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: "aggregations over generalized hypertree decompositions"
  Abstract: We study a class of aggregate-join queries with multiple aggregation operators evaluated over annotated relations. We show that straightforward extensions of standard multiway join algorithms and generalized hypertree decompositions (GHDs) provide best-known runtime guarantees. In contrast, prior work uses bespoke algorithms and data structures and does not match these guarantees. Our extensions to the standard techniques are a pair of simple tests that (1) determine if two orderings of aggregation operators are equivalent and (2) determine if a GHD is compatible with a given ordering. These tests provide a means to find an optimal GHD that, when provided to standard join algorithms, will correctly answer a given aggregate-join query. The second class of our contributions is a pair of complete characterizations of (1) the set of orderings equivalent to a given ordering and (2) the set of GHDs compatible with some equivalent ordering. We show by example that previous approaches are incomplete. The key technical consequence of our characterizations is a decomposition of a compatible GHD into a set of (smaller) {\em unconstrained} GHDs, i.e. into a set of GHDs of sub-queries without aggregations. Since this decomposition is comprised of unconstrained GHDs, we are able to connect to the wide literature on GHDs for join query processing, thereby obtaining improved runtime bounds, MapReduce variants, and an efficient method to find approximately optimal GHDs.

Connected through hyperedge HE-1 (induced by source paper "memory efficient group by aggregates over multi way joins"):
  with members:
    - "ac dc in database learning thunderstruck"
    - "on functional aggregate queries with additive inequalities"
    - "covers of query results"
    - "boolean tensor decomposition for conjunctive queries with negation"
    - "worst case optimal algorithms for parallel query processing"
    - "faq questions asked frequently"
    - "skew strikes back new developments in the theory of join algorithms"
    - "leapfrog triejoin a worst case optimal join algorithm"

Connected through hyperedge HE-2 (induced by source paper "tree projections and constraint optimization problems fixed parameter tractability and parallel algorithms"):
  with members:
    - "constraint solving via fractional edge covers"
    - "greedy strategies and larger islands of tractability for conjunctive queries and constraint satisfaction problems"
    - "general and fractional hypertree decompositions hard and easy cases"
    - "faq questions asked frequently"
    - "structural tractability of enumerating csp solutions"
    - "a quasi polynomial time partition oracle for graphs with an excluded minor"
    - "possibilistic constraint satisfaction problems or how to handle soft constraints"
    - "tree projections and structural decomposition methods minimality and game theoretic characterization"

Connected through hyperedge HE-3 (induced by source paper "flexible caching in trie joins"):
  with members:
    - "join processing for graph patterns an old dog with new tricks"
    - "emptyheaded boolean algebra based graph processing"
    - "faq questions asked frequently"
    - "aggregation and ordering in factorised databases"
    - "skew strikes back new developments in the theory of join algorithms"
    - "hypertree decompositions and tractable queries"

Connected through hyperedge HE-4 (induced by source paper "old techniques for new join algorithms a case study in rdf processing"):
  with members:
    - "size bounds and query plans for relational joins"
    - "emptyheaded a relational engine for graph processing"
    - "taming subgraph isomorphism for rdf query processing"

Connected through hyperedge HE-5 (induced by source paper "emptyheaded a relational engine for graph processing"):
  with members:
    - "size bounds and query plans for relational joins"
    - "snap a general purpose network analysis and graph mining library"
    - "join processing for graph patterns an old dog with new tricks"
    - "faq questions asked frequently"
    - "simd compression and the intersection of sorted integers"
    - "eagr supporting continuous ego centric aggregate queries over large dynamic graphs"
    - "gym a multiround join algorithm in mapreduce"
    - "skew strikes back new developments in the theory of join algorithms"

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)