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: "efficient skyline querying with variable user preferences on nominal attributes"
  Abstract: Current skyline evaluation techniques assume a fixed ordering on the attributes. However, dynamic preferences on nominal attributes are more realistic in known applications. In order to generate online response for any such preference issued by a user, we propose two methods of different characteristics. The first one is a semi-materialization method and the second is an adaptive SFS method. Finally, we conduct experiments to show the efficiency of our proposed algorithms.

Connected through hyperedge HE-1 (induced by source paper "eclipse generalizing knn and skyline"):
  with members:
    - "eclipse practicability beyond 1nn and skyline"
    - "preference elicitation in prioritized skyline queries"

Connected through hyperedge HE-2 (induced by source paper "continuous monitoring of pareto frontiers on partially ordered attributes for many users"):
  with members:
    - "optimal aggregation algorithms for middleware"

Connected through hyperedge HE-3 (induced by source paper "eclipse practicability beyond 1nn and skyline"):
  with members:
    - "preference elicitation in prioritized skyline queries"

Connected through hyperedge HE-4 (induced by source paper "a survey of skyline query processing"):
  with members:
    - "worst case background knowledge for privacy preserving data publishing"

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)