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: "monadic datalog and the expressive power of languages for web information extraction"
  Abstract: Research on information extraction from Web pages (wrapping) has seen much activity recently (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this paper, we first study monadic datalog over trees as a wrapping language. We show that this simple language is equivalent to monadic second order logic (MSO) in its ability to specify wrappers. We believe that MSO has the right expressiveness required for Web information extraction and propose MSO as a yardstick for evaluating and comparing wrappers. Along the way, several other results on the complexity of query evaluation and query containment for monadic datalog over trees are established, and a simple normal form for this language is presented. Using the above results, we subsequently study the kernel fragment Elog$^-$ of the Elog wrapping language used in the Lixto system (a visual wrapper generator). Curiously, Elog$^-$ exactly captures MSO, yet is easier to use. Indeed, programs in this language can be entirely visually specified.

Connected through hyperedge HE-1 (induced by source paper "monadic datalog containment on trees using the descendant axis"):
  with members:
    - "monadic datalog containment on trees"
    - "a note on monadic datalog on unranked trees"

Connected through hyperedge HE-2 (induced by source paper "node selection query languages for trees"):
  with members:
    - "logics for unranked trees an overview"

Connected through hyperedge HE-3 (induced by source paper "web data extraction applications and techniques"):
  with members:
    - "traveling trends social butterflies or frequent fliers"
    - "the geospatial characteristics of a social movement communication network"
    - "analyzing user behavior across social sharing environments"
    - "clustering memes in social media"
    - "multi domain collaborative filtering"
    - "a large scale community structure analysis in facebook"
    - "intelligent self repairable web wrappers"
    - "design of automatically adaptable web wrappers"

Connected through hyperedge HE-4 (induced by source paper "monadic datalog containment on trees"):
  with members:
    - "a note on monadic datalog on unranked trees"
    - "conjunctive queries over trees"

Connected through hyperedge HE-5 (induced by source paper "a note on monadic datalog on unranked trees"):
  with members:
    - "logics for unranked trees an overview"

Connected through hyperedge HE-6 (induced by source paper "complete axiomatizations of fragments of monadic second order logic on finite trees"):
  with members:
    - "logics for unranked trees an overview"

Connected through hyperedge HE-7 (induced by source paper "the complexity of datalog on linear orders"):
  with members:
    - "datalog and constraint satisfaction with infinite templates"

Connected through hyperedge HE-8 (induced by source paper "monadic datalog over finite structures with bounded treewidth"):
  with members:
    - "the dlv system for knowledge representation and reasoning"
    - "complexity of monadic inf datalog application to temporal logic"

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)