Sabina Petride

Binary XML storage and query processing in Oracle 11g

Oracle RDBMS has supported XML data management for more than six years since version 9i. Prior to 11g, text-centric XML documents can be stored as-is in a CLOB column and schema-based data-centric documents can be shredded and stored in object-relational (OR) tables mapped from their XML Schema. However, both storage formats have intrinsic limitations---XML/CLOB has unacceptable query and update performance, and XML/OR requires XML schema. To tackle this problem, Oracle 11g introduces a native Binary XML storage format and a complete stack of data management operations. Binary XML was designed to address a wide range of real application problems encountered in XML data management---schema flexibility, amenability to XML indexes, update performance, schema evolution, just to name a few. n nIn this paper, we introduce the Binary XML storage format based on Oracle SecureFiles System[21]. We propose a lightweight navigational index on top of the storage and an NFA-based navigational algorithm to provide efficient streaming processing. We further optimize query processing by exploiting XML structural and schema information that are collected in database dictionary. We conducted extensive experiments to demonstrate high performance of the native Binary XML in query processing, update, and space consumption.

Perfect cryptography, S5 knowledge, and algorithmic knowledge

We propose a principled approach to model secrecy in multiagent systems, by defining a set of possible observations and providing agents with algorithms used to distinguish the possible states of the system. Our approach fits naturally within a knowledge-based account of secrecy. By adjusting both the kind of observations and the capabilities of the agents, we can capture in a natural way different forms of secrecy in the presence of perfect cryptography. In particular, we show how to model extraction secrecy. Our formalization suggests a unified definition of secrecy for cryptographic protocols and for systems that seek to prevent inadmissible flows of information.

Knowledge-Based Synthesis of Distributed Systems Using Event Structures

To produce a program guaranteed to satisfy a given specification one cannsynthesize it from a formal constructive proof that a computation satisfyingnthat specification exists. This process is particularly effective if thenspecifications are written in a high-level language that makes it easy forndesigners to specify their goals. We consider a high-level specificationnlanguage that results from adding knowledge to a fragment of Nuprl specificallyntailored for specifying distributed protocols, called event theory. We thennshow how high-level knowledge-based programs can be synthesized from thenknowledge-based specifications using a proof development system such as Nuprl.nMethods of Halpern and Zuck then apply to convert these knowledge-basednprotocols to ordinary protocols. These methods can be expressed as heuristicntransformation tactics in Nuprl.