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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Optimized advertising content delivery in affiliate networks</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Daniel Mican</string-name>
          <email>daniel.mican@econ.ubbcluj.ro</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Business Information Systems Department Babe s</institution>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Daniel Mican is 2nd year PhD student in Business Information Systems at Babes.-Bolyai University of Cluj-Napoca</institution>
          ,
          <addr-line>Romania and his advisor is Prof. Dr. Nicolae Tomai, nico-</addr-line>
        </aff>
      </contrib-group>
      <abstract>
        <p>This study tackles the problem of advertising content distribution in a liate networks. We model the a liate network as a new business-to-business relationship in which a master site tries to improve its pro ts by properly targeting the advertising information. In our speci c case, we will optimize discount coupons delivery for one of the biggest coupons site in the world. In our study we will employ adapted recommendation strategies based on collaborative ltering methods. The purpose of the present paper is to correlate the display of advertising information on a liate sites with the actual improvements in sales, as a direct method to obtain the user rating which does not exist.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;recommender systems</kwd>
        <kwd>collaborative ltering</kwd>
        <kwd>a liates</kwd>
        <kwd>content delivery</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. INTRODUCTION</title>
      <p>This paper describes the research proposal we are working
at and which is part of my PhD thesis. It speci cally targets
electronic business by tackling a new and emerging
businessto-business relationship. In electronic B2B, a provider has
various means of attracting new customers, one of them
being to supply and promote discount coupons. A proper
platform for spreading out advertising information regarding
discounts is required, and the information providers should
possess intelligent tools to observe and evaluate the e ciency
of the discounts information distribution. A liate programs
represent possible solution to be adopted. In e-commerce,
an a liate is a website which links back to an e-commerce
site like Amazon.com. While in classical e-commerce, the
provider can easily compute the e ciency and the e
ectiveness of a particular a liate, because it can register all
products sold through that a liate, in discount information
advertising this operation is no longer possible. In discount
advertising, the customer usually buys the product directly
from the provider e-commerce platform and the provider has
no mean to directly identify how the customer acquired the
information about the discount. Thus, classical tools for
personalized content delivery can not be directly applied for
optimizing the advertising delivery information, due to the
fact that the direct feedback loop is missing.</p>
      <p>In this paper we will give a brief description of the research
problem stressed in the paragraph above, stating out the
challenges we are facing. The paper is organized as follows.
Section 2 presents the research problem of my PhD thesis. In
section 3 we present the state of the art, mainly concerning
the intelligent techniques for content delivery and studies
concerning the a liates problem. Section 4 describes the
main challenges we face in our study, while section 5 presents
the wow-coupons.com use case. We conclude the paper by
presenting our future plans.</p>
    </sec>
    <sec id="sec-2">
      <title>2. RESEARCH PROBLEM</title>
      <p>Our main research problem is to build an e-business
system in the area of a liates marketing and content delivery.
Speci cally, we try to develop a delivery system for a
major coupons site. Coupons represent a well-established way
of providing bene ts to customers for a speci c activity to
improve their business.</p>
      <p>Online coupons or online coupon codes are discounts and
bargain deals for all major on line stores and shopping sites
on the Internet. Online stores creates discount codes to
select groups of customers. By using coupon codes some
groups of people will enjoy discounts when shopping online,
like free shipping. Discount coupons is a way to save with on
line shopping and some codes will be automatically applied
at checkout. Other codes must be copy pasted intro a special
coupon text box before to con rm the order.</p>
      <p>
        An independent research agency made a recent survey on
behalf of Pay By Touch on over 100 shoppers that were
questioned in May 2007. The survey proves [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] that
shoppers develop a positive response to discount schemes if these
are both highly targeted and convenient to use. In fact,
the survey reveals that 88% of shoppers would use discount
coupons, if these were more focused on their product
preferences and were available in store while they were shopping.
Of those surveyed, 95% of shoppers who used a retail loyalty
card have received in-store discount coupons. However, 75%
of these shoppers said they frequently forget to redeem them
even if some of the discounts o ered were on items they
normally buy. Other factors that contributed to low redemption
rates were the inconvenience of having to carry pieces of
paper around and the fact that discounts were mostly for items
the shopper did not have a history of buying. Therefore, it
seems clear that retailers who o er targeted discounts and
make it easy for those o ers to be redeemed, could have
a compelling way to develop customer loyalty and increase
pro t.
