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: "vocabulary growth in collaborative tagging systems"
  Abstract: We analyze a large-scale snapshot of del.icio.us and investigate how the number of different tags in the system grows as a function of a suitably defined notion of time. We study the temporal evolution of the global vocabulary size, i.e. the number of distinct tags in the entire system, as well as the evolution of local vocabularies, that is the growth of the number of distinct tags used in the context of a given resource or user. In both cases, we find power-law behaviors with exponents smaller than one. Surprisingly, the observed growth behaviors are remarkably regular throughout the entire history of the system and across very different resources being bookmarked. Similar sub-linear laws of growth have been observed in written text, and this qualitative universality calls for an explanation and points in the direction of non-trivial cognitive processes in the complex interaction patterns characterizing collaborative tagging.

Connected through hyperedge HE-1 (induced by source paper "on the estimation and use of statistical modelling in information retrieval"):
  with members:
    - "part of speech based term weighting for information retrieval"
    - "social resilience in online communities the autopsy of friendster"
    - "collaborative thesaurus tagging the wikipedia way"
    - "the structure of broad topics on the web"
    - "search in power law networks"

Connected through hyperedge HE-2 (induced by source paper "how the nature of web services drives vocabulary creation in social tagging"):
  with members:
    - "online popularity and topical interests through the lens of instagram"

Connected through hyperedge HE-3 (induced by source paper "reuse temporal dynamics interest sharing and collaboration in social tagging systems"):
  with members:
    - "towards a model of understanding social search"
    - "collective dynamics of social annotation"
    - "tracking user attention in collaborative tagging communities"

Connected through hyperedge HE-4 (induced by source paper "what is the nature of chinese microblogging unveiling the unique features of tencent weibo"):
  with members:
    - "twitter mood predicts the stock market"

Connected through hyperedge HE-5 (induced by source paper "what is the nature of tencent weibo detect the unique features of tencent users"):
  with members:
    - "twitter mood predicts the stock market"

Connected through hyperedge HE-6 (induced by source paper "heterogeneity and allometric growth of human collaborative tagging behavior"):
  with members:
    - "the accelerating growth of online tagging systems"
    - "feedback loops of attention in peer production"
    - "collective dynamics of social annotation"

Connected through hyperedge HE-7 (induced by source paper "collective dynamics of social annotation"):
  with members:
    - "semantic analysis of tag similarity measures in collaborative tagging systems"
    - "systematic topology analysis and generation using degree correlations"
    - "collaborative tagging and semiotic dynamics"
    - "the structure of collaborative tagging systems"

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.IR(Information Retrieval)