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    <article-meta>
      <title-group>
        <article-title>A Proposal for Improving Project Coordination using Data Mining and Proximity Tracking Elizabeth Bjarnason and Håkan Jonsson</article-title>
      </title-group>
      <contrib-group>
        <aff id="aff0">
          <label>0</label>
          <institution>Lund University</institution>
          ,
          <country country="SE">Sweden</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Coordination is an important success factor for a development project. Communication gaps, e.g. between product owners shaping the requirements and testers verifying the developed software can result in wasted effort and unsuccessful products. We propose improving the communication between project members with recommendations of whom to interact with and what to discuss based on link prediction in multi-layered proximity-based social graphs based on data mined from project repositories. We plan to explore and validate these ideas through prototyping and by applying a design-science approach in collaboration with an industrial partner.</p>
      </abstract>
      <kwd-group>
        <kwd>communication</kwd>
        <kwd>data mining</kwd>
        <kwd>social networks</kwd>
        <kwd>machine learning</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>Introduction</title>
      <p>
        Developing software is a knowledge-intense activity that greatly relies on
communication [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ]. Development projects struggle with information overload [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ] and managing
huge amounts of complex and ever-changing information spread over multiple roles
and repositories, e.g. requirements- and test-management systems. Time is wasted on
locating relevant information [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ], and coordinating a project is a challenge [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4</xref>
        ].
      </p>
      <p>
        Distances between individuals and teams can negatively affect communication
frequency and quality [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. Apart from physical distance that reduces the rate of direct
communication [
        <xref ref-type="bibr" rid="ref1 ref4">1, 4</xref>
        ], there are also cognitive and psychological distances that can
cause communication gaps and misunderstandings. Good communication practices
address distances and improve coordination [
        <xref ref-type="bibr" rid="ref18 ref3 ref5">3, 5, 18</xref>
        ]. The information flow can be
enhanced by collaboration tools that improve artefact navigation [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ] and awareness of
ongoing activities [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ]. Furthermore, identifying communication patterns can enable
improving the communication and even predict the risk of quality issues [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ].
      </p>
      <p>In this short paper, we outline an idea for improving project collaboration and
requirements communication by a conversation recommendation application that
prompts, e.g. a product owner and a tester to discuss related issue reports and
requirements. The recommendations are based on data mined from project repositories and
from tracking people’s physical interaction and proximity with others. The approach
could support requirements coordination in larger projects for the following scenarios:</p>
      <p>Interaction Recommendations. When users are in close proximity to each other
the application identifies related tasks associated with these users, and suggests a
conversation around these, e.g. similar requirements, issues reports or test cases.</p>
      <p>Coordination Recommendations. A user is provided with recommendations on
who to coordinate with based on related tasks and previous physical encounters. For
example, a product owner is prompted to contact a certain tester whom is defining test
cases related to requirements currently discussed with a customer.</p>
      <p>Orientation of New Team Member. A new tester can browse other team members
and their tasks and those related to her tasks are highlighted, thus indicating possible
sources of requirements information.</p>
      <p>Project Meeting Support. The application can provide a list of items for the
detected participants to discuss based on their ongoing tasks, thus highlighting current
requirements topics. The application can also outline meeting notes containing the
proposed topics and the set of participants.</p>
      <p>
        Human resource management. Managers can use the application to identify key
resources in their organisation. For example, individuals that are critical to the
requirements-test coordination in the organisation, so called information brokers [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ].
      </p>
      <sec id="sec-1-1">
        <title>Organisation and office space management. The application can detect which</title>
        <p>people and teams that interact, or should interact, on a regular basis, and can suggest
how to organise the staff and how to plan office space. For example, place product
owners close to the teams and testers that they frequently interact with.</p>
        <p>Related work is described in Section 2. We outline our proposal in Section 3 and our
future plans in Section 4.
2</p>
      </sec>
    </sec>
    <sec id="sec-2">
      <title>Background and Related Work</title>
      <p>Our research proposal is based on providing recommendations derived from
information about connections between project members. This information consists of
physical proximity, information derived from mining various computer systems used by
these engineers, and connections between the artefacts stored in these systems
identified by natural language processing techniques.
2.1</p>
      <sec id="sec-2-1">
        <title>Supporting Direct Interaction with Physical Proximity Tracking</title>
        <p>Tracking people’s physical location, and their proximity to others and to devices poses
interesting possibilities. Proximity tracking has been researched in the context of social
contacts (e.g. Facebook) and software development teams. In both cases Bluetooth via
mobile phones was used due to not requiring additional communication infrastructure.</p>
        <p>
          Eagle and Pentland deployed the first system in an office setting using mobile phones
for proximity sensing with the purpose of introducing serendipitous contact formation
[
          <xref ref-type="bibr" rid="ref9">9</xref>
          ]. Similarity of user profiles was used to recommend people to connect to.
