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Determining Relevant Relations for Datalog Queries under Access Limitations is Undecidable [article]

Davide Martinenghi
2014 arXiv   pre-print
In this short paper, we show that relevance is undecidable for Datalog queries.  ...  Attention has been devoted to the problem of determining relations that are relevant for a query, i.e., those (possibly off-query) relations that might need to be accessed in order to find all tuples in  ...  Testing relevance for Datalog queries is undecidable. Proof. Let Π be a Datalog program over a schema R, without access limitations, defining two arbitrary predicates p and q.  ... 
arXiv:1401.0069v2 fatcat:3zz4l4pry5bfjdvp7mz3gs6ghi

Querying schemas with access restrictions

Michael Benedikt, Pierre Bourhis, Clemens Ley
2012 Proceedings of the VLDB Endowment  
an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return.  ...  An access is a lookup on a relation within a relational database, fixing values for a set of positions in the relation.  ...  An example is the work in [3] which proposes limiting the number of accesses to be explored by determining that some accesses are not "relevant" to a query.  ... 
doi:10.14778/2180912.2180916 fatcat:evj6s3yimze57hypjiojl5v6vu

Querying Schemas With Access Restrictions [article]

Michael Benedikt, Pierre Bourhis, Clemens Ley
2012 arXiv   pre-print
an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return.  ...  An access is a lookup on a relation within a relational database, fixing values for a set of positions in the relation.  ...  An example is the work in [3] which proposes limiting the number of accesses to be explored by determining that some accesses are not "relevant" to a query.  ... 
arXiv:1203.6403v1 fatcat:anafilw2preb3aoamnq542bt5i

Analysis of Schemas with Access Restrictions

Michael Benedikt, Pierre Bourhis, Clemens Ley
2015 ACM Transactions on Database Systems  
an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return.  ...  An access is a lookup on a relation within a relational database, fixing values for a set of positions in the relation.  ...  An example is the work in [Benedikt et al. 2011 ] which proposes limiting the number of accesses to be explored by determining that some accesses are not "relevant" to a query.  ... 
doi:10.1145/2699500 fatcat:2tqqfy4zr5c3nlgsdvl3z2mlau

Complexity of answering queries using materialized views

Serge Abiteboul, Oliver M. Duschka
1998 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems - PODS '98  
The languages we consider for view definitions and user queries are: conjunctive queries with inequality, positive queries, datalog, and first-order logic.  ...  We study the complexity of the problem of answering queries using materialized views. This problem has attracted a lot of attention recently because of its relevance in data integration.  ...  Levy for pointing us to the work of Ron van der Meyden on the complexity of querying indefinite databases, and Michael R.  ... 
doi:10.1145/275487.275516 dblp:conf/pods/AbiteboulD98 fatcat:sylli5hzgrenvhni4d3y4stise

Conjunctive Query Containment under Access Limitations [chapter]

Andrea Calì, Davide Martinenghi
2008 Lecture Notes in Computer Science  
We address the problem of checking containment of conjunctive queries under access limitations, which is highly relevant in query optimization.  ...  It is known that evaluating a conjunctive query under such access restrictions amounts to evaluating a possibly recursive Datalog program.  ...  Calì was supported by the EPSRC project "Schema Mappings and Automated Services for Data Integration and Exchange" (EP/E010865/1). D.  ... 
doi:10.1007/978-3-540-87877-3_24 fatcat:g3tihj2l5rh6vpjkmq63tc4w5y

Optimizing Query Processing for the Hidden Web

Andrea Calì, Davide Martinenghi
2010 2010 12th International Asia-Pacific Web Conference  
In this tutorial, we illustrate the semantics of answers to queries over data sources under access limitations and present techniques for querying answering in this context.  ...  Besides data accessible through web forms, access limitations may also occur i) in legacy systems where data scattered over several files are wrapped as relational tables, and ii) in the context of Web  ...  In the tutorial, we will discuss several open issues related with the above mentioned techniques for query processing under access limitations.  ... 
doi:10.1109/apweb.2010.83 dblp:conf/apweb/CaliM10 fatcat:c2eqo5hj3fe7xocxtda2jnztnu

Queries with guarded negation

Vince Bárány, Balder ten Cate, Martin Otto
2012 Proceedings of the VLDB Endowment  
Many basic problems are decidable and admit practical algorithms in the case of unions of conjunctive queries, but become difficult or even undecidable when queries are allowed to contain negation.  ...  GN-SQL and GN-Datalog subsume a number of well known query languages and constraint languages, such as unions of conjunctive queries, monadic Datalog, and frontier-guarded tgds.  ...  We thank Alkis Polyzotis for helpful comments. Detailed proofs of the results can be found at http://tiny.cc/guardednegation.  ... 
doi:10.14778/2350229.2350250 fatcat:aripunuyezfhrpdaslsci3lspu

How Can Reasoners Simplify Database Querying (And Why Haven't They Done It Yet)?

