Ontologically-Enriched Unified User Modelingfor Cross-System Personalization

Bhaskar Mehta1, Claudia Niederee1, Avare Stewart1,Marco Degemmis2, Pasquale Lops2, and Giovanni Semeraro2

1 Fraunhofer IPSI, Darmstadt 64293, Germany2 Dipartimento di Informatica, Universita di Bari, Bari 70126, Italy

{mehta, stewart, niederee}@ipsi.fraunhofer.de{degemmis, lops, semeraro}@di.uniba.it

Abstract. Personalization today has wide spread use on many Websites. Systems and applications store preferences and information aboutusers in order to provide personalized access. However, these systemsstore user profiles in proprietary formats. Although some of these systemsstore similar information about the user, exchange or reuse of informationis not possible and information is duplicated. Additionally, since userprofiles tend to be deeply buried inside such systems, users have littlecontrol over them. This paper proposes the use of a common ontology-based user context model as a basis for the exchange of user profilesbetween multiple systems and, thus, as a foundation for cross-systempersonalization.1

1 Introduction

Typically, personalization occurs separately within each system that one inter-acts with. Each system independently builds up user profiles, i.e. informationabout a user’s likes/dislikes, and uses this information to personalize the sys-tem’s content and service offer. Most of the personalization techniques [4] relyon either the implicit collection of information about users by tracking andanalyzing their system usage behavior or the users explicitly providing informa-tion about themselves or giving feedback to the system. Such approaches havetwo major drawbacks: 1) investments of users in personalizing a system are nottransferable to other systems; 2) users have little or no control over the informa-tion that defines their profile. Cross system personalization, i.e. personalizationthat shares information across different systems in a user-centric way, can over-come the aforementioned problems. Information about users, which is originallyscattered across multiple systems, is combined to obtain maximum leverage. Inthis paper we present the Unified User Context Model(UUCM), an extensible,ontology based user context model, that is the foundation of the approach tocross-system personalization as an application of unified user models. The userbecomes a hub and a switch, moving, controlling and synchronizing user profiledata as part of a so-called Context Passport [3].

1 This research was partially funded under the IST-2003-507173 Project VIKEF.

L. Ardissono, P. Brna, and A. Mitrovic (Eds.): UM 2005, LNAI 3538, pp. 119–123, 2005.c© Springer-Verlag Berlin Heidelberg 2005

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2 Related Work

User models have been used in recommender systems for content processing andinformation filtering. Recommender systems, by observing preferences throughinteractions with users, keep summaries of their preferences in a user model,and utilize this model to adapt themselves to generate customized informationor behavior. Systems incorporating models of users interest [2] and other cogni-tive patterns have been widely used to selectively filter information on behalf ofusers. Task models of user are considered important [1] based on the assump-tion that the goals of users influence their information needs. Along with theaforementioned modeling dimensions, environmental aspects are considered akey issue when modeling the user for improving the interaction between humanand computer.

Besides these more generic aspects of user modeling, there are also some ef-forts in standardizing user model related aspects, mostly in application-specificareas. The vCard specification and X.500, known as LDAP, are related stan-dards. The IMS Learner Information Package (LIP) specification offers a datamodel that describes characteristics of a user needed for the general purpose ofrecording and managing learning related history, goals and accomplishments. Inaddition, the IEEE Public And Private Information (PAPI) specification wascreated to represent student records.

The above standards are well known, but suffer from some drawbacks. vCardis suited for light weight user profiles like contact information or directories.While LDAP allows storing user information as entries made up of attributes, thedirectory schemas place restrictions on the attribute types that must be, or areallowed to be, contained in an entry. IMS and PAPI are more generic and basedon standards like XML. However, they are not conceptually extensible. A unifieduser profiling format needs to take into account the domain knowledge thatmight be required for various applications. In order to support personalizationacross multiple systems, a broader understanding of the user is required as isalso discussed in [2, 3].

3 The Unified User Context Model

The UUCM is a user context model that is structured along different dimensionsand captures the fact that the user interacts with systems in different workingcontexts by structuring the model accordingly. In order to support cross-systempersonalization, the model has to be flexible and extensible enough to deal withthe variations in personalization approaches and to incorporate the various as-pects relevant for capturing the users’ characteristics and his current situation.The main building blocks for the UUCM is an extensible set of facets represent-ing the characteristics of the user and his current context. We use the term facetsinstead of properties, because we do not only capture attribute value pairs, butalso probabilities and qualifiers for facet values, thus giving a richer descriptionas it is typical for frame-based languages. An extensible set of UUCM dimensions

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enables the structuring of the facets into groups of user characteristics (e.g. facetsrelated to cognitive pattern). In the context of UUCM, qualification of namesas well as values of the facets is a crucial aspect. Both names and values mayrefer to vocabularies or ontologies, giving the possibility to connect to sharedvocabularies, thus simplifying interpretation in a global (cross-system) context.Each UUCM facet is described by the following properties, part of which areoptional:

– Facet name - name of the UUCM facet to be described;– Facet qualifier - used to bind the facet to a defining vocabulary or ontology;– Facet value - value of the facet, which can be a simple literal as well a

reference to a structured resource depending on the domain;– Value qualifier - a qualifier for the value(s) of the facet, i.e. it points to the

vocabulary or ontology the value is taken from;– Value probability - a weight reflecting the probability of the facet value;– Facet dimension - each facet is assigned to one of the UUCM dimensions.