        </p>
        <p>
          Corral et al. used proximity measures to track and identify software engineering
activities through the use of a mobile application and tagging of physical devices [
          <xref ref-type="bibr" rid="ref7">7</xref>
          ], e.g.
computers with Bluetooth dongles. Corral et al. identified work sessions from this
proximity data through detection of patterns for, e.g. pair programming.
        </p>
        <p>
          Similarly Jonsson and Nugues used Bluetooth-enabled mobile phones to capture
meeting participation based on proximity to others and/or to a room-specific mobile
phone [
          <xref ref-type="bibr" rid="ref12">12</xref>
          ]. The participants’ social identities were used through a features of the
Proximates system [
          <xref ref-type="bibr" rid="ref12">12</xref>
          ]. Proximates matches a physical device’s identifier (BT MAC id)
with user identities of, e.g. Facebook, and provides functionality for scanning and
logging interactions. These features were also applied in a reminder application [
          <xref ref-type="bibr" rid="ref13">13</xref>
          ] that
prompts the user when in physical proximity to social contacts for which a reminder
has been set, e.g. repay loan, discuss holiday plans etc.
        </p>
        <p>Discussion. Physical proximity is a very promising concept for tracking engineers’
direct interactions including one-to-one and group meetings. The Proximates
functionality would enable connecting the user of a mobile phone to information found in
software engineering repositories, e.g. issues and tasks currently assigned to this person.
The ability to identify meeting participants could be used to detect and monitor
important interaction and communication points for a project.
2.2</p>
      </sec>
      <sec id="sec-2-2">
        <title>Identifying Communication Patterns with Social Network Analysis</title>
        <p>
          Mining and analysis of social networks is an active research topic that is used for
several applications including prioritisation of e-mails [
          <xref ref-type="bibr" rid="ref21">21</xref>
          ] and enhancing collaboration
[
          <xref ref-type="bibr" rid="ref20 ref8">8, 20</xref>
          ]. Social networks have been constructed from sources such as e-mail
communication [
          <xref ref-type="bibr" rid="ref14 ref2 ref21">2, 14, 21</xref>
          ] and software engineering repositories, e.g. systems for managing
tasks [
          <xref ref-type="bibr" rid="ref8">8</xref>
          ] and issues [
          <xref ref-type="bibr" rid="ref20">20</xref>
          ]. This information can be used to address information overload
and enhance communication by suggesting relevant information points, e.g. people.
        </p>
        <p>
          Yoo et al. propose a technique for automatically prioritising e-mails by user-specific
priorities derived from personal social networks [
          <xref ref-type="bibr" rid="ref21">21</xref>
          ]. Their technique is designed to
enable training of the algorithms per individual rather than for a whole organisation,
thereby addressing privacy issues. Networks are constructed by clustering nodes, e.g.
according to recipient lists. Importance of contacts is derived from centrality measures.
        </p>
        <p>
          Wolf et al. derive task-based communication between engineers from project
artefacts such as source-code changes, and issue reports [
          <xref ref-type="bibr" rid="ref20">20</xref>
          ]. Their tools and methodology
for constructing social networks have been applied in an industrial project environment
and used for predicting software build failures based on communication patterns.
        </p>
        <p>
          When individuals belong to multiple social networks these can be analysed using
multi-layer social network techniques. For example, Magnani and Rossi propose a
model and an extension to standard measurements for analysing such networks [
          <xref ref-type="bibr" rid="ref17">17</xref>
          ].
        </p>
        <p>Discussion. The techniques for constructing social networks from repositories could
be used to identify people working on related tasks, information hubs etc., which is
relevant for our research. We plan to extend on existing work by automatically deriving
recommendations. Concerning personal integrity, Yoo’s work on personal network data
is promising due to addressing this by limiting data mining to individual users.
2.3</p>
      </sec>
      <sec id="sec-2-3">
        <title>Deriving Useful Connections with Machine Learning Techniques</title>
        <p>
          Borg proposes using machine learning and information retrieval techniques for
supporting engineers in navigating the large and volatile information landscape of software
development projects [
          <xref ref-type="bibr" rid="ref6">6</xref>
          ]. In particular, Borg has applied these techniques to support
automated allocation of issue reports and to provide recommendation support for
impact analysis. New issue reports have been allocated to development teams by training
multiple classifiers on the textual content of previous issue reports and then combining
these when analysing new (incoming) issues. Similar prediction accuracies as for the
manual allocation were obtained, thus saving time in performing this task while
retaining the same quality level of the outcome. For change impact analysis, Borg uses
traditional information retrieval techniques to locate textually similar issue reports. These
are then used as input to identify a set of artefact linked to these (related) issue reports.
