@conference {
	title = {Compositional Analysis of Dynamic Bayesian Networks and Applications to Complex Dynamic System Decomposition},
	author = {Yang, Shahan., Zhou, Yuchen., Baras, John S.},
	year = {2013},
	month = {03/2013},
	abstract = {Dynamic Bayesian networks (DBNs) can be effectively used to model various problems in complex dynamic systems. We perform an empirical investigation on compositional analysis of DBNs using abstraction. In static systems and hidden Markov models, computation of a metric called treewidth induces a tree decomposition that can be used to perform logical or probabilistic inference and max + optimizations in time exponential in treewidth and linear in overall system size. Intuitively, the linear scaling means that very large systems can be analyzed as long as they are sufficiently sparse and well structured. In these simple cases, summary propagation, which uses two operations, summation (projection) and product (composition), suffices to perform the inference or optimization. Here, we begin an extension of this to structured networks of communicating dynamic systems. We define generalizations of projection and composition operators that treat labeled Markov chains as primitive objects. The projection operation, corresponding to summation, is implemented as label deletion followed by exact state reduction for Markov chains, similar to Hopcroft{\textquoteright}s DFA minimization algorithm, with O(n log m) complexity. The composition operation is the product of state machines. We use canonical MDDs, similar to BDDs, to capture logical dependencies symbolically. Combining symbolic representations with Markov chain lumping algorithms is a novel contribution. Using this approach, we have created a tool leveraging model based systems engineering technologies. The communicating Markov chains are specified using UML Statecharts via Papyrus extended using an ANTLR parsed domain specific language (DSL). The tool reduces the number of states in networks of Markov chains by several orders of magnitude. In one example, a network having a product state space of more than 600 million states is reduced to about 500 states. A feature of this technique is that the state space is examined incrementally, meaning that the full state space is never explicitly represented, even as an input to the reduction algorithm. The primary reduction appears to come from symmetry which is surprising because the technique includes no explicit symmetry handling. We note that composition is efficient at least for systems with high symmetry. We describe applications to a hospital intensive care unit (ICU) from a systems engineering perspective.},
	address = {Atlanta, GA},
	booktitle = {Conference on Systems Engineering Research (CSER{\textquoteright}13),},
	pages = {pp. 167-176}
}
@conference {
	title = {Interactive Tree Decomposition Tool for Reducing System Analysis Complexity},
	author = {Yang, Shahan., Wang, Baobing., Baras, John S.},
	year = {2013},
	month = {03/2013},
	abstract = {We present a graphical tool for the calculation of treewidth, a metric on the parametric structure of a system that is intimately tied to the complexity of system analysis. For many graphically describable systems, such as systems of parametric equations, as in a SysML Parametric diagram, or Bayesian networks or even mind maps and writing term papers, analysis of the system is exponential in treewidth and linear in system size. A tool facilitating comprehensive analysis can serve to bring competitive advantage to a systems engineering workflow by reducing costly unanticipated behaviors. Furthermore, a byproduct of computing treewidth is a framework for enumerating computationally compatible distributed algorithms. In this paper, we pose this NP-complete problem from the perspective of finding satisficing solutions, exposing choices that can influence the complexity of the resulting system to the designer. A designer can contribute two important things to the structure of the system: a visual intuition about the relationships between the underlying objects and the ability to change the relationships themselves at design time to reduce analysis complexity. Having a visual tool that provides instant feedback will help designers achieve an intuitive grasp of the relationship between design decisions and system complexity. As complexity is the root of almost every systems engineering problem, and also something not easily understood, incorporating complexity analysis into a design process should improve resulting system designs. The tool uses a randomized, anytime algorithm for interactive optimization of treewidth. It presents a sequence of choices to a designer and incrementally lowers an upper bound on system treewidth over time. This algorithm is novel, as few algorithms are targeted at interactivity with a human user. We present a number of simple examples for using the tool. We show how our tool helps to decompose some example systems, including a quadrotor optimization, a sensor network optimization, a Bayesian network, and a mind map.},
	address = {Atlanta, GA},
	booktitle = {Conference on Systems Engineering Research (CSER{\textquoteright}13),},
	pages = {pp. 138-147}
}
@conference {
	title = {Factor Join Trees in Systems Exploration},
	author = {Yang, Shahan., Baras, John S.},
	year = {2011},
	month = {11/2011},
	abstract = {The interaction of connected components creates complexity impeding the analysis of large systems. Thorough exploration, appearing as formal verification, optimization or constraint satisfaction typically has a complexity that is either a high order polynomial or an exponential function of system size. However, for a large class of systems the essential complexity is linear in system size and exponential in treewidth which makes the previous notion of exponential complexity in system size an accidental overestimate.