      </p>
      <p>In our study case we want to speci cally develop and
implement a content delivery system for one of the top coupons
site in USA (http://wow-coupons.com/). From now on, we
will name this site as the master site. Our system will search,
select and deliver coupons on behalf of 3'rd party sites that
sell or recommend products, or for community sites that
offer valuable user targeted content. Delivery will be targeted
to a network of a liates, established in order to enhance
information dissemination. Delivered content will assist the
site visitors, the community members in their online
shopping activities and will help them to save money when they
buy products. Our main target is to optimize the system
such us to deliver highly targeted discount coupons. For
our target, we intend to adapt recommendation systems and
collaborative ltering technologies. Another feature of our
interest is to technically enable the coupons site to deliver
the content in real-time, i.e. without the usage of o -line
information exchange with the a liates. When a new coupon
is added on the master site, the content delivered on the
a liate sites should be seamless updated.</p>
      <p>
        Collaborative ltering is of our interest because it is a way
to establish what items to display to web users who have
browsed some ads or made purchases in the past.
Collaborative ltering software compiles purchasing information on
customers to pool them into clusters and uses some cluster
members' purchasing patterns to predict the buying habits
of others in the same cluster. It does this in real time and,
for instance, puts an ad on the customer's screen while he
or she is making a purchase [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. In our case we want to
display targeted discount coupons to users that are going to
make a purchase. For example, we target an online
shopping website that makes discount recommendations for the
products the customer has in her shopping chart. This will
help her to save money and also to develop a strong loyalty
for that online shop because it proves that the shop cares
about the customers and their needs.
      </p>
      <p>To directly apply collaborative ltering, we need to collect
and represent di erent partner sites and people preferences.
Preferences are typically based on item ratings (i.e.
posteriori feedback) explicitly delivered by users. The system
recommends products which were evaluated positively by
another similar user or by a set of such users.</p>
      <p>Our main challenge is that we cannot collect the user
ratings or preferences because we deliver the advertising
content (coupon codes). The coupon code for a particular
product and promotion campaign is the same, regardless the site
that publishes it. When a user applies a coupon by buying
a product, we do not have a direct method to identify the
a liate site that published the coupon to the user.
Therefore, in our business setup, we do not have the feedback
loop mechanism to allow us to use a classical collaborative
ltering method.</p>
      <p>Instead, we want to implement a module part of the master
site system that will allow it build a pro le for each a
liate. This module will track down and monitor how many
times an a liate user viewed and clicked on every coupon
displayed. On the other side, the master knows the number
of products sold per every coupon delivered to all a liates.
All these will aggregate in a statistical information that will
replace the classical feedback from the partners and will
provide the a liate pro le. The master can optimize and
improve the coupons delivery algorithm for the entire a liates
network.</p>
      <p>In this section we described our research problem in the
terms of our B2B relationships. But, the problem is more
general, spanning over all business relationships where
direct feedback or user rating is not available. By tackling the
a liates problem, we intend to prove that intelligent
techniques for content information delivery are more suited and
can enhance the pro t of the advertisers, even if there are
only statistical glues about the real pro le of the information
users.</p>
    </sec>
    <sec id="sec-3">
      <title>3. STATE OF THE ART IN THE FIELD</title>
      <p>In this section we will investigate the state of the art in
the elds covered by our research. We should emphasize
that there is a lot of bibliography tackling recommender
systems and collaborative ltering. Regarding the a liates,
there are a lot of business studies concerning the a liates
in e-commerce setups. In e-commerce setups, the feedback
loop is closed because the master can identify through which
channel a speci c purchase was performed. Therefore,
besides a proper advertising, one of their biggest challenge is
how to compensate or reward each a liate, accordingly to
the pro ts they generated. In our study we are not
interested in designing a proper reward scheme for a liates, we
suppose that we have good mechanisms to maintain the
network and make it growing.</p>
    </sec>
    <sec id="sec-4">
      <title>3.1 Recommender systems and collaborative filtering</title>
      <p>
        Recommender systems are an important part of recent
ecommerce. They enable the increase of sales by suggesting
to users selected products on o er. The problem of how to
choose the most suitable items, possibly with respect to the
user's inclinations, is a challenging research problem that
has been investigated for many years [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. The purpose of a
recommender system is to eliminate the need for browsing
the entire item space by presenting the user with items of
interest early on. Recommender systems strive to
recommend items that users will appreciate and rate highly, often
presenting items in order of highest predicted ratings rst
[
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. The most well-known example of collaborative ltering
is Amazon. The purchase recommendations are based on
the following rule: "users who are interested in item X are
also likely to be interested in item Y".