These artefacts are weighted using measurements of textual similarity, relative distance
and centrality in the derived network of artefacts, thereby providing a ranked list of
artefacts according to probably of being impacted by the new change. Initial evaluations
show that the algorithms predict 30-40% of previously reported impact when
considering 5-10 of the first recommendations and that the approach could motivate and support
engineers in performing and in validating change impact analyses.
        </p>
        <p>
          Erman et al. apply similar techniques for identifying related test failures when
analysing large amounts of test results from automatic test cases in a multi-branch project
environment [
          <xref ref-type="bibr" rid="ref11">11</xref>
          ]. In this work, test case name, error message and test environment
context were weighted and failed test executions were clustered based on cosine
similarity in the vector space model [
          <xref ref-type="bibr" rid="ref19">19</xref>
          ] using these three components. The technique is
now used in production at the case company for which it was developed. Examples of
supported scenarios include cross-referencing failures across branches and assessing if
a problem is global or local, i.e. isolated to one branch.
        </p>
        <p>Discussion. In our context of enhancing communication, we could apply these
approaches and use machine-learning and information-retrieval techniques for locating
related entities. By identifying related issues or tasks, potentially useful contacts can be
found that may have information that could facilitate the current work. In addition,
identifying other potentially relevant artefacts could provide pointers to additional
repositories to mine. Furthermore, Borg’s clustering techniques may be relevant to apply,
since our case company also performs extensive automatic testing in a multiple branch
environment. By clustering related test failures the teams, projects or individuals
responsible for the connected branches may be relevant contacts.
3</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>Solution Proposal</title>
      <p>
        The proposal will be investigated through a design-science approach [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ] by iteratively
constructing a prototype and evaluating it through case studies at a development
company. The initial focus is to improve coordination from the testers’ perspective.
      </p>
      <p>The developed system will consist of a server and an application that runs on the
users’ mobile phones. The server will interface a number of project repositories for test
cases, issues etc. and connect users’ devices with their user ids for these repositories
using Proximates (see Section 2.1). Social networks will be constructed from
information mined from the project repositories using similar techniques as are described in
Section 2.2. These multi-layer networks will contain information on both existing
entities and connections, and potential connections identified using machine learning and
information retrieval techniques similar to those in Section 2.3. In addition, the physical
encounters, as tracked by Bluetooth, will be represented in an additional network layer.</p>
      <p>Beneficial interactions and topics relevant to two or more proximate users will be
derived based on link predictions in the constructed social graph and on the principle
of triadic closure in sociology. These will then be suggested via the end-user
application. For example, when registered users are noted as being physically close, the social
network will be queried to identify if these users have related topics that could be
discussed, if so an interaction is recommended. Similarly, if a user at a project meeting
requests suitable topics, the social network is filtered for the identified participants and
relevant topics are ranked and presented.</p>
      <p>Key coordinators can be identified from social graphs by centrality analysis. For
example, betweeness centrality can identify members critical to the information transfer
and links or nodes that need to be reinforced through redundancy. Furthermore,
eigencentrality can be used to identify influential key members. This information can
help management in adjusting office seating and organisational structures.</p>
      <p>In addition to providing useful functionality to the users, the system will track their
physical interactions including identified meetings. The users’ responses to interaction
recommendations will also be tracked in order to train the system and to evaluate the
underlying algorithms used to derive recommendations.</p>
      <p>The prototype will be designed and evaluated for a development team at a large
development company. This team consists of product owner, developers, testers, project
managers etc., and interacts with other development teams and testing units both
onand off-site. The impact on requirements communication and its effect on project
coordination, e.g. lead times and software quality, will be evaluated. The research will also
consider the ethical and legal aspects of tracking and using information connected to
individuals and their privacy, e.g. in selecting and displaying information, and in
storing it. This is also an important aspect in securing participants for the evaluation.
4</p>
    </sec>
    <sec id="sec-4">
      <title>Summary and Future Plan</title>
      <p>We propose improving project coordination by providing recommendations for what to
discuss with project members who are physically close. These recommendations will
be based on information mined from project repositories using a combination of
techniques from social network analysis and machine learning. In addition to enhancing
communication and collaboration between engineers this research will provide a
platform for studying team interactions.</p>
      <p>We plan to investigate and evaluate these ideas in close collaboration with an
industrial partner with a focus on improving requirements communication towards test
engineers. A prototype will be iteratively developed and evaluated through use in a
development project. Apart from evaluating the impact on requirements-test coordination,
the research is expected to yield new insights and contributions into how team members
in general and test engineers in particular interact and collaborate, and how to improve
development processes in order to enhance project coordination.</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          1.
