Papers by Alexandra Meliou
Abstract How-To queries answer fundamental data analysis questions of the form:" How should the i... more Abstract How-To queries answer fundamental data analysis questions of the form:" How should the input change in order to achieve the desired output". As a Reverse Data Management problem, the evaluation of how-to queries is harder than their" forward" counterpart: hypothetical, or what-if queries.
Abstract A surprising query result is often an indication of errors in the query or the underlyin... more Abstract A surprising query result is often an indication of errors in the query or the underlying data. Recent work suggests using causal reasoning to find explanations for the surprising result. In practice, however, one often has multiple queries and/or multiple answers, some of which may be considered correct and others unexpected. In this paper, we focus on determining the causes of a set of unexpected results, possibly conditioned on some prior knowledge of the correctness of another set of results.
Page 1. CS271 Randomness & Computation Fall 2011 Lecture 14: October 11 Lecturer: Alistair Sincla... more Page 1. CS271 Randomness & Computation Fall 2011 Lecture 14: October 11 Lecturer: Alistair Sinclair Based on scribe notes by: A. Meliou, M. Narayanan; Y. Singer, M. Schuster Disclaimer: These notes have not been subjected to the usual scrutiny reserved for formal publications. They may be distributed outside this class only with the permission of the Instructor. 14.1 Finding Hamilton Cycles in Random Graphs A Hamiltonian cycle in a graph is a cycle that contains every vertex exactly once.
Abstract We show that the default-all propagation scheme for database annotations is dangerous. D... more Abstract We show that the default-all propagation scheme for database annotations is dangerous. Dangerous here means that it can propagate annotations to the query output which are semantically irrelevant to the query the user asked. This is the result of considering all relationally equivalent queries and returning the union of their where-provenance in an attempt to define a propagation scheme that is insensitive to query rewriting.
Abstract In many sensing applications we must continuously gather information to provide a good e... more Abstract In many sensing applications we must continuously gather information to provide a good estimate of the state of the environment at every point in time. A robot may tour an environment, gathering information every hour. In a wireless sensor network, these tours correspond to packets being transmitted. In these settings, we are often faced with resource restrictions, like energy constraints. The users issue queries with certain expectations on the answer quality.
Abstract Provenance is often used to validate data, by verifying its origin and explaining its de... more Abstract Provenance is often used to validate data, by verifying its origin and explaining its derivation. When searching for “causes” of tuples in the query results or in general observations, the analysis of lineage becomes an essential tool for providing such justifications. However, lineage can quickly grow very large, limiting its immediate use for providing intuitive explanations to the user.
The Semantic Web is the next step of the current Web where information will become more machine-u... more The Semantic Web is the next step of the current Web where information will become more machine-understandable to support effective data discovery and integration. Hierarchical schemas, either in the form of tree-like structures (eg, DTDs, XML schemas), or in the form of hierarchies on a category/subcategory basis (eg, thematic hierarchies of portal catalogs), play an important role in this task. They are used to enrich semantically the available information.
ABSTRACT In this paper, we propose causality as a unified framework to explain query answers and ... more ABSTRACT In this paper, we propose causality as a unified framework to explain query answers and non-answers, thus generalizing and extending several previously proposed approaches of provenance and missing query result explanations. We develop our framework starting from the well-studied definition of actual causes by Halpern and Pearl [13].
ABSTRACT Database research mainly focuses on forward-moving data flows: source data is subjected ... more ABSTRACT Database research mainly focuses on forward-moving data flows: source data is subjected to transformations and evolves through queries, aggregations, and view definitions to form a new target instance, possibly with a different schema. This Forward Paradigm underpins most data management tasks today, such as querying, data integration, data mining, etc.
Abstract In this demo, we will present Tiresias, the first how-to query engine. How-to queries re... more Abstract In this demo, we will present Tiresias, the first how-to query engine. How-to queries represent fundamental data analysis questions of the form:" How should the input change in order to achieve the desired output". They exemplify an important Reverse Data Management problem: solving constrained optimization problems over data residing in a DBMS.
Sensing devices are now used by many practical applications that require monitoring of physical p... more Sensing devices are now used by many practical applications that require monitoring of physical phenomena. Measurements like temperature, humidity, light, and acceleration are gathered at various locations and then distributed and stored in the network of sensors, or transmitted over the wireless medium towards a central location. This data is later used to extract information on the specific phenomenon observed.
Abstract The simulation of structural and geotechnical systems is a critical step in their design... more Abstract The simulation of structural and geotechnical systems is a critical step in their design and assessment. The purpose of an earthquake simulation is to estimate the performance of the system under seismic excitation or loads that represent the effects of an earthquake. Structural and geotechnical simulation has a long history of development in earthquake engineering. The computation required to perform large scale simulations, however, is not suitable to be handled sequentially.
Abstract A basic task in sensor networks is to interactively gather data from a subset of the sen... more Abstract A basic task in sensor networks is to interactively gather data from a subset of the sensor nodes. When data needs to be gathered from a selected set of nodes in the network, existing communication schemes often behave poorly. In this paper, we study the algorithmic challenges in efficiently routing a fixed-size packet through a small number of nodes in a sensor network, picking up data as the query is routed.
ABSTRACT In this work we present new in-network techniques for communication-efficient approximat... more ABSTRACT In this work we present new in-network techniques for communication-efficient approximate query processing in wireless sensornets. We use a model-based approach that constructs and maintains a spanning tree within the network, rooted at the basestation. The tree maintains compressed summary information for each link that is used to “stub out” traversal during query processing. Our work is based on a formal model of the in-network tree construction task framed as an optimization problem.
Abstract An answer to a query has a well-defined lineage expression (alternatively called how-pro... more Abstract An answer to a query has a well-defined lineage expression (alternatively called how-provenance) that explains how the answer was derived. Recent work has also shown how to compute the lineage of a non-answer to a query. However, the cause of an answer or non-answer is a more subtle notion and consists, in general, of only a fragment of the lineage.
Abstract: In this work we present in-network techniques to improve the efficiency of spatial aggr... more Abstract: In this work we present in-network techniques to improve the efficiency of spatial aggregate queries. Such queries are very common in a sensornet setting, demanding more targeted techniques for their handling. Our approach constructs and maintains multi-resolution cube hierarchies inside the network, which can be constructed in a distributed fashion. In case of failures, recovery can also be performed with in-network decisions.
ABSTRACT In this paper, we propose causality as a unified framework to explain query answers and ... more ABSTRACT In this paper, we propose causality as a unified framework to explain query answers and non-answers, thus generalizing and extending several previously proposed approaches of provenance and missing query result explanations. We develop our framework starting from the well-studied definition of actual causes by Halpern and Pearl [13]. After identifying some undesirable characteristics of the original definition, we propose functional causes as a refined definition of causality with several desirable properties.
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Papers by Alexandra Meliou