      </p>
      <p>
        Four fundamental approaches to recommendation can be
mentioned: demographic ltering, collaborative and
contentbased recommendation, and simpli ed statistical approaches
[
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. We will describe them according to [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ].
      </p>
      <p>In demographic recommendation, users are classi ed based
on their personal data, which was collected during the
registration process, survey responses or other feedback methods.
Each product is assigned to one or more classes with certain
weights and the user is attracted to items from the class
closest to their pro le. This is attribute based
recommendation.</p>
      <p>Collaborative recommendation is typically based on item
ratings explicitly delivered by users. The system recommends
products, which have been evaluated positively by another
similar user or by a set of such users, whose ratings have the
strongest correlation with the current user. This is
user-touser correlation.</p>
      <p>Content-based recommendation focuses on the similarity
between products, usually taking into account their features
like textual descriptions, hyperlinks, related ratings, or
cooccurrence in the same purchased transactions or web user
sessions. Items that are the closest to the most recently
processed (viewed), are recommended regardless of user
preferences. This is item-to-item correlation. Association rules
and sequential patterns are the most interesting techniques
used in recommendation based on item-to-item correlation.
They are usually applied to data sets related to items such as
purchases, ratings of TV programs, navigation paths rather
than directly to item attributes.</p>
      <p>
        In the statistical approach, the user is shown products based
on some statistical factors; usually popularity measures like
averages or summary ratings (the best rated), and numbers
of sold units (the best buy) [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ].
      </p>
      <p>
        The information overload problem a ects our everyday
experience while searching for knowledge on a topic. To
overcome this problem, we often rely on suggestions from others
who have more experience on the topic. However, in web
case where there are numerous suggestions, it is not easy to
detect the trustworthy ones. Shifting from individual to
collective suggestions, the process of recommendation becomes
controllable. This is attained with the introduction of
Collaborative Filtering (CF), which provides recommendations
based on the suggestions of users who have similar
preferences. Since CF is able to capture the particular preferences
of a user, it has become one of the most popular methods in
recommender systems [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
      </p>
      <p>
        A web site or other online service that receives extensive
tra c has the potential to analyze the resulting usage data
for the bene t of its user population. One of the most
common applications of such analysis is collaborative ltering.
A web site o ering items for sale or download can analyze
the aggregate decisions of the whole population, and then
make recommendations to individual users of further items
that they are likely to be interested in. The
recommendations made to a speci c user are thus based not just on his
or her own previous actions, but also on collaborative
information, the information collected from other users in the
system [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
      </p>
      <p>
        Collaborative ltering algorithms can be categorized as [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ]:
User-Based algorithms: operate on the assumption that
consumers who have bought similar products in the
past will prefer to buy similar products in the future
Item-Based algorithms: operate on the assumption
that items that have been co-purchased in the past
will continue to be co-purchased in the future
Regarding the technical mean of delivering the
recommendations, CF are split in [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]:
memory-based algorithms, which recommend
according to the preferences of nearest neighbors. They
utilize the entire user-item database to generate a
prediction. These systems employ statistical techniques
to nd a set of users, known as neighbors, that have
a history of agreeing with the target user (i.e., they
either rate di erent items similarly or they tend to
buy similar set of items). Once a neighborhood of
users is formed, these systems use di erent algorithms
to combine the preferences of neighbors to produce
a prediction or top-N recommendation for the active
user. The techniques, also known as nearest-neighbor
or user-based collaborative ltering are more popular
and widely used in practice.
model-based algorithms, which recommend by rst
developing a model of user ratings. Algorithms in this
category take a probabilistic approach and envision
the collaborative ltering process as computing the
expected value of a user prediction, given his/her ratings
on other items. The model building process is
performed by di erent machine learning algorithms such
as Bayesian network, clustering, and rule-based
approaches. The Bayesian network model formulates
a probabilistic model for collaborative ltering
problem. Clustering model treats collaborative ltering as
a classi cation problem and works by clustering
similar users in same class and estimating the
probability that a particular user is in a particular class C,
and from there computes the conditional probability
of ratings. The rule-based approach applies
association rule discovery algorithms to nd association
between co-purchased items and then generates item
recommendation based on the strength of the association
between items.
      </p>
      <p>
        Both practical experience and related research have reported
that memory-based algorithms present excellent performance,
in terms of accuracy, for multivalue rating data. On the
other hand, model-based algorithms are e ciently handle
scalability to large data sets [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ].
