Submodular Optimization in Location-Based Social Networks by Xuefeng Chen B.E. University of Electronic Science and Technology of China, 2012 M.E. University of Electronic Science and Technology of China, 2015 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE SCHOOL OF Computer Science and Engineering Tuesday 9th March, 2021 All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. c Xuefeng Chen 2021 i Thesis/Dissertation Sheet Surname/Family Name : Xuefeng Given Name/s : Chen Abbreviation for degree as give in the University calendar : PhD Faculty : Engineering School : School of Computer Science and Engineering Thesis Title : Submodular Optimization in Location-Based Social Networks Abstract 350 words maximum: (PLEASE TYPE) In recent years, with the increasing popularity and growth of social networks and mobile devices, the research on location-based social networks (LBSN) has attracted a lot of attention. As an important research topic in LBSN, submodular optimization in location-based social networks (SO-LBSN) has been considered by many studies, because it is useful in applications such as service location selection, marketing, and tourist trip planning. However, due to the rich information in LBSN (e.g., locations, user relationships), various constraints (e.g., spatial constraint, routing constraint) could be specified in LBSN applications, existing methods often fail in solving such problems on SO-LBSN efficiently. In this thesis, we study three typical problems on SO-LBSN, and utilize the location information, the properties of the submodular functions and the constraints to develop efficient algorithms. Firstly, we investigate the problem of maximizing bichromatic reverse k-nearest neighbor in LBSNs. We use a general submodular function to compute the value of influence. We design a hybrid quadtree-grid index to manage the server points and client points and to reduce the kNN computation cost substantially, and propose an optimization technique called “maximal-arc” to improve the efficiency of the influence computation. We also develop both exact and approximation algorithms with guaranteed error bounds. Secondly, we focus on the problem of optimal region search with submodular maximization. We prove that the problem is NP-hard and propose an approximation algorithm AppORS. We also design another algorithm with the same approximation ratio called IAppORS to further improve the effectiveness of AppORS, and present two heuristic methods to implement a key function of IAppORS. Finally, we study the constrained path search with submodular maximization query. We show that answering the query is NP-hard. We first propose a concept called "submodular 훼-dominance" by utilizing the properties of the submodular function, and develop an approximation algorithm based on this concept. By relaxing the submodular 훼-dominance conditions, we design another approximation algorithm with better efficiency that has the same error bound. We also utilize the way of bi-directional path search to further improve the efficiency, and propose a heuristic polynomial algorithm that is efficient yet effective in practice. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents a non-exclusive licence to archive and to make available (including to members of the public) my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known. I acknowledge that I retain all intellectual property rights which subsist in my thesis or dissertation, such as copyright and patent rights, subject to applicable law. I also retain the right to use all or part of my thesis or dissertation in future works (such as articles or books). …………………………………………………………… ……….… 03/03/2021…...………… Signature Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years can be made when submitting the final copies of your thesis to the UNSW Library. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. ii iii ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed …………………………………………….............. Date …………………………………………….............. iv v INCLUSION OF PUBLICATIONS STATEMENT UNSW is supportive of candidates publishing their research results during their candidature as detailed in the UNSW Thesis Examination Procedure. Publications can be used in their thesis in lieu of a Chapter if: • The candidate contributed greater than 50% of the content in the publication and is the “primary author”, ie. the candidate was responsible primarily for the planning, execution and preparation of the work for publication • The candidate has approval to include the publication in their thesis in lieu of a Chapter from their supervisor and Postgraduate Coordinator. • The publication is not subject to any obligations or contractual agreements with a third party that would constrain its inclusion in the thesis Please indicate whether this thesis contains published material or not: This thesis contains no publications, either published or submitted for publication ☐ Some of the work described in this thesis has been published and it has been documented in the relevant Chapters with acknowledgement ☐ This thesis has publications (either published or submitted for publication) ☒ incorporated into it in lieu of a chapter and the details are presented below CANDIDATE’S DECLARATION I declare that: • I have complied with the UNSW Thesis Examination Procedure • where I have used a publication in lieu of a Chapter, the listed publication(s) below meet(s) the requirements to be included in the thesis. Candidate’s Name Signature Date (dd/mm/yy) Xuefeng Chen 03/03/2021 vi POSTGRADUATE COORDINATOR’S DECLARATION I declare that: • the information below is accurate • where listed publication(s) have been used in lieu of Chapter(s), their use complies with the UNSW Thesis Examination Procedure • the minimum requirements for the format of the thesis have been met. PGC’s Name PGC’s Signature Date (dd/mm/yy) Salil Kanhere 03/03/2021 PRIMARY SUPERVISOR’S DECLARATION I declare that: • the information above is accurate • this has been discussed with the PGC and it is agreed that this publication can be included in this thesis in lieu of a Chapter • All of the co-authors of the publication have reviewed the above information and have agreed to its veracity by signing a ‘Co-Author Authorisation’ form. Primary Supervisor’s name Primary Supervisor’s signature Date (dd/mm/yy) Xin Cao 03/03/2021 vii viii ix COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents a non-exclusive licence to archive and to make available (including to members of the public) my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known. I acknowledge that I retain all intellectual property rights which subsist in my thesis or dissertation, such as copyright and patent rights, subject to applicable law. I also retain the right to use all or part of my thesis or dissertation in future works (such as articles or books).’ ‘For any substantial portions of copyright material used in this thesis, written permission for use has been obtained, or the copyright material is removed from the final public version of the thesis.’ Signed ……………………………………………........................... Date ……………………03/03/2021……………… .................... AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis.’ Signed ……………………………………………........................... Date ……………………03/03/2021…………………… .. .......... x xi Abstract In recent years, with the increasing popularity and growth of social networks and mo- bile devices, the research on location-based social networks (LBSN) has attracted a lot of attention. As an important research topic in LBSN, submodular optimization in location- based social networks (SO-LBSN) has been considered by many studies, because it is useful in applications such as service location selection, marketing, and tourist trip plan- ning. However, due to the rich information in LBSN (e.g., locations, user relationships, texts), various constraints (e.g., spatial constraint, routing constraint, connective con- straint) could be specified in LBSN applications, existing methods often fail in solving such problems on SO-LBSN efficiently. In this thesis, we study three typical problems on SO-LBSN,