arXiv subjects

Matthew Damigos

Publications and source records attributed to Matthew Damigos.

5 recordsLinked to original sources

arXiv2025

Semi-interval Comparison Constraints in Query Containment and Their Impact on Certain Answer Computation

We consider conjunctive queries with arithmetic comparisons (CQAC) and investigate the computational complexity of the problem: Given two CQAC queries, $Q$ and $Q'$, is $Q'$ contained in $Q$? We know that, for CQAC queries, the problem of testing containment is $\Pi_2 ^p$ -complete. However, there are broad classes of queries with semi-interval arithmetic comparisons in the containing query that render the problem solvable in NP. In all cases examined the contained query is allowed to be any CQAC. Interestingly, we also prove that there are simple cases where the problem remains $\Pi_2 ^p$ -complete. We also investigate the complexity of computing certain answers in the framework of answering CQAC queries with semi-interval comparisons using any CQAC views. We prove that maximally contained rewritings in the language of union of CQACs always compute exactly all certain answers. We find cases where we can compute certain answers in polynomial time using maximally contained rewritings.

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arXiv2022

Evaluating Continuous Basic Graph Patterns over Dynamic Link Data Graphs

In this paper, we investigate the problem of evaluating Basic Graph Patterns (BGP, for short, a subclass of SPARQL queries) over dynamic Linked Data graphs; i.e., Linked Data graphs that are continuously updated. We consider a setting where the updates are continuously received through a stream of messages and support both insertions and deletions of triples (updates are straightforwardly handled as a combination of deletions and insertions). In this context, we propose a set of in-memory algorithms minimizing the cached data to efficiently and continuously answer BGP queries. The queries are typically submitted into a system and continuously result in the delta answers while the update messages are processed. To efficiently and continuously evaluate the submitted query over the streaming data, as well as to minimize the amount of cached data, we propose an approach where the submitted query is decomposed into simpler subqueries and the query evaluation is achieved by combining the intermediate answers of the subqueries. Using this approach, the proposed algorithms compute the delta answers of a BGP query in polynomial time and space. Note that for certain subclasses of BGP queries, we show that the evaluation can be achieved in constant or linear time and space. Consolidating all the historical delta answers, the algorithms ensure that the answer to each query is constructed at any given time.

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arXiv2022

Efficient query evaluation techniques over large amount of distributed linked data

As RDF becomes more widely established and the amount of linked data is rapidly increasing, the efficient querying of large amount of data becomes a significant challenge. In this paper, we propose a family of algorithms for querying large amount of linked data in a distributed manner. These query evaluation algorithms are independent of the way the data is stored, as well as of the particular implementation of the query evaluation. We then use the MapReduce paradigm to present a distributed implementation of these algorithms and experimentally evaluate them, although the algorithms could be straightforwardly translated into other distributed processing frameworks. We also investigate and propose multiple query decomposition approaches of Basic Graph Patterns (subclass of SPARQL queries) that are used to improve the overall performance of the distributed query answering. A deep analysis of the effectiveness of these decomposition algorithms is also provided.

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arXiv2021

Querying collections of tree-structured records in the presence of within-record referential constraints

In this paper, we consider a tree-structured data model used in many commercial databases like Dremel, F1, JSON stores. We define identity and referential constraints within each tree-structured record. The query language is a variant of SQL and flattening is used as an evaluation mechanism. We investigate querying in the presence of these constraints, and point out the challenges that arise from taking them into account during query evaluation.

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arXiv2020

On the complexity of query containment and computing certain answers in the presence of ACs

We often add arithmetic to extend the expressiveness of query languages and study the complexity of problems such as testing query containment and finding certain answers in the framework of answering queries using views. When adding arithmetic comparisons, the complexity of such problems is higher than the complexity of their counterparts without them. It has been observed that we can achieve lower complexity if we restrict some of the comparisons in the containing query to be closed or open semi-interval comparisons. Here, focusing a) on the problem of containment for conjunctive queries with arithmetic comparisons (CQAC queries, for short), we prove upper bounds on its computational complexity and b) on the problem of computing certain answers, we find large classes of CQAC queries and views where this problem is polynomial.

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