The UUCM defines a meta-model for the concrete dimensions and facets usedin the description of a user context model. For the cross-system personalizationapproach, that we are aiming for, it is assumed that this user context meta-model is published as a shared ontology and all participating systems rely onthis model. In support of the UUCM, other ontologies are required: a facetontology that defines the different facets, a dimension ontology that defines facetdimensions and, optionally, also ontologies for the facet values. More details areavailable in [3]. Information for filling profiles based on UUCM context modelsare gathered by observing the user interactions, such as items bought, ratingprovided by users on items, keywords searched, etc. An alternative form to collectvalues for the facets is to ask the user to fill in an initial form, where the usercan enter information about his/her characteristics. The main problem of thisprocess is that its validity depends on whether the users are willing to updatethe information regularly. A possible solution is to integrate/update the explicitsinterests given by the user with the automatic generation of profiles exploitingsupervised learning techniques [5]. An example of collecting information for theRelationship Dimension can be found in [6].

4 UUCM in a Real World Cross System Scenario

There are three objectives which cross-system personalization needs to address:1) broader user models that can cope with the variety in user modeling,2) handling heterogeneous personalization systems and approaches, and3) giving more control to the user. In line with these objectives, we claim thatuser profiles should be stored closer to the user. However, maintaining user pro-files on the user’s side presents some challenges. Interacting with multiple in-formation systems may lead to a large amount of interaction data. Since theindividual system best understands the local interactions this should be donewithin the individual personalization engine and only higher level descriptions

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of users should be exchanged between the information system and the unifieduser profile, which we call the Context Passport. The exchange of such informa-tion requires a negotiation between activities that an information system canperform and those activities that the user context outlines. The Cross SystemCommunication Protocol (CSCP) provides a platform for such negotiations.

4.1 Example Scenario for Unified Profiling in Instant Messaging

In an examle scenario, two Instant Messaging (IM) applications: the MSN andYahoo Messenger are considered. Essentially the user profiles of these IM net-works are lists of contacts that a person is explicitly connected with. While theprofiles of these applications focus on modeling relationship aspects, the pro-files have a different structure to model this user information. MSN Messengerallows user to have custom names, but has predefined categories for classifyingcontacts (Friends, Family, etc). Yahoo Messenger does not allow custom names,but allows creation of new categories. Furthermore, with MSN Messenger, itis possible to have a person on your list, yet to block them from contactingyou. Yahoo has different structure, and to block or ignore a contact, this per-son has to be deleted from the list and then added to a separate ignore list.Most user profile formats like PAPI and IMS will fail to store a unified profilecompletely.

As an concrete example, we take up a simple user profile for a fictitioususer John’s MSN and Yahoo (Figure 2) profiles. Both these models use com-mon concepts, which can be represented by a common vocabulary consisting ofconcepts im:Contact, im:Contact-List, im:Group related by relationships dis-

Fig. 1. User Profile Ontology for MSN and Yahoo Messenger

Fig. 2. (a)John’s Profile for MSN and Yahoo(b)John’s Yahoo Profile in UUCM

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cussed in Section 3, as shown in Figure 1(a),(b). Analyzing the domain forIM user profiles, we reach a common model shown in Figure 1(c), composedof only two facets. The same common model can be used for AOL, ICQ andother IM applications with minor modifications to the common vocabulary.Thus this model represents the domain model for the IM domain. Further ad-ditions to the model are possible, but for this example, we assume the pro-file to be composed of only a categorized list of contacts. Using this under-standing, we can represent both the profiles in the UUCM format. Figure 2(b)shows how the Yahoo profile can be represented. The MSN profile can be simi-larly represented. We note that the profiles for these applications lie completelyin the Relationship dimension. By using a common format for representingusers, these two applications can more easily interoperate, and one applica-tion can connect to both networks while maintaining a common profile. Similarmodels can be constructed for eCommerce websites and personalized contentproviders.

5 Conclusions

This paper proposes the use of a unified user profile format, which can be ex-tended for use with multiple applications, and potentially be used to exchangecommon information between multiple systems. The UUCM provides a basisfor the realization of cross-system personalization approaches that enable theexchange and reuse of user profiles across different systems. UUCM componentsrefer to common vocabularies or ontologies in order to give the possibility tointerpret the user models in the different contexts.

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