The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform

Vijayalakshmi Atluri - One of the best experts on this subject based on the ideXlab platform.

  • the role hierarchy mining Problem Discovery of optimal role hierarchies
    Annual Computer Security Applications Conference, 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

  • ACSAC - The Role Hierarchy Mining Problem: Discovery of Optimal Role Hierarchies
    2008 Annual Computer Security Applications Conference (ACSAC), 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

James R. Lewis - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Level of Problem Description on Problem Discovery Rates: Two Case Studies
    Proceedings of the Human Factors and Ergonomics Society Annual Meeting, 2006
    Co-Authors: James R. Lewis
    Abstract:

    The primary purpose of this analysis was to investigate the effect of changing the level of description of usability Problems on the estimate of the Problem Discovery rate (p). A secondary purpose was to describe a method for using p to estimate the number of Problems remaining available for Discovery given the constraints associated with a particular participant population, application, and set of tasks. The level of Problem description influenced estimates of p, and the direction of influence was predictable, with higher levels of description producing higher estimates of p. Practitioners need a level of description that flows easily into recommendations for redesigning products, but to keep usability studies as efficient as possible, practitioners also need to seek a level of description that takes advantage of common patterns in observed usability Problems. Managing this tradeoff is only one of the challenges of usability evaluation, but it is an important one.

  • Determining Usability Test Sample Size
    2006
    Co-Authors: Carl W. Turner, James R. Lewis, Jakob Nielsen
    Abstract:

    Virzi (1992), Nielsen and Landauer (1993), and Lewis (1994) have published influential articles on the topic of sample size in usability testing. In these articles, the authors presented a mathematical model of Problem Discovery rates in usability testing. Using the Problem Discovery rate model, they showed that it was possible to determine the sample size needed to uncover a given proportion of Problems in an interface during one test. The authors presented empirical evidence for the models and made several important claims:

  • Evaluation of Procedures for Adjusting Problem-Discovery Rates Estimated From Small Samples
    International Journal of Human-computer Interaction, 2001
    Co-Authors: James R. Lewis
    Abstract:

    There are 2 excellent reasons to compute usability Problem-Discovery rates. First, an estimate of the Problem-Discovery rate is a key component for projecting the required sample size for a usability study. Second, practitioners can use this estimate to calculate the proportion of discovered Problems for a given sample size. Unfortunately, small-sample estimates of the Problem-Discovery rate suffer from a serious overestimation bias. This bias can lead to serious underestimation of required sample sizes and serious overestimation of the proportion of discovered Problems. This article contains descriptions and evaluations of a number of methods for adjusting small-sample estimates of the Problem-Discovery rate to compensate for this bias. A series of Monte Carlo simulations provided evidence that the average of a normalization procedure and Good-Turing (Jelinek, 1997; Manning & Schutze, 1999) discounting produces highly accurate estimates of usability Problem-Discovery rates from small sample sizes.

  • Introduction: Current Issues in Usability Evaluation
    International Journal of Human-computer Interaction, 2001
    Co-Authors: James R. Lewis
    Abstract:

    In this introduction to the special issue of the International Journal of Human-Computer Interaction, I discuss some current topics in usability evaluation and indicate how the contributions to the issue relate to these topics. The contributions cover a wide range of topics in usability evaluation, including a discussion of usability science, how to evaluate usability evaluation methods, the effect and control of certain biases in the selection of evaluative tasks, a lack of reliability in Problem detection across evaluators, how to adjust estimates of Problem-Discovery rates computed from small samples, and the effects of perception of hedonic and ergonomic quality on user ratings of a product's appeal.

  • Sample Sizes for Usability Studies: Additional Considerations
    Human Factors, 1994
    Co-Authors: James R. Lewis
    Abstract:

    Recently, Virzi (1992) presented data that support three claims regarding sample sizes for usability studies: (1) observing four or five participants will allow a usability practitioner to discover 80% of a product's usability Problems, (2) observing additional participants will reveal fewer and fewer new usability Problems, and (3) more severe usability Problems are easier to detect with the first few participants. Results from an independent usability study clearly support the second claim, partially support the first, but fail to support the third. Problem Discovery shows diminishing returns as a function of sample size. Observing four to five participants will uncover about 80% of a product's usability Problems as long as the average likelihood of Problem detection ranges between 0.32 and 0.42, as in Virzi. If the average likelihood of Problem detection is lower, then a practitioner will need to observe more than five participants to discover 80% of the Problems. Using behavioral categories for proble...

Qi Guo - One of the best experts on this subject based on the ideXlab platform.

  • the role hierarchy mining Problem Discovery of optimal role hierarchies
    Annual Computer Security Applications Conference, 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

  • ACSAC - The Role Hierarchy Mining Problem: Discovery of Optimal Role Hierarchies
    2008 Annual Computer Security Applications Conference (ACSAC), 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

Jaideep Vaidya - One of the best experts on this subject based on the ideXlab platform.

  • the role hierarchy mining Problem Discovery of optimal role hierarchies
    Annual Computer Security Applications Conference, 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

  • ACSAC - The Role Hierarchy Mining Problem: Discovery of Optimal Role Hierarchies
    2008 Annual Computer Security Applications Conference (ACSAC), 2008
    Co-Authors: Qi Guo, Jaideep Vaidya, Vijayalakshmi Atluri
    Abstract:

    Role hierarchies are fundamental to the role based access control (RBAC) model. The notion of role hierarchy is a well understood concept that allows senior roles to inherit the permissions of the corresponding junior roles. Role hierarchies further ease the burden of security administration, as there is no need to explicitly specify and maintain a large number of permissions. Given a set of roles or user permissions, one may construct a number of alternative hierarchies. However, there does not exist the notion of an optimal role hierarchy. Optimality helps in maximizing the benefit of employing the role hierarchy. In this paper, we propose such a formal metric. Our optimality notion is based on the smallest graph representation of the role hierarchy (minimal in the number of edges) having the same transitive closure as any alternate representation. We show why this makes sense as well as ways to achieve this. The main contributions of this paper are to formalize the notion of optimality for role hierarchy construction, along with proposing heuristic solutions to achieve this objective, thus making role hierarchies feasible and practical.

Nenad Stojanovic - One of the best experts on this subject based on the ideXlab platform.

  • WISE - On the role of query refinement in searching for information: the librarian agent query refinement process
    Proceedings of the 7th International Conference on Properties and Applications of Dielectric Materials (Cat. No.03CH37417), 2003
    Co-Authors: Nenad Stojanovic
    Abstract:

    In this paper we present an approach for the query refinement called librarian agent query refinement process, which simulates the role a human librarian plays in the searching for information resources in a library. The process consists of two phases: Problem Discovery, in which the potential Problems (ambiguities) of the initial query are discovered and estimated and query refinement, which analyses these ambiguities in order to provide suitable modification of that query that increases the precision and recall of the searching process. The agent performs comprehensive analyses of a query, based on the structure of the used vocabulary in an information portal and the content of its information repository. Moreover, the information about the previous users' behaviour and the activities of the current user are used for making the query refinement process more efficient (i.e. usage-driven and personalized). From the user's point of view, the main advantage of such an approach is that it enables a user to satisfy his information need in a more intuitive and efficient way.