          <string-name>
            <surname>Allen</surname>
            <given-names>T.</given-names>
          </string-name>
          <article-title>Managing the Flow of Technology</article-title>
          . Cambridge, MA, MIT Press,
          <year>1977</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          2.
          <string-name>
            <surname>Bird</surname>
            <given-names>C</given-names>
          </string-name>
          , et al.
          <article-title>Mining email social networks</article-title>
          .
          <source>Proceedings of the 2006 International Workshop on Mining Software Repositories. ACM</source>
          ,
          <year>2006</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          3.
          <string-name>
            <surname>Bjarnason</surname>
            <given-names>E</given-names>
          </string-name>
          , et al.
          <article-title>Challenges and Practices in Aligning Requirements with Verification and Validation: a Case Study of Six Companies</article-title>
          .
          <source>Empirical Softw Engin</source>
          .
          <volume>19</volume>
          .6:
          <fpage>1809</fpage>
          -
          <lpage>1855</lpage>
          ,
          <year>2014</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          4.
          <string-name>
            <surname>Bjarnason</surname>
            <given-names>E</given-names>
          </string-name>
          ,
          <string-name>
            <surname>Sharp</surname>
            <given-names>H</given-names>
          </string-name>
          .
          <article-title>The Role of Distances in Requirements Communication: a Case Study</article-title>
          .
          <source>Requirements Engineering</source>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>26</lpage>
          ,
          <year>2015</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          5.
          <string-name>
            <surname>Bjarnason</surname>
            <given-names>E</given-names>
          </string-name>
          et al.
          <source>A Theory of Distances in Software Engineering. Inf &amp; Softw Tech</source>
          ,
          <year>2015</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          6.
          <string-name>
            <surname>Borg</surname>
            <given-names>M.</given-names>
          </string-name>
          <article-title>Embrace your Issues: Compassing the Software Engineering Landscape using Bug Reports</article-title>
          .
          <source>Proc.of 29th ACM/IEEE Int.Conf. on Automated Softw. Engin</source>
          .
          <year>2014</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          7.
          <string-name>
            <surname>Corral</surname>
            <given-names>L</given-names>
          </string-name>
          et al.
          <article-title>DroidSense: a Mobile Tool to Analyze Software Development Processes by Measuring Team Proximity</article-title>
          . Objects, Models, Comp.,
          <source>Patterns</source>
          . Springer, pp.
          <fpage>17</fpage>
          -
          <lpage>33</lpage>
          ,
          <year>2012</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          8.
          <string-name>
            <surname>Damian</surname>
            <given-names>D</given-names>
          </string-name>
          et al.
          <article-title>The Role of Domain Knowledge and Cross-Functional Communication in Socio-Technical Coordination</article-title>
          .
          <source>IEEE ICSE</source>
          <year>2013</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          9.
          <string-name>
            <surname>Eagle</surname>
            <given-names>N</given-names>
          </string-name>
          ,
          <string-name>
            <surname>Pentland</surname>
            <given-names>AS</given-names>
          </string-name>
          .
          <article-title>Social Serendipity : Proximity Sensing and Cueing</article-title>
          .
          <source>MIT Technical report</source>
          .
          <year>2004</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          10.
          <string-name>
            <surname>Eppler</surname>
            <given-names>MJ</given-names>
          </string-name>
          ,
          <string-name>
            <surname>Mengis</surname>
            <given-names>J</given-names>
          </string-name>
          <article-title>The Concept of Information Overload: A Review of Literature from Organization Science</article-title>
          , Accounting, Marketing,
          <string-name>
            <surname>MIS</surname>
          </string-name>
          , and
          <string-name>
            <given-names>Related</given-names>
            <surname>Disciplines</surname>
          </string-name>
          .
          <source>The Information Society 20.5</source>
          ,pp.
          <fpage>325</fpage>
          -
          <lpage>344</lpage>
          ,
          <year>2004</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          11.
          <string-name>
            <surname>Erman</surname>
            <given-names>N</given-names>
          </string-name>
          et al.
          <article-title>Navigating Information Overload Caused by Automated Testing - a Clustering Approach in Multi-Branch Development</article-title>
          ,
          <source>IEEE 8th Int. Conf on Software Testing, Verification and Validation</source>
          (ICST) pp.
