Ganesh Ram Santhanam

Web Service Substitution Based on Preferences Over Non-functional Attributes

In many applications involving composite Web services, one or more component services may become unavailable. This presents us with the problem of identifying other components that can take their place, while maintaining the overall functionality of the composite service. Given a choice of candidate substitutions that offer the desired functionality, it is often necessary to select the most preferred substitution based on non-functional attributes of the service, e.g., security, reliability, etc. We propose an approach to this problem using preference networks for representing and reasoning about preferences over non-functional properties. We present algorithms for solving several variants of this problem: a) when the choice of the preferred substitution is independent of the other constituents of the composite service; b) when the choice of the preferred substitution depends on the other constituents of the composite service; and c) when multiple constituents of a composite service need to be replaced simultaneously. The proposed solutions to the service substitution problem based on preferences over non-functional properties are independent of the specific formalism used to represent functional requirements of a composite service as well as the specific algorithm used to assemble the composite service.

TCP - Compose * --- A TCP-Net Based Algorithm for Efficient Composition of Web Services Using Qualitative Preferences

In many practical applications, trade-offs involvingnon-functional attributes e.g., availability, performance play animportant role in selecting component services in assembling afeasible composition, i.e., a composite service that achieves thedesired functionality. We present TCP - Compose *, analgorithm for service composition that identifies, from a set ofcandidate solutions that achieve the desired functionality, a setof composite services that are non-dominated by any othercandidate with respect to the user-specified qualitativepreferences over non-functional attributes. We use TCP-net, agraphical modeling paradigm for representing and reasoning withqualitative preferences and importance. We propose a heuristic forestimating the preference ordering over the different choices ateach stage in the composition to improve the efficiency of TCP -Compose *. We establish the conditions under which TCP -Compose * is guaranteed to generate a set of compositeservices that (a) achieve the desired functionality and (b)constitute a non-dominated set of solutions with respectto the user-specified preferences and tradeoffs over thenon-functional attributes.

Identifying Optimal Composite Services by Decomposing the Service Composition Problem

For a Web service composition to satisfy a users needs, it must not only provide the desired functionality, but also have nonfunctional properties (e.g., reliability, availability, cost) that are acceptable to the user. In the recent past, several techniques have been developed and deployed to identify a composite service that conforms to the functional requirements and is also optimal with respect to the user-defined preferences over non-functional properties. However, these composition techniques are limited to using one formalism for specifying the required functionality, in short, the existing techniques cannot identify optimal (w.r.t. non-functional properties) composite services that are required to satisfy functional requirements described in multiple formalisms. We have previously proposed a meta-framework for service composition that involves decomposing the required functionality into a boolean combination of atomic requirements, which are expressed using different formalisms. This meta-framework supports the use of multiple formalisms and their corresponding composition algorithms within a single scenario. In this paper, we integrate support for unconditional preferences over nonfunctional requirements into this composition meta-framework. We show that for a large class of problems, local selection of preferred service(s) can yield the most preferred composite service that satisfies the desired functional requirements.

Representing and reasoning with qualitative preferences for compositional systems

Many applications, e.g., Web service composition, complex system design, team formation, etc., rely on methods for identifying collections of objects or entities satisfying some functional requirement. Among the collections that satisfy the functional requirement, it is often necessary to identify one or more collections that are optimal with respect to user preferences over a set of attributes that describe the non-functional properties of the collection. We develop a formalism that lets users express the relative importance among attributes and qualitative preferences over the valuations of each attribute. We define a dominance relation that allows us to compare collections of objects in terms of preferences over attributes of the objects that make up the collection. We establish some key properties of the dominance relation. In particular, we show that the dominance relation is a strict partial order when the intra-attribute preference relations are strict partial orders and the relative importance preference relation is an interval order. We provide algorithms that use this dominance relation to identify the set of most preferred collections. We show that under certain conditions, the algorithms are guaranteed to return only (sound), all (complete), or at least one (weakly complete) of the most preferred collections. We present results of simulation experiments comparing the proposed algorithms with respect to (a) the quality of solutions (number of most preferred solutions) produced by the algorithms, and (b) their performance and efficiency. We also explore some interesting conjectures suggested by the results of our experiments that relate the properties of the user preferences, the dominance relation, and the algorithms.

