human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "hypertree decompositions and tractable queries"
  Abstract: Several important decision problems on conjunctive queries (CQs) are NP-complete in general but become tractable, and actually highly parallelizable, if restricted to acyclic or nearly acyclic queries. Examples are the evaluation of Boolean CQs and query containment. These problems were shown tractable for conjunctive queries of bounded treewidth (Ch. Chekuri and A. Rajaraman, Theoret. Comput. Sci.239 (2000), 211?229), and of bounded degree of cyclicity (M. Gyssens et al., Artif. Intell.66 (1994), 57?89; M. Gyssens and J. Paredaens, in “Advances in Database Theory, Vol. 2, pp. 85?122, Plenum Press, New York, 1984). The so far most general concept of nearly acyclic queries was the notion of queries of bounded query-width introduced by Chekuri and Rajaraman (2000). While CQs of bounded query-width are tractable, it remained unclear whether such queries are efficiently recognizable. Chekuri and Rajaraman (2000) stated as an open problem whether for each constant k it can be determined in polynomial time if a query has query-width at most k. We give a negative answer by proving the NP-completeness of this problem (specifically, for k=4). In order to circumvent this difficulty, we introduce the new concept of hypertree decomposition of a query and the corresponding notion of hypertree-width. We prove: (a) for each k, the class of queries with query-width bounded by k is properly contained in the class of queries whose hypertree-width is bounded by k; (b) unlike query-width, constant hypertree-width is efficiently recognizable; and (c) Boolean queries of bounded hypertree-width can be efficiently evaluated.

Connected through hyperedge HE-1 (induced by source paper "complexity analysis of general and fractional hypertree decompositions"):
  with members:
    - "hyperbench a benchmark and tool for hypergraphs and empirical findings"
    - "tree projections and constraint optimization problems fixed parameter tractability and parallel algorithms"
    - "size bounds and query plans for relational joins"
    - "constraint solving via fractional edge covers"
    - "an analytical study of large sparql query logs"
    - "old techniques for new join algorithms a case study in rdf processing"
    - "general and fractional hypertree decompositions hard and easy cases"
    - "myhill nerode methods for hypergraphs"

Connected through hyperedge HE-2 (induced by source paper "constant delay enumeration with fpt preprocessing for conjunctive queries of bounded submodular width"):
  with members:
    - "enumeration on trees under relabelings"
    - "answering fo mod queries under updates on bounded degree databases"
    - "covers of query results"
    - "constraint solving via fractional edge covers"
    - "answering conjunctive queries under updates"
    - "compressed representations of conjunctive query results"
    - "answering ucqs under updates and in the presence of integrity constraints"
    - "what do shannon type inequalities submodular width and disjunctive datalog have to do with one another"

Connected through hyperedge HE-3 (induced by source paper "querying guarded fragments via resolution"):
  with members:
    - "deciding the loosely guarded fragment and querying its horn fragment using resolution"
    - "querying the guarded fragment"

Connected through hyperedge HE-4 (induced by source paper "optimal algorithms for ranked enumeration of answers to full conjunctive queries"):
  with members:
    - "ranked enumeration of conjunctive query results"
    - "any k anytime top k tree pattern retrieval in labeled graphs"
    - "on functional aggregate queries with additive inequalities"
    - "on the enumeration complexity of unions of conjunctive queries"
    - "size bounds and query plans for relational joins"
    - "covers of query results"
    - "constraint solving via fractional edge covers"
    - "answering conjunctive queries under updates"

Connected through hyperedge HE-5 (induced by source paper "a join based hybrid parameter for constraint satisfaction"):
  with members:
    - "binary constraint satisfaction problems defined by excluded topological minors"
    - "size bounds and query plans for relational joins"
    - "constraint solving via fractional edge covers"
    - "what do shannon type inequalities submodular width and disjunctive datalog have to do with one another"
    - "general and fractional hypertree decompositions hard and easy cases"
    - "faq questions asked frequently"
    - "tractable hypergraph properties for constraint satisfaction and conjunctive queries"
    - "using pivot consistency to decompose and solve functional csps"

Connected through hyperedge HE-6 (induced by source paper "a more general theory of static approximations for conjunctive queries"):
  with members:
    - "constraint solving via fractional edge covers"
    - "semantic acyclicity under constraints"
    - "general and fractional hypertree decompositions hard and easy cases"
    - "decidability results for the boundedness problem"
    - "querying the guarded fragment"
    - "beyond hypertree width decomposition methods without decompositions"

Connected through hyperedge HE-7 (induced by source paper "solving linear programs on factorized databases"):
  with members:
    - "ranked enumeration of conjunctive query results"
    - "general and fractional hypertree decompositions hard and easy cases"
    - "efficient inverse maintenance and faster algorithms for linear programming"
    - "aggregation in probabilistic databases via knowledge compilation"
    - "combining relational algebra sql constraint modelling and local search"

Connected through hyperedge HE-8 (induced by source paper "dependency weighted aggregation on factorized databases"):
  with members:
    - "constraint solving via fractional edge covers"
    - "hypergraph acyclicity and propositional model counting"
    - "gym a multiround join algorithm in mapreduce"
    - "structural tractability of counting of solutions to conjunctive queries"
    - "a knowledge compilation map"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.DB(Databases)