          <fpage>1</fpage>
          -
          <issue>9</issue>
          ,
          <fpage>13</fpage>
          -
          <lpage>17</lpage>
          , April 2015
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          12.
          <string-name>
            <surname>Jonsson</surname>
            <given-names>H</given-names>
          </string-name>
          ,
          <string-name>
            <surname>Nugues P Proximates-A Social Context</surname>
          </string-name>
          <article-title>Engine</article-title>
          .
          <source>Evolving Ambient Intelligence</source>
          . Springer International Publishing, pp.
          <fpage>230</fpage>
          -
          <lpage>239</lpage>
          ,
          <year>2013</year>
          ,
        </mixed-citation>
      </ref>
      <ref id="ref13">
        <mixed-citation>
          13.
          <string-name>
            <surname>Jonsson</surname>
            <given-names>H</given-names>
          </string-name>
          et al.
          <article-title>Proximity-Based Reminders using Bluetooth</article-title>
          ,
          <source>IEEE Int Conf on Pervasive Comp and Comm Worksh (PERCOMW)</source>
          , pp.
          <fpage>151</fpage>
          -
          <lpage>153</lpage>
          ,
          <year>2014</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref14">
        <mixed-citation>
          14.
          <string-name>
            <surname>Gomes</surname>
            <given-names>LH</given-names>
          </string-name>
          , et al.
          <source>Improving Spam Detection Based on Structural Similarity. SRUTI 5</source>
          ,
          <year>2005</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref15">
        <mixed-citation>
          15.
          <string-name>
            <surname>Hevner</surname>
            <given-names>AR</given-names>
          </string-name>
          et al.
          <source>Design Science in Information Systems Research. MIS Q. 0276-7783</source>
          , vol
          <volume>28</volume>
          , issue 1, pp.
          <fpage>75</fpage>
          -
          <lpage>105</lpage>
          ,
          <year>2004</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref16">
        <mixed-citation>
          16.
          <string-name>
            <surname>Karr-Wisniewski</surname>
            <given-names>P</given-names>
          </string-name>
          ,
          <string-name>
            <surname>Lu</surname>
            <given-names>Y.</given-names>
          </string-name>
          <string-name>
            <surname>When</surname>
          </string-name>
          <article-title>More is Too Much: Operationalizing Technology Overload</article-title>
          and
          <article-title>Exploring its Impact on Knowledge Worker Productivity</article-title>
          .
          <source>Computers in Human Behavior 26.5</source>
          , pp.
          <fpage>1061</fpage>
          -
          <lpage>1072</lpage>
          ,
          <year>2010</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref17">
        <mixed-citation>
          17.
          <string-name>
            <surname>Magnani</surname>
            <given-names>M</given-names>
          </string-name>
          ,
          <article-title>Rossi L The ML-Model for Multi-Layer Social Networks</article-title>
          .
          <source>Advances in Social Networks Analysis and Mining (ASONAM)</source>
          ,
          <source>2011 Int Conf on. IEEE</source>
          ,
          <year>2011</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref18">
        <mixed-citation>
          18.
          <string-name>
            <surname>Nguyen</surname>
            <given-names>T</given-names>
          </string-name>
          et al.
          <source>Global Software Development and Delay: Does Distance Still Matter?. IEEE Int Conf on Global Softw Eng (ICGSE</source>
          <year>2008</year>
          ),
          <year>2008</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref19">
        <mixed-citation>
          19.
          <string-name>
            <surname>Salton</surname>
            <given-names>G</given-names>
          </string-name>
          et al.
          <article-title>A Vector Space Model for Automatic Indexing</article-title>
          .
          <source>Communications of the ACM 18.11</source>
          (
          <year>1975</year>
          ):
          <fpage>613</fpage>
          -
          <lpage>620</lpage>
          ,
          <year>1975</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref20">
        <mixed-citation>
          20.
          <string-name>
            <surname>Wolf</surname>
            <given-names>T</given-names>
          </string-name>
          et al.
          <article-title>Mining Task-Based Social Networks to Explore Collaboration in Software Teams</article-title>
          .
          <source>IEEE Software</source>
          ,
          <volume>26</volume>
          .1, pp.
          <fpage>58</fpage>
          -
          <lpage>66</lpage>
          ,
          <year>2009</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref21">
        <mixed-citation>
          21.
          <string-name>
            <surname>Yoo</surname>
            <given-names>S</given-names>
          </string-name>
          et al.
          <article-title>Mining Social Networks for Personalized Email Prioritization</article-title>
          .
          <source>Proc 15th ACM SIGKDD Int Conf on Knowledge discovery and data mining</source>
          .
          <year>2009</year>
          .
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>