      </p>
    </sec>
    <sec id="sec-5">
      <title>3.2 Affiliates marketing</title>
      <p>A liate marketing is a web-based marketing practice in
which a business rewards one or more a liates for each
visitor or customer brought about by the a liate's marketing
e orts. A merchant, also known as an advertiser or retailer,
is a web site or company that sells a product or service
online, accepts payments and ful lls orders. A liates (also
called publishers) place merchants' ads, text links, or
product links on their web sites, shopping engines, blogs, etc.
or include them in e-mail campaigns and search listings in
exchange for commissions on leads or sales.</p>
    </sec>
    <sec id="sec-6">
      <title>4. MAIN CONTRIBUTIONS EXPECTED</title>
      <p>We expect to contribute in several main areas.</p>
      <p>From the systemic point of view, we intend to de ne the
overall picture comprising all business to business
relationships. Figure 1 presents an overall sketch of our system.
Our contribution will mainly reside in the WOW-Coupons.com
master site where we will technically embed a recommender
system.</p>
      <p>From a systemic point of view, we intend to de ne the overall
picture comprising all business to business relationships.
Our contribution will mainly reside in the WOW-Coupons.com
master site where we will technically embed a recommender
system.</p>
      <p>
        From a technical point of view, a challenge is how to pack
the content delivered to a liate sites so as the partners will
seamlessly accept the content and publish it into their
websites. The content should be delivered in such a way that
we will be able to register the number of views per coupon
and number of clicks per coupon. We envisage the usage of
server-controlled web development techniques that exchange
small amount of information behind the scene. AJAX
technologies [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] are a good candidate for our reason. We intend
to fully describe our solution from the technical point of
view.
      </p>
      <p>From a algorithmic point of view, our research raises several
open issues:
to develop a statistical analysis tool in order to relate
in a signi cant manner the collected information about
content display (number of views and clicks) and the
received payments from the earning reports.
Statistical analysis will provide a way to collect the required
feedback in the collaborative ltering methods
to select a proper user pro le management scheme.
This is highly related with adapting a recommendation
system or collaborative ltering method to our setup.
Up to now, we only investigated several alternatives,
but we did not established which algorithm would be
more suited for us. We expect the ICEC doctoral
symposium to allow us to progress on this issue, by having
discussions with highly esteemed experts
to compare the intelligent content distribution to the
actual functioning of the a liates system. Actually,
there is not too much intelligence in the system, in the
sense that the master delivers to each site the coupons
related with the latest marketing campaign added in
the master's database. In order to allow for a
nonbiased comparison, we need to design a controlled
experiment on wow-coupons.com, covering a de ned
period of time and a stable part of the a liates network.
Designing and running the experiments are a big
challenge, because, in meantime, we need not to downward
the business performance over the period of the
experiment.</p>
    </sec>
    <sec id="sec-7">
      <title>5. WOW-COUPONS.COM</title>
      <p>
        We started this research because we intend to improve the
way that WOW-Coupons.com delivers the coupons for the
a liate sites. The actual system delivers the last coupons
added on the master site, organized by store and by category.
Up to now, this delivery scheme proved to be winning, but
in nowadays this module needs some improvements because
we intend to enhance the user usage of time and also the
pro ts wow-coupons.com makes from the a liates network.
We will try to do a brief description of the site that will use
the recommender system that we want to provide below.
The overwhelming majority of consumers in the US collect
coupons to help them make the most of their money.
Consumers spend plenty during the holiday season, and with
tightening budgets, they are spending money where they see
the best deals. During the holidays, an impressive 71% of
survey respondents [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] say they're likely to use the Internet
to research and compare holiday products and gifts.
WOW-Coupons.com is the fastest-growing coupons site on
the web. It is a winner of 2005 LinkShare Gold Link
"Innovative A liate" award. Averaging around 600,000 unique
visitors a month and with a steadily growing community of
e-mail newsletter subscribers, currently more than 80,000,
it commands positions at the top of the search engines.
A few time ago the company launched the UK version of
the site WOW-Coupons.co.uk. Categories include printable
vouchers with Printable Retail, Printable Grocery, Printable
Restaurant and Printable Travel Coupons subcategories, as
well as Online Coupons.