In this paper, we demonstrate how this reduced complexity can be achieved using summary propagation on factor graphs. We describe summary propagation in terms of operations belonging to a commutative semiring-weighted relational algebra. We show how by appropriate selection of the commutative semiring, the same solution applies to propositional satisfiability, inference on Bayesian networks and a mixed integer linear optimization problem motivated by the power restoration problem for distributed, autonomous networks. This solution leads to a non-iterative distributed algorithm that operates on local data.

While weighted relational algebraic operators are used as the basic means of calculation, the algorithm presented works only on factor graphs that are trees. This requires the calculation of a non-unique structure called a join tree, which can be trivially generated from a unique structure called a cliqueseparator graph, which can be computed in linear time from a SysML Parametric Diagram description of the system for chordal systems1 . Interesting artifacts arise from this structural analysis which may be interpreted as interfaces and components. The framework also contains mathematical artifacts that may be interpreted as hierarchy and abstraction. We develop a tool to assist in the structural analysis described and implementations of the described algorithms.},
	address = {Paris, France},
	booktitle = {23rd International Conference on Software and Systems Engineering and their Applications (ICSSEA 2011)},
	pages = {pp. 1-12}
}
@conference {
	title = {Modeling vulnerabilities of ad hoc routing protocols},
	author = {Yang, Shahan., Baras, John S.},
	year = {2003},
	month = {12/2003},
	abstract = {The purpose of this work is to automate the analysis of ad hoc routing protocols in the presence of attackers. To this end, a formal model fo protocol behavior is developed in which time is modeled by a set of constraints on the time of occurrence of events, enabling the representation of partially ordered timed events and asynchronous communication. Data variables are represented symbolically, capturing a range of distinct executions in each expression. Given a formal description of Ad Hoc On-Demand Distance Vector Routing Algorithm (AODV) and the desired safety property (route stability), an analysis by a naive semi-decision procedure discovers an instance of an attack that leads to a violation of the property.},
	address = {Fairfax, Virginia},
	booktitle = {1st ACM workshop on Security of ad hoc and sensor networks},
	pages = {pp. 12-20.},
	organization = {George Mason University}
}
@conference {
	title = {Correctness Proof for a Dynamic Adaptive Routing Algorithm for Mobile Ad-hoc Networks},
	author = {Yang, Shahan., Baras, John S.},
	year = {2003},
	month = {07/2003},
	abstract = {Dynamic and adaptive routing algorithms are the {\textquotedblleft}brains{\textquotedblright} of mobile ad-hoc networks (MANETs), in that they govern the self-organization of these networks. MANETs are infrastructureless {\textquotedblleft}intelligent{\textquotedblright} networks, which are becoming increasingly popular and have wide applicability. In this paper, we view dynamic adaptive routing algorithms for MANETs as hybrid systems (partly based on logic and partly based on numerics). In this paper, we introduce formal models for the analysis and verification of one such routing algorithm, the Temporally Oriented Routing Algorithm (TORA) under certain assumptions. More specifically we give a rigorous mathematical proof of correctness and convergence of TORA. Other formal methods, their limitations~and future research challenges are also discussed.},
	address = {Lake Baikal, Russia},
	booktitle = {IFAC Workshop \&ndash; Modeling and Analysis of Logic Controlled Dynamic Systems},
	pages = {pp. 1-10}
}
@conference {
	title = {Finite Automata Models for Anomaly Detection},
	author = {V. R. Ramezani, Yang, Shahan., Baras, John S.},
	year = {2003},
	month = {03/2003},
	abstract = {A fundamental problem in Intrusion detection is the fusion of dependent information sequences.In this paper ,we consider the fusion of two such sequences ,namely the sequence of system calls and the value of the instruction pointer.We introduce FAAD, a finite automation representation defined for the product alphabet of the two sequences where dependencies are implicitly taken into account by a matching procedure.},
	address = {Baltimore, Maryland},
	booktitle = {37th Conference on Information Sciences and Systems (CISS)},
	organization = {Johns Hopkins University}
}
@conference {
	title = {TORA, Verification, Proofs and Model Checking},
	author = {Yang, Shahan., Baras, John S.},
	year = {2003},
	month = {03/2003},
	address = {Sophia-Antipolis, France},
