{"type":"ScholarlyArticle","title":"Efficient Community Search over Large Directed Graph: An Augmented Index-based Approach","authors":[{"name":"Yankai Chen","slug":"yankai-chen","given":"Yankai","family":"Chen","affiliation":"Department of Computer Science and Engineering , The Chinese University of Hong Kong"},{"name":"Jie Zhang","slug":"jie-zhang","given":"Jie","family":"Zhang","affiliation":"School of Computer Science and Engineering , Nanyang Technological University"},{"name":"Yixiang Fang","slug":"yixiang-fang","given":"Yixiang","family":"Fang","affiliation":"School of Computer Science and Engineering , The University of New South Wales"},{"name":"Xin Cao","slug":"xin-cao","given":"Xin","family":"Cao","affiliation":"School of Computer Science and Engineering , The University of New South Wales"},{"name":"Irwin King","slug":"irwin-king","given":"Irwin","family":"King","affiliation":"Department of Computer Science and Engineering , The Chinese University of Hong Kong"}],"abstract":"Given a graph G and a query vertex q, the topic of community search (CS), aiming to retrieve a dense subgraph of G containing q, has gained much attention. Most existing works focus on undirected graphs which overlooks the rich information carried by the edge directions. Recently, the problem of community search over directed graphs (or CSD problem) has been studied [Fang et al., 2019b]; it finds a connected subgraph containing q, where the in-degree and out-degree of each vertex within the subgraph are at least k and l, respectively. However, existing solutions are inefficient, especially on large graphs. To tackle this issue, in this paper we propose a novel index called D-Forest, which allows a CSD query to be completed within the optimal time cost. We further propose efficient index construction methods. Extensive experiments on six real large graphs show that our index-based query algorithm is up to two orders of magnitude faster than existing solutions.","doi":"10.24963/ijcai.2020/490","url":"https://ijcai.org/proceedings/2020/490","pdf":"https://ijcai.org/proceedings/2020/0490.pdf","markdown":"https://ijcai.org/proceedings/2020/490.md","bibtex":"https://ijcai.org/proceedings/2020/bibtex/490","volume":{"slug":"2020","title":"Proceedings of the Twenty-Ninth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2020","url":"https://ijcai.org/proceedings/2020/","year":2020,"location":"Yokohama","dates":"January 2021 (postponed from 11-17 July 2020)","editors":"Christian Bessiere","isbn":"978-0-9992411-6-5","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2020"},"section":"Multidisciplinary Topics and Applications","track":"Main track","number":490,"pages":{"first":3544,"last":3550},"keywords":["Multidisciplinary Topics and Applications: Web Analysis of Communities","Data Mining: Big Data, Large-Scale Systems","Data Mining: Mining Graphs, Semi Structured Data, Complex Data"],"videos":[{"label":"Video","url":"https://videos.ijcai20.org/24637/file_24637.m3u8","length_sec":280,"provider":"hls"}],"references":[{"position":1,"raw":"3 Process vertices to create tree nodes. : function BUILDALEVEL(k, l, V l , pre[ ], cur","title":"3 Process vertices to create tree nodes","authors":null,"year":null,"venue":"function BUILDALEVEL(k, l, V l","doi":null,"url":null,"internal_url":null},{"position":2,"raw":"map, P , Ψ) 2: initialize Sv 1 , • • • , Sv i , • • • for vertices v1, • • • , vi, • • • ∈ V l ; : for v ∈ V l do 4: for u ∈ N (v) do 5: if cur[u] > cur[v] then : ru ← Ψ.FIND(u);","title":"initialize Sv 1","authors":null,"year":null,"venue":null,"doi":null,"url":null,"internal_url":null},{"position":3,"raw":"7: p ← map.get(ru.hook); 8: Sv.add(p ), P.delete(p ); 9: V ← ∅; 10: for v ∈ V l do 11: if k = kmax and pre[v] = l then 12: v.parent ← v, v.hook ← v; 13: v.rank ← 0, V .add(v); 14: else Ψ.MAKESET(v); 15: BATCHUNION(V l \\V , cur[ ], Ψ);","title":"V ← ∅; 10: for v ∈ V l do 11: if k = kmax and pre","authors":null,"year":null,"venue":null,"doi":null,"url":null,"internal_url":null},{"position":4,"raw":"for each set Ci ⊆ V l with the same CUF root do 18: p ← create tree node by using l and Ci; 19: P.add(p); 20: for each v ∈ Ci do 21: map.put(v, p); 22: link nodes in Sv with p; 23: Ψ.UPDATECUF(Ci, cur[ ]);","title":"for each set Ci ⊆ V l with the same CUF root do 18: p ← create tree node by using l and Ci","authors":null,"year":null,"venue":"link nodes in Sv with p","doi":null,"url":null,"internal_url":null},{"position":5,"raw":"function BATCHUNION(V , cur[ ], Ψ) 25: for v ∈ V do 26: for u ∈ N (v) do 27: if cur[u]","title":"for v ∈ V do 26: for u ∈ N","authors":null,"year":null,"venue":null,"doi":null,"url":null,"internal_url":null},{"position":6,"raw":"[Andersen and Lang, 2006] R. 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