Model Checking of Qualitative Sensitivity Preferences to Minimize Credential Disclosure

In most client-server interactions over the Web, the server requires the client to disclose certain credentials before providing the client with the requested service (server policy). The client, on the other hand, wants to minimize the sensitivity of the set of credentials disclosed (client preference). We present a qualitative preference formalism based on conditional importance networks (CI-nets) for representing and reasoning with client preferences over the relative sensitivity of sets of credentials. The semantics of CI-net preferences is described using a preference graph over the set of credentials for which the preferences are expressed. We develop a model checking-based approach for analyzing the preference graph, efficiently verifying whether one set of credentials is more sensitive than another (dominance testing). Further, we identify the least (minimum) sensitive set of information that may be disclosed by the client to get access to the desired service. We present a technique based on iterative verification and refinement of the preference graph for computing a sequence of credential sets, ensuring that a credential set with higher sensitivity is never returned before one with lower sensitivity. We present a prototype implementation and preliminary simulation results.

On Utilizing Qualitative Preferences in Web Service Composition: A CP-net Based Approach

Traditional approaches to Web service composition have focused on either generating compositions that match the structural and functional requirements of the user, or using quantitative optimization techniques over non-functional attributes. However, users preferences and trade-offs are often qualitative over non-functional attributes of the goal service like security, performance, cost. We propose to capture such requirements as qualitative preferences in addition to structural and functional constraints of the composite goal service. We analyze the theory of CP-nets as a formal model for representing and reasoning with qualitative preferences, and show how it can be used to improve the quality of the generated composition and scalability of the composition algorithm.

Automating analysis of qualitative preferences in goal-oriented requirements engineering

In goal-oriented requirements engineering, a goal model graphically represents relationships between the required goals (functional requirements), tasks (realizations of goals), and optional goals (non-functional properties) involved in designing a system. It may, however, be impossible to find a design that fulfills all required goals and all optional goals. In such cases, it is useful to find designs that provide the required functionality while satisfying the most preferred set of optional goals under the goal models constraints. We present an approach that considers expressive qualitative preferences over optional goals, as these can model interacting and/or mutually exclusive subgoals. Our framework employs a model checking-based method for reasoning with qualitative preferences to identify the most preferred alternative(s). We evaluate our approach using existing goal models from the literature.

Identifying a preferred countermeasure strategy for attack graphs

Attack graphs capture sequences of actions that an intruder can take to lead the system to an undesirable state. They have proven to be important tools for administrators to analyse and devise countermeasures to be deployed in the face of an attack. We consider preferences over countermeasures that the administrator may hold when devising a strategy to thwart the attackers goals. We present a formalism based on CI-nets to represent and reason about such preferences. We present a method to find an intervention strategy in terms of a set of countermeasures that is guaranteed to thwart any attack on the system, which is also most preferred.

Pavement Life-Cycle Sustainability Assessment and Interpretation Using a Novel Qualitative Decision Procedure

AbstractA novel approach to life-cycle sustainability (impact) assessment and interpretation procedure on the basis of multiple criteria is developed in this paper for the comparison and evaluation of alternative road pavement designs. A case study reported in the literature, which compared pavement structures with virgin materials as well as industrial by-products such as coal ash, crushed concrete waste, and granulated blast-furnace slag, was examined in the context of multicriteria decision analysis (MCDA) using the proposed approach. The environmental loadings assessed during the life cycle of the pavement structures included natural raw materials and secondary products, energy and fuel consumption, emissions of carbon dioxide (CO2), nitrogen oxides (NOx), sulphur dioxide (SO2), volatile organic compounds (VOCs), carbon monoxide (CO) and particles, dust emissions, compounds leaching into the soil, and noise. The proposed qualitative decision approach to life cycle-based environmental impact assessment...

Preference Based Service Adaptation Using Service Substitution

In many applications such as service-oriented computing, users often prefer some compositions over the others based on their preferences over non-functional attributes such as security and cost. After a composition is deployed, apart from changes in the functional requirements, service-oriented architectures often have to deal with changes in the user preferences over the non-functional attributes and/or repository of available components. We formulate the problem of adaptation as iterative substitution of appropriate components in a composition, and provide two algorithms that produce a sequence of increasingly preferred adaptations with time: a fast algorithm that searches for preferred adaptations by improving the valuation of the relatively more important attributes, and another that is computationally more intensive but guaranteed to produce at least one preferred adaptation, if one exists.