	booktitle = {WiOpt \&rsquo;03: Modeling and Optimization in Mobile, AdHoc and Wireless Networks}
}
@conference {
	title = {System designs for adaptive, distributed network monitoring and control},
	author = {Li, Hongjun., Yang, Shahan., Xi, Haifeng., Baras, John S.},
	year = {2001},
	month = {05/2001},
	abstract = {We present system designs for adaptive, distributed network monitoring and control. The ideas are to distribute some processing intelligence to network elements, and to design a dynamic interface such that the delegated agents could be managed remotely by the manager. The functionality of the delegated agents, and even that of the native software processes, could be extended dynamically without recompilation. The creation, deployment, operation, and management of the delegated agents require a standard infrastructure on each system where these agents need to be hosted. We use Java technology and C/C++ dynamic linkage mechanism to fulfill such a requirement under different situations and our system designs span a wide scope of applications},
	address = {Seattle, WA},
	booktitle = {IEEE/IFIP International Symposium on Integrated Network Management}
}
@techreport {
	title = {Compositional Analysis of Dynamic Bayesian Networks and Applications to CPS},
	author = {Yang, Shahan., Zhou, Yuchen., Baras, John S.},
	year = {2012},
	month = {12/2012},
	abstract = {Dynamic Bayesian networks (DBNs) can be effectively used to model various problems in complex dynamic systems. We perform an empirical investigation on compositional analysis of DBNs using abstraction. In static systems and hidden Markov models, computation of a metric called treewidth induces a tree decomposition that can be used to perform logical or probabilistic inference and max + optimizations in time exponential in treewidth and linear in overall system size. Intuitively, the linear scaling means that very large systems can be analyzed as long as they are sufficiently sparse and well structured. In these simple cases, summary propagation, which uses two operations, summation (projection) and product (composition), suffices to perform the inference or optimization. Here, we begin an extension of this to structured networks of communicating dynamic systems. We define generalizations of projection and composition operators that treat labeled Markov chains as primitive objects. The projection operation, corresponding to summation, is implemented as label deletion followed by exact state reduction for Markov chains, similar to Hopcroft{\textquoteright}s DFA minimization algorithm, with O(n log m) complexity. The composition operation is the product of state machines. We use canonical MDDs, similar to BDDs, to capture logical dependencies symbolically. Combining symbolic representations with Markov chain lumping algorithms is a novel contribution. Using this approach, we have created a tool leveraging model based systems engineering technologies. The communicating Markov chains are specified using UML Statecharts via Papyrus extended using an ANTLR parsed domain specific language (DSL). The tool reduces the number of states in networks of Markov chains by several orders of magnitude. In one example, a network having a product state space of more than 600 million states is reduced to about 500 states. A feature of this technique is that the state space is examined incrementally, meaning that the full state space is never explicitly represented, even as an input to the reduction algorithm. The primary reduction appears to come from symmetry which is surprising because the technique includes no explicit symmetry handling. We note that composition is efficient at least for systems with high symmetry. We describe applications to a hospital intensive care unit (ICU) from a systems engineering perspective.}
}
@techreport {
	title = {On System Designs of Distributed, Extensible Framework for Network Monitoring and Control},
	author = {Li, Hongjun., Yang, Shahan.},
	year = {2001},
	month = {01/2001},
	abstract = {In this paper, we present a distributed, extensible framework for supporting adaptive, dynamic network monitoring and control. We borrow the paradigm of management by delegation [8] and distribute some processing intelligence to network elements. The functionality of the delegated agents, and even that of the native software processes, could be extended dynamically without recompilation. Such procedure is called change of logic and we explain it in the framework of communicating finite state machines for extending native process functionality. We use Java technology and C/C++ dynamic linkage mechanism to achieve the standard hosting infrastructure for these agents and our system designs span a wide scope of applications.},
	number = {Number: CSHCN TR 2001-12}
}
