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: "query rewriting and optimization for ontological databases"
  Abstract: Ontological queries are evaluated against a knowledge base consisting of an extensional database and an ontology (i.e., a set of logical assertions and constraints which derive new intensional knowledge from the extensional database), rather than directly on the extensional database. The evaluation and optimization of such queries is an intriguing new problem for database research. In this paper, we discuss two important aspects of this problem: query rewriting and query optimization. Query rewriting consists of the compilation of an ontological query into an equivalent first-order query against the underlying extensional database. We present a novel query rewriting algorithm for rather general types of ontological constraints which is well-suited for practical implementations. In particular, we show how a conjunctive query against a knowledge base, expressed using linear and sticky existential rules, that is, members of the recently introduced Datalog+/- family of ontology languages, can be compiled into a union of conjunctive queries (UCQ) against the underlying database. Ontological query optimization, in this context, attempts to improve this rewriting process so to produce possibly small and cost-effective UCQ rewritings for an input query.

Connected through hyperedge HE-1 (induced by source paper "data complexity and rewritability of ontology mediated queries in metric temporal logic under the event based semantics full version"):
  with members:
    - "querying log data with metric temporal logic"
    - "stream reasoning in temporal datalog"
    - "ontology based data access a study through disjunctive datalog csp and mmsnp"

Connected through hyperedge HE-2 (induced by source paper "the space efficient core of vadalog"):
  with members:
    - "reachability is in dynfo"
    - "sound complete and minimal ucq rewriting for existential rules"

Connected through hyperedge HE-3 (induced by source paper "dichotomies in ontology mediated querying with the guarded fragment"):
  with members:
    - "a dichotomy theorem for nonuniform csps"
    - "rewritability in monadic disjunctive datalog mmsnp and expressive description logics"
    - "extending consequence based reasoning to sriq"
    - "asking the metaquestions in constraint tractability"
    - "querying the guarded fragment"
    - "ontology based data access a study through disjunctive datalog csp and mmsnp"
    - "a dichotomy on the complexity of consistent query answering for atoms with simple keys"
    - "description logic tboxes model theoretic characterizations and rewritability"

Connected through hyperedge HE-4 (induced by source paper "research directions for principles of data management dagstuhl perspectives workshop 16151"):
  with members:
    - "size bounds and query plans for relational joins"
    - "a survey on measuring indirect discrimination in machine learning"
    - "communication steps for parallel query processing"
    - "probabilistic databases with markoviews"
    - "the vc dimension of queries and selectivity estimation through sampling"

Connected through hyperedge HE-5 (induced by source paper "containment for rule based ontology mediated queries"):
  with members:
    - "query answering with transitive and linear ordered data"
    - "querying the guarded fragment"
    - "ontology based data access a study through disjunctive datalog csp and mmsnp"
    - "relational transducers for declarative networking"

Connected through hyperedge HE-6 (induced by source paper "finite model reasoning over existential rules"):
  with members:
    - "knowledge spaces and the completeness of learning strategies"
    - "querying the guarded fragment"
    - "ontology based data access a study through disjunctive datalog csp and mmsnp"
    - "converging to the chase a tool for finite controllability"

Connected through hyperedge HE-7 (induced by source paper "the complexity of ontology based data access with owl 2 ql and bounded treewidth queries"):
  with members:
    - "tree like queries in owl 2 ql succinctness and complexity results"
    - "acyclicity notions for existential rules and their application to query answering in ontologies"
    - "sound complete and minimal ucq rewriting for existential rules"
    - "exponential lower bounds and separation for query rewriting"

Connected through hyperedge HE-8 (induced by source paper "the pragmatic proof hypermedia api composition and execution"):
  with members:
    - "n3logic a logical framework for the world wide web"

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)