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: "foundations of sparql query optimization"
  Abstract: The SPARQL query language is a recent W3C standard for processing RDF data, a format that has been developed to encode information in a machine-readable way. We investigate the foundations of SPARQL query optimization and (a) provide novel complexity results for the SPARQL evaluation problem, showing that the main source of complexity is operator OPTIONAL alone; (b) propose a comprehensive set of algebraic query rewriting rules; (c) present a framework for constraint-based SPARQL optimization based upon the well-known chase procedure for Conjunctive Query minimization. In this line, we develop two novel termination conditions for the chase. They subsume the strongest conditions known so far and do not increase the complexity of the recognition problem, thus making a larger class of both Conjunctive and SPARQL queries amenable to constraint-based optimization. Our results are of immediate practical interest and might empower any SPARQL query optimizer.

Connected through hyperedge HE-1 (induced by source paper "towards an integrated graph algebra for graph pattern matching with gremlin extended version"):
  with members:
    - "a stitch in time saves nine sparql querying of property graphs using gremlin traversals"
    - "the multiset semantics of sparql patterns"
    - "foundations of modern query languages for graph databases"
    - "the gremlin graph traversal machine and language invited talk"
    - "a path algebra for multi relational graphs"
    - "the graph traversal pattern"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-2 (induced by source paper "certain answers to a sparql query over a knowledge base extended version"):
  with members:
    - "on tractable query evaluation for sparql"
    - "the dl lite family and relations"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-3 (induced by source paper "subsumption of weakly well designed sparql patterns is undecidable"):
  with members:
    - "semantics and complexity of sparql"

Connected through hyperedge HE-4 (induced by source paper "sage web preemption for public sparql query services"):
  with members:
    - "semantics and complexity of sparql"

Connected through hyperedge HE-5 (induced by source paper "a stitch in time saves nine sparql querying of property graphs using gremlin traversals"):
  with members:
    - "killing two birds with one stone querying property graphs using sparql via gremlinator"
    - "the multiset semantics of sparql patterns"
    - "a formal graph model for rdf and its implementation"
    - "the gremlin graph traversal machine and language invited talk"
    - "the graph traversal pattern"
    - "sp2bench a sparql performance benchmark"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-6 (induced by source paper "killing two birds with one stone querying property graphs using sparql via gremlinator"):
  with members:
    - "a stitch in time saves nine sparql querying of property graphs using gremlin traversals"
    - "the gremlin graph traversal machine and language invited talk"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-7 (induced by source paper "gsmat a scalable sparse matrix based join for sparql query processing"):
  with members:
    - "tripleid q rdf query processing framework using gpu"
    - "taming subgraph isomorphism for rdf query processing"
    - "semantics and complexity of sparql"

Connected through hyperedge HE-8 (induced by source paper "algorithms and analysis for the sparql constructs"):
  with members:
    - "on the statistical analysis of practical sparql queries"
    - "semantics and complexity of sparql"

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)