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Querying the Deep Web: Back to the Foundations

Andrea Calì, Davide Martinenghi, Igor Razgon, Martín Ugarte
2017 Alberto Mendelzon Workshop on Foundations of Data Management  
In this paper we give some fundamental complexity results on the problem of processing conjunctive (select-project-join) queries on relational data with access limitations.  ...  Deep Web data are usually modelled as relations with so-called access limitations, that is, they can be queried only by selecting certain attributes.  ...  Andrea Calí acknowledges partial support by the EPSRC project "Logic-based Integration and Querying of Unindexed Data" (EP/E010865/1)".  ... 
dblp:conf/amw/CaliMRU17 fatcat:yd25obbqungtnkmqkmnv4kqa6u

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

Determining Relevance of Accesses at Runtime (Extended Version) [article]

Michael Benedikt, Georg Gottlob, Pierre Senellart
2011 arXiv   pre-print
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 long-term 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.  ... 
arXiv:1104.0553v3 fatcat:d6ljizgtrnhfnhlbnj2gknmzs4

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  ...  Query containment Expected duration: 10 minutes We address the problem of checking containment of conjunctive queries in the presence access limitations, which is highly relevant in query optimization.  ... 
doi:10.1109/apweb.2010.83 dblp:conf/apweb/CaliM10 fatcat:c2eqo5hj3fe7xocxtda2jnztnu

On the Complexity of Query Answering under Access Limitations: A Computational Formalism

Andrea Calì, Martín Ugarte
2018 Alberto Mendelzon Workshop on Foundations of Data Management  
In this paper we give some fundamental complexity results on the problem of processing conjunctive (select-project-join) queries on relational data with access limitations.  ...  Deep Web data are usually modelled as relations with so-called access limitations, that is, they can be queried only by selecting certain attributes.  ...  Andrea Calí acknowledges partial support by the EP-SRC project "Logic-based Integration and Querying of Unindexed Data" (EP/E010865/1)" as well as from the Birkbeck BEI School Grant "Exposing the Deep  ... 
dblp:conf/amw/CaliU18 fatcat:aj6htb6gdfesfnis7l7p7ohvt4

Querying the deep web

Andrea Calì, Davide Martinenghi
2010 Proceedings of the 13th International Conference on Extending Database Technology - EDBT '10  
Data stored outside Web pages and accessible from the Web, typically through HTML forms, consitute the so-called Deep Web. Such data are of great value, but difficult to query and search.  ...  We illustrate optimizations both at query plan generation time and at runtime, highlighting the role of integrity constraints.  ...  Davide Martinenghi acknowledges support from the "Search Computing" (SeCo) project, funded by the ERC under the 2008 Call for "IDEAS Advanced Grants".  ... 
doi:10.1145/1739041.1739138 dblp:conf/edbt/CaliM10 fatcat:db2zx6oxjbdg3lzkmm5d3lixfm

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.  ...  Martinenghi acknowledges support from Italian PRIN project "New technologies and tools for the integration of Web search services".  ... 
doi:10.1007/978-3-540-87877-3_24 fatcat:g3tihj2l5rh6vpjkmq63tc4w5y

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

Davide Martinenghi
2014 arXiv   pre-print
The field of query answering under access limitations has been broadly investigated in the past.  ...  Access limitations are restrictions in the way in which the tuples of a relation can be accessed.  ...  Query processing under access patterns requires specialized techniques.  ... 
arXiv:1401.0069v2 fatcat:3zz4l4pry5bfjdvp7mz3gs6ghi

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.  ...  It follows that the question of containment of unions of conjunctive queries under limited access patterns (see [9, 17] for the formal definition) can be expressed as the containment of a AGEMDL query  ... 
doi:10.1007/978-3-642-31585-5_11 fatcat:gesfjmuemja6tagvnexl5lxazm

Processing Unions of Conjunctive Queries with Negation under Limited Access Patterns [chapter]

Alan Nash, Bertram Ludäscher
2004 Lecture Notes in Computer Science  
We study the problem of answering queries over sources with limited access patterns.  ...  We characterize the complexity of deciding feasibility for the classes CQ ¬ (conjunctive queries with negation) and UCQ ¬ (unions of CQ ¬ queries): Testing feasibility is just as hard as testing containment  ...  Limited Access Patterns and Feasibility Here we present the basic definitions for source queries with limited access patterns.  ... 
doi:10.1007/978-3-540-24741-8_25 fatcat:ii7ugygeifg6bmlso6fv54t37y

Processing first-order queries under limited access patterns

Alan Nash, Bertram Ludäscher
2004 Proceedings of the twenty-third ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '04  
We study the problem of answering queries over sources with limited access patterns.  ...  Finally, we outline a practical overall strategy for processing first-order queries under limited access patterns.  ...  Acknowledgements We thank Alin Deutsch for valuable discussions on query containment, in particular, the proof of Theorem 1 was done jointly with him.  ... 
doi:10.1145/1055558.1055601 dblp:conf/pods/NashL04 fatcat:osnpl7ayrvhn7j4cz5qjsr2p2y

Combining fuzzy information from multiple systems (extended abstract)

Ronald Fagin
1996 Proceedings of the fifteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems - PODS '96  
The author is also grateful to Eli Upfal for valuable suggestions, and to Laura Haas and Ed Wimmers for detailed comments on a preliminary version of the paper.  ...  For each i, give subsystem i the query Ai under sorted access.  ...  under the query AZ is less than 1 (note that we can find out the value of -y with one sorted access).  ... 
doi:10.1145/237661.237715 dblp:conf/pods/Fagin96 fatcat:3nzztcs7cfb7tfotfetf77xbuq

Checking XPath Expressions for Synchronization, Access Control and Reuse of Query Results on Mobile Clients

Stefan Böttcher, Adelhard Türling
2003 Workshop des GI-Arbeitskreis Mobile Datenbanken und Informationssysteme  
We demonstrate that different applications ranging from access control to transaction synchronization to the reuse of query results have very similar requirements to the evaluation of XPath expressions  ...  Secondly, we describe the treatment of predicate filters which may be used in XPath expressions for queries, access control, and synchronization, and present a fast predicate evaluator for these predicates  ...  The other alternative is to allow arbitrary complex access right predicates and to reject a user's access in situations, where a user query would exceed the time limit given for access control.  ... 
dblp:conf/m-dbis/BottcherT03 fatcat:o34sb77grnefxbipayg6j7hwc4

Querying schemas with access restrictions

Michael Benedikt, Pierre Bourhis, Clemens Ley
2012 Proceedings of the VLDB Endowment  
We show that AccLTL and A-automata can express static analysis problems related to "querying with limited access patterns" that have been studied in the database literature in the past, such as whether  ...  an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return.  ...  In [5] containment under access restrictions is shown to be decidable for conjunctive queries, while [3] studies the complexity of the problem.  ... 
doi:10.14778/2180912.2180916 fatcat:evj6s3yimze57hypjiojl5v6vu

Querying Schemas With Access Restrictions [article]

Michael Benedikt, Pierre Bourhis, Clemens Ley
2012 arXiv   pre-print
We show that AccLTL and A-automata can express static analysis problems related to "querying with limited access patterns" that have been studied in the database literature in the past, such as whether  ...  an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return.  ...  In [5] containment under access restrictions is shown to be decidable for conjunctive queries, while [3] studies the complexity of the problem.  ... 
arXiv:1203.6403v1 fatcat:anafilw2preb3aoamnq542bt5i
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