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: "a trichotomy for regular simple path queries on graphs"
  Abstract: Regular path queries (RPQs) select nodes connected by some path in a graph. The edge labels of such a path have to form a word that matches a given regular expression. We investigate the evaluation of RPQs with an additional constraint that prevents multiple traversals of the same nodes. Those regular simple path queries (RSPQs) find several applications in practice, yet they quickly become intractable, even for basic languages such as (aa)* or a*ba*. #R##N#In this paper, we establish a comprehensive classification of regular languages with respect to the complexity of the corresponding regular simple path query problem. More precisely, we identify the fragment that is maximal in the following sense: regular simple path queries can be evaluated in polynomial time for every regular language L that belongs to this fragment and evaluation is NP-complete for languages outside this fragment. We thus fully characterize the frontier between tractability and intractability for RSPQs, and we refine our results to show the following trichotomy: Evaluations of RSPQs is either AC0, NL-complete or NP-complete in data complexity, depending on the regular language L. The fragment identified also admits a simple characterization in terms of regular expressions. #R##N#Finally, we also discuss the complexity of the following decision problem: decide, given a language L, whether finding a regular simple path for L is tractable. We consider several alternative representations of L: DFAs, NFAs or regular expressions, and prove that this problem is NL-complete for the first representation and PSPACE-complete for the other two. As a conclusion we extend our results from edge-labeled graphs to vertex-labeled graphs and vertex-edge labeled graphs.

Connected through hyperedge HE-1 (induced by source paper "regular expressions with backreferences polynomial time matching techniques"):
  with members:
    - "deterministic regular expressions with back references"

Connected through hyperedge HE-2 (induced by source paper "an analytical study of large sparql query logs"):
  with members:
    - "gmark schema driven generation of graphs and queries"
    - "enumeration problems for regular path queries"
    - "old techniques for new join algorithms a case study in rdf processing"
    - "on the statistical analysis of practical sparql queries"
    - "flexible caching in trie joins"
    - "an empirical study of real world sparql queries"
    - "semantics and complexity of sparql"
    - "hypertree decompositions and tractable queries"

Connected through hyperedge HE-3 (induced by source paper "clique width and directed width measures for answer set programming"):
  with members:
    - "directed width measures and monotonicity of directed graph searching"
    - "digraph complexity measures and applications in formal language theory"
    - "backdoors to tractable answer set programming"
    - "trichotomy and dichotomy results on the complexity of reasoning with disjunctive logic programs"
    - "fixed parameter complexity of semantics for logic programs"
    - "a hierarchy of tractable subsets for computing stable models"

Connected through hyperedge HE-4 (induced by source paper "foundations of modern query languages for graph databases"):
  with members:
    - "the multiset semantics of sparql patterns"
    - "graphite an extensible graph traversal framework for relational database management systems"
    - "nested regular path queries in description logics"
    - "a general framework for representing reasoning and querying with annotated semantic web data"
    - "foundations of sparql query optimization"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-5 (induced by source paper "directed width measures and monotonicity of directed graph searching"):
  with members:
    - "graph searching parity games and imperfect information"
    - "digraph decompositions and monotonicity in digraph searching"

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)