Repairing Inconsistent XML Write-Access Control Policies

XML access control policies involving updates may contain security flaws, here called inconsistencies, in which a forbidden operation may be simulated by performing a sequence of allowed operations. This paper investigates the problem of deciding whether a policy is consistent, and if not, how its inconsistencies can be repaired. We consider policies expressed in terms of annotated DTDs defining which operations are allowed or denied for the XML trees that are instances of the DTD. We show that consistency is decidable in PTIME for such policies and that consistent partial policies can be extended to unique "least-privilege" consistent total policies. We also consider repair problems based on deleting privileges to restore consistency, show that finding minimal repairs is NP-complete, and give heuristics for finding repairs.Comment: 25 pages. To appear in Proceedings of DBPL 200

Consistency in Continuous Distributed Interactive Media

In this paper we investigate how consistency can be ensured for continuous distributed interactive media, i.e. distributed media which change their state in reaction to user initiated operations as well as because of the passing of time. Existing approaches to reach consistency in discrete distributed interactive media are briefly outlined and it is shown that these fail in the continuous domain. In order to allow a thorough discussion of the problem, a formal definition of the term consistency in the continuous domain is given. Based on this definition we show that an important trade off relationship exists between the responsiveness of the medium and the appearance of short term inconsistencies. Currently this trade off is not taken into consideration for consistency in the continuous domain, thereby severely limiting the consistency related fidelity for a large number of applications. We show that for those applications the fidelity can be significantly raised by voluntarily decreasing the responsiveness of the medium. This concept is called local lag and it enables the distribution of continuous interactive media which are more vulnerable to short term inconsistencies than e.g. battlefield simulations. We prove that the concept of local lag is valid by describing how local lag was successfully used to ensure consistency in a 3D telecooperation application

Priority-Based Conflict Resolution in Inconsistent Relational Databases

We study here the impact of priorities on conflict resolution in inconsistent relational databases. We extend the framework of repairs and consistent query answers. We propose a set of postulates that an extended framework should satisfy and consider two instantiations of the framework: (locally preferred) l-repairs and (globally preferred) g-repairs. We study the relationships between them and the impact each notion of repair has on the computational complexity of repair checking and consistent query answers

Data Cleaning for XML Electronic Dictionaries via Statistical Anomaly Detection

Many important forms of data are stored digitally in XML format. Errors can occur in the textual content of the data in the fields of the XML. Fixing these errors manually is time-consuming and expensive, especially for large amounts of data. There is increasing interest in the research, development, and use of automated techniques for assisting with data cleaning. Electronic dictionaries are an important form of data frequently stored in XML format that frequently have errors introduced through a mixture of manual typographical entry errors and optical character recognition errors. In this paper we describe methods for flagging statistical anomalies as likely errors in electronic dictionaries stored in XML format. We describe six systems based on different sources of information. The systems detect errors using various signals in the data including uncommon characters, text length, character-based language models, word-based language models, tied-field length ratios, and tied-field transliteration models. Four of the systems detect errors based on expectations automatically inferred from content within elements of a single field type. We call these single-field systems. Two of the systems detect errors based on correspondence expectations automatically inferred from content within elements of multiple related field types. We call these tied-field systems. For each system, we provide an intuitive analysis of the type of error that it is successful at detecting. Finally, we describe two larger-scale evaluations using crowdsourcing with Amazon's Mechanical Turk platform and using the annotations of a domain expert. The evaluations consistently show that the systems are useful for improving the efficiency with which errors in XML electronic dictionaries can be detected.Comment: 8 pages, 4 figures, 5 tables; published in Proceedings of the 2016 IEEE Tenth International Conference on Semantic Computing (ICSC), Laguna Hills, CA, USA, pages 79-86, February 201

Repairs of databases with null values

Dissertação para obtenção do Grau de Mestre em Engenharia InformáticaDatabases store information that is intended to model the real world and to help in modeling, they use constraints that shape the information according to the world view. However, when a new constraint is defined, the data contained in the database may not respect it and so the database should be repaired. Those repairs are made by adding, removing or updating tuples, making as few modifications as possible to satisfy the constraints. In order to determine the repairs of a database with respect to new constraints, there are already some available approaches that provide a solution. But databases also need to contain information that is absence, which is represented through null values. Null values are not regular values and they represent information that is missing or unknown. When using null values, there is no consensus in the literature on how to interpret them when checking constraint satisfaction. Also, there is not a practical implementation to do the repairing regarding null values. In this document, we study the problem of dealing with null values in the repairing process and propose a (both practical and theoretically sound) solution for this problem including the definition of semantics for null values to achieve constraint satisfaction, and how to proceed to make the databases repairs, ending with a practical implementation of the proposed solution using Answer-set Programming.FCT project ASPEN - Answer Set Programming with BoolEaN Satisfiability (PTDC/EIA-CCO/110921/2009