4639514
Group Hierarchies with Constrained User Assignment in Linux
In this paper we investigate one aspect of RBAC administration concerning assignment of users to roles. A user-role assignment model can also be used for managing user-group assignment. We overview a constrained user-group assignment model and describe its implementation in the Linux system. Rather than set user and file rights individually for each and every user, the administrator can give rights to various groups, then place users within those groups in Linux. Each user within a group inherits the rights associated with that group. We describe an experiment to extend the Linux group mechanism to include group hierarchies and decentralized user-group assignment can be implemented by means of setgid programs.
7349909
Reconstructing a formal security model
Abstract Role-based access control (RBAC) is a flexible approach to access control, which has generated great interest in the security community. The principal motivation behind RBAC is to simplify the complexity of administrative tasks. Several formal models of RBAC have been introduced. However, there are a few works specifying RBAC in a way which system developers or software engineers can easily understand and adopt to develop role-based systems. And there still exists a demand to have a practical representation of well-known access control models for system developers who work on secure system development. In this paper we represent a well-known RBAC model with software engineering tools such as Unified Modeling Language (UML) and Object Constraints Language (OCL) to reduce a gap between security models and system developments. The UML is a general-purpose visual modeling language in which we can specify, visualize, and document the components of a software system. And OCL is part of the UML and has been used for object-oriented analysis and design as a de facto constraints specification language in software engineering arena. Our representation is based on a standard model for RBAC proposed by the National Institute of Standards and Technology. We specify this RBAC model with UML including three views: static view, functional view, and dynamic view. We also describe how OCL can specify RBAC constraints that is one of important aspects to constrain what components in RBAC are allowed to do. In addition, we briefly discuss future directions of this work.
11764310
Symmetric drawings of triconnected planar graphs
Symmetry is one of the most important aesthetic criteria in graph drawing because it reveals structure in the graph. To draw graphs symmetrically, we need two steps. The first step is to find appropriate automorphisms. The second step is to draw the graph to display the automorphisms. Our aim in this paper is to construct maximally symmetric straight-line drawings of triconnected planar graphs in linear time. Previously known algorithms run in quadratic time. We show that an algorithm of Fontet can be used to find an embedding in the plane with the maximum number of symmetries, and present a new algorithm for finding a straight line drawing that achieves that maximum. Both algorithms run in linear time.
1395152
A Group-Theoretic Method for Drawing Graphs Symmetrically
Constructing symmetric drawings of graphs is NP-hard. In this paper, we present a new method for drawing graphs symmetrically based on group theory. More formally, we define a n-geometric automorphism group of a graph that can be displayed as symmetries of a drawing of the graph in n dimensions. Then we present an algorithm to find all 2- and 3-geometric automorphism groups of a graph. We implement the algorithm using Magma [11] and the experimental results shows that our approach is very efficient in practice. We also present a drawing algorithm to display a 2- or 3-geometric automorphism group.
40285902
Isoperimetric numbers and bisection widths of double coverings of a complete graph
1910054
A neuromorphic model for achromatic and chromatic surface representation of natural images
This study develops a neuromorphic model of human lightness perception that is inspired by how the mammalian visual system is designed for this function. It is known that biological visual representations can adapt to a billion-fold change in luminance. How such a system determines absolute lightness under varying illumination conditions to generate a consistent interpretation of surface lightness remains an unsolved problem. Such a process, called 'anchoring' of lightness, has properties including articulation, insulation, configuration, and area effects. The model quantitatively simulates such psychophysical lightness data, as well as other data such as discounting the illuminant, and lightness constancy and contrast effects. The model retina embodies gain control at retinal photoreceptors, and spatial contrast adaptation at the negative feedback circuit between mechanisms that model the inner segment of photoreceptors and interacting horizontal cells. The model can thereby adjust its sensitivity to input intensities ranging from dim moonlight to dazzling sunlight. A new anchoring mechanism, called the Blurred-Highest-Luminance-As-White rule, helps simulate how surface lightness becomes sensitive to the spatial scale of objects in a scene. The model is also able to process natural color images under variable lighting conditions, and is compared with the popular RETINEX model.
20165974
An intelligent image retrieval system using XML
With the rapid development of Internet technology, the number of Internet users and the amount of multimedia information on the Internet is ever increasing. Recently, the Web sites, such as e-business sites and shopping mall sites, deal with lots of image information. As a result, it is required to support content-based image retrieval efficiently on such image data. This paper proposes an intelligent image retrieval system, which adopts XML technology. To support object-based content retrieval on product catalog images containing multiple objects, we describe a multilevel metadata structure representing the local features, global features, and semantics of image data. To enable semantic-based and content-based retrieval on such image data, we design an XML-schema for the proposed metadata. We also describe how to automatically transform the retrieval results into the forms suitable for the various user environments, such as Web browser or mobile browser, using XSLT. The proposed scheme can be utilized to enable efficient image metadata sharing between systems, and it will contribute in improving the retrieval correctness and the user's satisfaction on content-based e-catalog image retrieval.