      </p>
      <p>Printable retail coupons section will provide real coupons
buyers can take to favorite major retailers and national
franchise stores. Shoppers choose the discount, print it out, and
go shopping without needing to sign up. The process
eliminates clogged inboxes with endless promotional e-mails from
dozens of mailing lists. Grocery printable vouchers section
will provide the grocery coupons users need, when they need
them. Print coupons to save on favorite brands at
supermarkets and drugstores everywhere. Restaurant printable
vouchers section will provide coupons that can be printed
out and used to save money at restaurants across the
nation. When eating out may seem like an extravagance, think
again and enjoy dinner. Travel and entertainment printable
vouchers section will provide discounts and vouchers for
diverse traveling destinations whether in US, U.K. or
internationally. Travelers can still a ord to take vacations or visit
the family. The site has printable travel coupons and o ers
for car rentals, accommodations, amusement parks,
museums and lots more.</p>
      <p>Just like printable vouchers, the best and biggest retailers
and service providers o er online coupons and special
discounts. The di erence is, these can be used only for
purchases made online. On the site visitors can browse great
o ers, go straight to a favorite store (arranged
alphabetically or by date posted) to see the latest deals, or to use the
navigation menu on the right side of the site. When an item
is found, the user can follow directions in the description
of each coupon to be sure that savings have been applied
before paying for an order.</p>
      <p>
        For implementing the architectural design for coupons
delivery, we employed the XML standard to provide an RSS
[
        <xref ref-type="bibr" rid="ref6">6</xref>
        ] service. Wow-coupons.com has many sites that download
the RSS and display the content that we deliver. For some
a liate sites we created a special customized RSS feed.
Every coupon is part of a category and has a simple XML
format. Now the system generates around 1500 di erent XML
les that can be used on the Internet. The system generates
an XML le and update it hourly for every company that
have coupons in the database.
      </p>
    </sec>
    <sec id="sec-8">
      <title>6. FUTURE PLANS</title>
      <p>Our future plans intend to cover the above mentioned issues.
We are only in the incipient stage of our research, because
I have spent all the rst year in taking exams and now,
we worked on de ning a proper problem and researching
various technologies for this problem. Up to now,
Wowcoupons got implemented without the optimization feature
and to perform the optimization mentioned in this paper is a
good plan for future research. We also think that this study
will represent a good opportunity to advertise to the a liate
marketing community the potential of intelligent techniques.</p>
    </sec>
    <sec id="sec-9">
      <title>7. ACKNOWLEDGMENTS</title>
      <p>This work is supported by the Romanian Authority for
Scienti c Research under project IDEI 573. We also
acknowledge the support from Mrs. Elena Potoupa, CEO of WOW
Things Inc., owner of wow-coupons.com.</p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          [1]
          <string-name>
            <given-names>J. J.</given-names>
            <surname>Garrett</surname>
          </string-name>
          .
          <article-title>Ajax: A new approach to web applications</article-title>
          .
          <source>Adaptive Path, 18 February</source>
          <year>2005</year>
          . http://www.adaptivepath.com/ideas/essays/archives/000385.ph
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          [2]
          <string-name>
            <given-names>P.</given-names>
            <surname>Kazienko</surname>
          </string-name>
          and
          <string-name>
            <given-names>M.</given-names>
            <surname>Kiewra</surname>
          </string-name>
          .
          <article-title>Personalized recommendation of web pages</article-title>
          . In T. Nguyen, editor,
          <source>Intelligent Technologies for Inconsistent Knowledge Processing</source>
          , pages
          <volume>163</volume>
          {
          <fpage>183</fpage>
          . Advanced Knowledge International, Adelaide, Australia,
          <year>2004</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          [3]
          <string-name>
            <given-names>P.</given-names>
            <surname>Kazienko</surname>
          </string-name>
          and
          <string-name>
            <given-names>P.</given-names>
            <surname>Kolodziejski</surname>
          </string-name>
          .
          <article-title>Personalized integration of recommendation methods for e-commerce</article-title>
          .
          <source>International Journal of Computer Science and Applications</source>
          ,
          <volume>3</volume>
          (
          <issue>3</issue>
          ):
          <volume>12</volume>
          {
          <fpage>26</fpage>
          ,
          <year>2006</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          [4]
          <string-name>
            <given-names>J.</given-names>
            <surname>Kleinberg</surname>
          </string-name>
          and
          <string-name>
            <given-names>M.</given-names>
            <surname>Sandler</surname>
          </string-name>
          .
          <article-title>Using mixture models for collaborative ltering</article-title>
          .
