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 study on altering postgresql from multi processes structure to multi threads structure"
  Abstract: How to altering PostgreSQL database from multi-processes structure to multi-threads structure is a difficult problem. In the paper, we bring forward a comprehensive alteration scheme. Especially, put rational methods to account for three difficult points: semaphores, signal processing and global variables. At last, applied the scheme successfully to modify a famous open source DBMS.

Connected through hyperedge HE-1 (induced by source paper "duplication of windows services"):
  with members:
    - "design and implementation of a network security management system"
    - "virtualizing system and ordinary services in windows based os level virtual machines"
    - "implementing rbac model in an operating system kernel"
    - "suspicious taint based access control for protecting os from network attacks"
    - "compatible and usable mandatory access control for good enough os security"

Connected through hyperedge HE-2 (induced by source paper "design and implementation of a network security management system"):
  with members:
    - "virtualizing system and ordinary services in windows based os level virtual machines"
    - "implementing rbac model in an operating system kernel"
    - "suspicious taint based access control for protecting os from network attacks"
    - "compatible and usable mandatory access control for good enough os security"

Connected through hyperedge HE-3 (induced by source paper "confining windows inter process communications for os level virtual machine"):
  with members:
    - "design and implementation of a network security management system"
    - "virtualizing system and ordinary services in windows based os level virtual machines"
    - "implementing rbac model in an operating system kernel"
    - "suspicious taint based access control for protecting os from network attacks"

Connected through hyperedge HE-4 (induced by source paper "suspicious taint based access control for protecting os from network attacks"):
  with members:
    - "design and implementation of a network security management system"
    - "virtualizing system and ordinary services in windows based os level virtual machines"
    - "implementing rbac model in an operating system kernel"
    - "compatible and usable mandatory access control for good enough os security"

Connected through hyperedge HE-5 (induced by source paper "virtualizing system and ordinary services in windows based os level virtual machines"):
  with members:
    - "design and implementation of a network security management system"
    - "implementing rbac model in an operating system kernel"
    - "suspicious taint based access control for protecting os from network attacks"

Connected through hyperedge HE-6 (induced by source paper "implementing rbac model in an operating system kernel"):
  with members:
    - "design and implementation of a network security management system"

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)