: a semantics of the commitment operations; messaging patterns that implement the commitment operations; and weak constraints on agents' behaviors to ensure the propagation of vital information. The constraints constitute additional messaging patterns that are critical to alignment. We prove that our formalization ensures that no misalignment arises because of autonomy and distribution. We illustrate the generality of our formalization with several real-life scenarios. To address interface incompatibility, we formulate a decision procedure that checks for interface compatibility, and prove its correctness.
Crossing Minimization in k-layer graphs
(2009-01-06) Gupta, Saurabh; Dr. Carla D. Savage, Committee Member; Dr. Matthias Stallmann, Committee Chair; Dr. Rada Chirkova, Committee Member
The crossing minimization problem in graphs has been extensively studied for the case when graphs are to be embedded on two layers. There are many well known heuristics for the 2-layer crossing minimization problem, like, for example, the barycenter and the median heuristic. The problem has not been studied much for k-layer graphs. The k-layer graph crossing minimization problem has specific application in aesthetic design of hierarchical structures, in VLSI circuit design to reduce the total wire length and crosstalk, and in various organization charts, flow diagrams and large graphs that arise in activity-based management. In our thesis work, we have extended the 2-layer graph heuristics to the crossing minimization problem for k-layer graphs. We have proposed twenty six heuristics for the k-layer graph problem. We have tested all the proposed heuristics on various classes of graphs instances including the structures that arise in activity-based management. The proposed heuristics have significantly outperformed the traditional sweep based heuristics. Additional experiments performed on the best performing heuristics have helped us to propose new enhancements on those heuristics, which have improved the performance of the heuristics further.
A Database Level Implementation To Enforce Fine Grained Access Control
(2008-05-06) Arjun, Vinod; Dr. Ting Yu, Committee Chair; Dr. Peng Ning, Committee Member; Dr. Rada Chirkova, Committee Member
As privacy protection has gained significant importance, organizations have been forced to protect individual preferences and comply with many enacted privacy laws. This has been a strong driving force for access control in relational databases. Traditional relation level access control is insufficient to address the increasingly complex requirements of access control policies where each cell in the relation might be governed by a separate policy. In order to address this demand, we are in need of a more fine grained access control scheme, at the row-level or even the cell-level. A recent research paper proposed correctness criteria for query evaluation algorithms enforcing fine grained access control and showed that existing approaches did not satisfy the criteria. In addition, the paper proposed a query modification approach to implement a sound and secure query evaluation algorithm enforcing fine grained access control. To evaluate queries involving moderate table sizes of 50000 and 100000 records we experimentally find that the implementation takes approximately 8 and 32 seconds respectively. This is approximately 10 times, on an average, slower than query evaluation algorithms without access control. This performance gap increases significantly with increase in table size, thus rendering it impractical. In this thesis, we modify the query evaluation engine of POSTGRESQL to enforce fine grained access control at the database level. We address a few challenges and propose optimizations to counter inefficiencies that we encounter when moving the access control scheme to the database level. We analyze the performance of our implementation using data sets with various properties and find that it performs approximately 10 times better compared to the query modification approach on moderate table sizes of 50000 and 100000 records. Also, we find that our implementation scales well with table size. Experimental results show that our implementation is comparable to the performance of query evaluation algorithms without access control and hence is practical.
Nonmonotonic Commitment Machines
(2003-11-07) Chopra, Amit Khushwant; Dr Munindar P. Singh, Committee Chair; Dr. Rada Chirkova, Committee Member; Dr. R. Michael Young, Committee Member
Protocols in open and dynamic multiagent systems cannot be modeled via formalisms such as finite state machines (FSMs). FSMs though formal, lack content, that is, a protocol-level semantics, which leads to rigidity in protocols. We propose formalism called Nonmonotonic Commitment Machines (NCMs) for representing protocols. An NCM gives a commitment-based semantics to actions and states in a protocol. Protocols represented as NCMs afford the agent flexibility in interactions with other agents. In particular, situations in protocols when nonmonotonic reasoning is required can be efficiently represented in NCMs. For applications that need efficient execution, we show how to compile an NCM into an FSM and prove the compilation to be sound and complete.
Optimization of the Processing in a Middleware Environment for a Set of XML Variants
(2007-03-22) Sahijwani, Vineet; Dr. Rudra Dutta, Committee Chair; Dr. Matthias F. Stallmann, Committee Member; Dr. Rada Chirkova, Committee Member
The middleware has become an important product category since the 1990s, when companies started to adopt client-server architectures and had to deal with distributed computing problems. It employs the component based design to distribute the processing across the network. The middleware components use proprietary formats or more popularly XML for data exchange. There are different formats or variants of XML available which when used can improve the processing speed at a middleware component. However it is possible that the same format may not be suitable or be the best for all the components the XML goes through. Thus from a given set of XML variants or formats, there can be a particular XML format that will process faster as compared to others in a given middleware component. That same XML format however may not be suitable for other middleware components and some other format from the set might be. In this thesis we consider the problem of improving the processing speed in the middleware, given a set of different XML formats. We propose the use of local optimization to achieve global optimization. We find the best suited XML format for each component. This is done with the help of a feedback based software monitoring system. The software collects data about the processing time taken in a particular component by different formats with the help of feedback from that component and then process that data to decide which format suits that component best. Once the formats are known, the data can be sent to the components in that format and it would result in faster processing in the system as a whole, as compared to, if a single format was used for all the components. We also numerically investigate the performance of a middleware environment with and without the feedback based software monitoring system.