          <source>J. Comput. Syst. Sci.</source>
          ,
          <volume>74</volume>
          (
          <issue>1</issue>
          ):
          <volume>49</volume>
          {
          <fpage>69</fpage>
          ,
          <year>2008</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          [5]
          <string-name>
            <given-names>T.</given-names>
            <surname>Nathanson</surname>
          </string-name>
          , E. Bitton, and
          <string-name>
            <given-names>K.</given-names>
            <surname>Goldberg</surname>
          </string-name>
          .
          <article-title>Eigentaste 5.0: constant-time adaptability in a recommender system using item clustering</article-title>
          .
          <source>In RecSys '07: Proceedings of the 2007 ACM conference on Recommender systems</source>
          , pages
          <volume>149</volume>
          {
          <fpage>152</fpage>
          , New York, NY, USA,
          <year>2007</year>
          . ACM.
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          [6]
          <string-name>
            <given-names>M.</given-names>
            <surname>Pilgrim</surname>
          </string-name>
          .
          <article-title>What is rss? XML.com, 18 December 2002</article-title>
          . http://www.xml.com/pub/a/2002/12/18/diveinto-xml.html.
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          [7]
          <string-name>
            <given-names>J.</given-names>
            <surname>Riedl</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J.</given-names>
            <surname>Konstan</surname>
          </string-name>
          , and
          <string-name>
            <given-names>E.</given-names>
            <surname>Vrooman</surname>
          </string-name>
          .
          <article-title>Word of Mouse: The Marketing Power of Collaborative Filtering</article-title>
          .
          <source>Business Plus</source>
          ,
          <year>2002</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          [8]
          <string-name>
            <given-names>B.</given-names>
            <surname>Sarwar</surname>
          </string-name>
          , G. Karypis,
          <string-name>
            <given-names>J.</given-names>
            <surname>Konstan</surname>
          </string-name>
          , and
          <string-name>
            <given-names>J.</given-names>
            <surname>Reidl</surname>
          </string-name>
          .
          <article-title>Item-based collaborative ltering recommendation algorithms</article-title>
          .
          <source>In WWW '01: Proceedings of the 10th international conference on World Wide Web</source>
          , pages
          <volume>285</volume>
          {
          <fpage>295</fpage>
          , New York, NY, USA,
          <year>2001</year>
          . ACM.
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          [9]
          <string-name>
            <given-names>J. B.</given-names>
            <surname>Schafer</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J. A.</given-names>
            <surname>Konstan</surname>
          </string-name>
          , and
          <string-name>
            <given-names>J.</given-names>
            <surname>Riedl</surname>
          </string-name>
          .
          <article-title>E-commerce recommendation applications</article-title>
          .
          <source>Data Min. Knowl. Discov.</source>
          ,
          <volume>5</volume>
          (
          <issue>1</issue>
          -2):
          <volume>115</volume>
          {
          <fpage>153</fpage>
          ,
          <year>2001</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          [10]
          <string-name>
            <given-names>M. S.</given-names>
            <surname>Sodhi</surname>
          </string-name>
          .
          <article-title>A match made in heaven</article-title>
          .
          <source>Operations Research Management Science Today</source>
          ,
          <volume>28</volume>
          (
          <issue>1</issue>
          ),
          <year>February 2001</year>
          . http://www.lionhrtpub.com/orms/orms-2- 01/sodhi.html.
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          [11]
          <string-name>
            <given-names>P.</given-names>
            <surname>Symeonidis</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A.</given-names>
            <surname>Nanopoulos</surname>
          </string-name>
          ,
          <string-name>
            <given-names>A. N.</given-names>
            <surname>Papadopoulos</surname>
          </string-name>
          , and
          <string-name>
            <given-names>Y.</given-names>
            <surname>Manolopoulos</surname>
          </string-name>
          .
          <article-title>Collaborative recommender systems: Combining e ectiveness and e ciency</article-title>
          .
          <source>Expert Syst. Appl.</source>
          ,
          <volume>34</volume>
          (
          <issue>4</issue>
          ):
          <volume>2995</volume>
          {
          <fpage>3013</fpage>
          ,
          <year>2008</year>
          .
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          [12]
          <string-name>
            <given-names>S.</given-names>
            <surname>Thompson</surname>
          </string-name>
          .
          <article-title>A question of loyalty</article-title>
          .
          <source>Retail Systems Magazine</source>
          , pages
          <volume>47</volume>
          {
          <fpage>50</fpage>
          ,
          <string-name>
            <surname>August</surname>
            <given-names>-September</given-names>
          </string-name>
          <year>2007</year>
          . http://www.retailsystems.com/pages/past issues/aug sept 07/pdfs/a question of.
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>