Michael Benedikt
2018 Proceedings of the 35th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems - SIGMOD/PODS '18  
The purpose of this article is to reflect on the use of reasoning for rewriting and simplifying relational database queries.  ...  We undertake a review of some of the results and reasoning algorithms that have been developed with a motivation from query evaluation, and add to this a look at open problems in the area as well as a  ...  I want to express my deep gratitude to Marcelo Arenas, Michaël Cadilhac, Phokion Kolaitis, Dan Olteanu, and Victor Vianu for extensive feedback on this work.  ... 
doi:10.1145/3196959.3196989 dblp:conf/pods/Benedikt18 fatcat:fmx4gidgbzb6fpxtvrsy4eyskm

Monadic Datalog Containment [chapter]

Michael Benedikt, Pierre Bourhis, Pierre Senellart
2012 Lecture Notes in Computer Science  
We reconsider the problem of containment of monadic datalog (MDL) queries in unions of conjunctive queries (UCQs).  ...  We then present a general approach for getting tighter bounds on the complexity, based on analysis of the number of mappings of queries into tree-like instances.  ...  Bourhis is supported by EPSRC EP/G004021/1 (the Engineering and Physical Sciences Research Council, UK). Senellart is partly supported by ERC grant Webdam, agreement 226513.  ... 
doi:10.1007/978-3-642-31585-5_11 fatcat:gesfjmuemja6tagvnexl5lxazm

Queries with Guarded Negation (full version) [article]

Vince Barany, Balder ten Cate, Martin Otto
2012 arXiv   pre-print
Many basic problems are decidable and admit practical algorithms in the case of unions of conjunctive queries, but become difficult or even undecidable when queries are allowed to contain negation.  ...  GN-SQL and GN-Datalog subsume a number of well known query languages and constraint languages, such as unions of conjunctive queries, monadic Datalog, and frontier-guarded tgds.  ...  We also determine the complexity of query evaluation for queries with guarded negation, which (under reasonable complexity theoretic assumptions) is easier than the same problem for queries with unguarded  ... 
arXiv:1203.0077v1 fatcat:bdcauk25nffedhieb74vtalnrq

Determining relevance of accesses at runtime

Michael Benedikt, Georg Gottlob, Pierre Senellart
2011 Proceedings of the 30th symposium on Principles of database systems of data - PODS '11  
In the process, we relate dynamic relevance of an access to query containment under access limitations and characterize the complexity of this problem; we produce several complexity results about containment  ...  We consider immediate and longterm notions of "relevant accesses", and ascertain the complexity of query relevance, for both conjunctive queries and arbitrary positive queries.  ...  We thank Pierre Bourhis for great assistance with an earlier draft of the paper.  ... 
doi:10.1145/1989284.1989309 dblp:conf/pods/BenediktGS11 fatcat:rzg6skwyzvcgzhjyznydnoc56a

Win-move is coordination-free (sometimes)

Daniel Zinn, Todd J. Green, Bertram Ludäscher
2012 Proceedings of the 15th International Conference on Database Theory - ICDT '12  
In this paper, we present three additional models for declarative networking. In these variants, relational transducers have limited access to the way data is distributed.  ...  Indeed, Ameloot et al. [9] showed that a query can be computed by a coordination-free relational transducer network iff it is monotone, thus answering in the affirmative a variant of Hellerstein's CALM  ...  Theorem 4.7 Under the disorderly semantics, functionality, termination, and eventual consistency are undecidable for Datalog ¬¬ ∀ , even for programs without universal quantification or eidb relations.  ... 
doi:10.1145/2274576.2274588 dblp:conf/icdt/ZinnGL12 fatcat:dtdthuubtjbjhmuel7limzjjua

Query Processing in Data Integration

Paolo Guagliardo, Piotr Wieczorek, Marc Herbstritt
2013 Dagstuhl Publications  
A rewriting Q r ∈ L r of a query Q ∈ L q under sound views V is L r -maximal iff, there is no rewriting Q r ∈ L r of Q under V such that, for some V-extension E which is sound w.r.t. some database D, it  ...  A rewriting Q r ∈ L r of a query Q ∈ L q under exact views V is L r -maximal iff, there exists no rewriting Q r ∈ L r of Q under V such that Q r V R (D) ⊃ Q r V R (D) for some database D.  ...  Here, the problem of checking whether there exists an exact rewriting for a datalog query reduces to the datalog query containment [33] which is undecidable [53] .  ... 
doi:10.4230/dfu.vol5.10452.129 dblp:conf/dagstuhl/GuagliardoW13 fatcat:2bqbnhu3wbe3rcvsck6aqzr3em

Query containment for data integration systems

Todd Millstein, Alon Levy, Marc Friedman
2000 Proceedings of the nineteenth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '00  
Surprisingly, we show that relative containment for conjunctive queries is still decidable in this case, even though it is known that finding all answers to such queries may require a recursive datalog  ...  The problem of query containment is fundamental to many aspects of database systems, including query optimization, determining independence of queries from updates, and rewriting queries using views.  ...  Therefore, determining query containment of the datalog programs created for the two queries also determines containment of the queries relative to the views.  ... 
doi:10.1145/335168.335208 dblp:conf/pods/MillsteinLF00 fatcat:7f6ird7hjvdrtaujbcs7rn23nm
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