This document introduces a privacy preference manager for the social semantic web. It proposes a lightweight vocabulary called PPO for defining fine-grained privacy preferences over RDF data. PPO allows users to specify restrictions on what information is shared, conditions on when it is shared, access control privileges, and SPARQL queries to test requesters. The privacy preference manager applies these preferences to filter a user's FOAF profile when another user requests to view it. Future work aims to extend PPO's expressiveness and the manager's functionality.

1. Digital Enterprise Research Institute www.deri.ie
A Privacy Preference Manager for
the Social Semantic Web
Owen Sacco and Alexandre Passant
firstname.lastname@deri.org
SPIM 2011 – Bonn, Germany Monday 24th October 2011
Copyright 2011 Digital Enterprise Research Institute. All rights reserved.
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2. Introduction
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 Increase in shared personal information on the Social
Web raised awareness about privacy
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3. Introduction
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 Recent Study1 shows:
 Privacy became a concern in Social Networks (SN) when private
news was publicly shared
 SNs provided third party with user’s information
 Most users are aware of privacy settings and have set them at
least since 2009
1Danah Boyd and EszterHargittai. Facebook privacy settings. Who cares? First Monday. August 2010.
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4. Current Limitations
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 Social Web applications provide system default privacy
settings
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5. Use Case
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 A FOAF based Social Network Network
Protecting a FOAF based Social
 Users feel more confident to publish their information
 Users would be in full control
– Which specific information can be shared and to whom
 Granting access based on interest and not only to friends in
contact lists
– Eg: Provide my phone number only to DERI colleagues without
being in a friend or group list called DERI
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6. PPO Overview
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 A light weight vocabulary for defining fine-grained
privacy preferences for RDF data
 A privacy preference contains:
 Which resource, statement or graph must be restricted
 A condition that must be satisfied
 The access control privilege (defined using WAC)
 A SPARQL query that tests whether a user requesting
information matches a graph pattern
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7. PPO Overview
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ppo:PrivacyPreference ppo:hasAccessSpace ppo:AccessSpace ppo:hasAccessQuery
This
rdfs:Literal
rdfs:Literal represents a
SPARQL
query as a
String.
ppo:appliesToResource ppo:appliesToStatement ppo:appliesToNamedGraph ppo:hasCondition
ppo:hasAccess
rdfs:Resource rdf:Statement trix:Graph ppo:Condition
acl:Access
ppo:resourceAsSubject ppo:resourceAsObject ppo:classAsSubject ppo:classAsObject ppo:hasLiteral ppo:hasProperty
rdf:Propert
rdfs:Resource rdfs:Resource rdfs:Class rdfs:Class rdfs:Literal
y
Restrictions Conditions Access Test Queries Access Control Privileges
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8. PPO Overview
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 Example:
 Provide my phone number only to DERI colleagues
PREFIX ppo: <http://vocab.deri.ie/ppo#> .
PREFIX ex: <http://example.org/> .
ex:pp1 a ppo:PrivacyPreference;
ppo:hasCondition
[ ppo:hasPropertyfoaf:phone ];
ppo:hasAccessacl:Read;
ppo:hasAccessSpace
[ ppo:hasAccessQuery
"ASK {?xfoaf:workplaceHomepage<http://www.deri.ie>}"].
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9. PPO Formal Model
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 Definition 1: Restrictions
 Resource
– Identified by its own URI
∀St(AssignAccess(U,A) ∧ (Subject(U,St) ∨ Predicate(U,St) ∨
Object(U,St)) ⇒ AssignAccess(St,A))
 Statement
– Consists of <subject, predicate, object>
∀St((AssignAccess(S,A) ∧ AssignAccess(P,A) ∧
AssignAccess(O,A)) ∧ (Subject(S,St) ∧ Predicate(P,St) ∧
Object(O,St)) ⇒ AssignAccess(St,A))
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10. PPO Formal Model
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 Named Graph
– A name denoted by a URI
– A set of statements mapped to this name
∀St(AssignAccess(NG,A) ∧ RDFGraph(St,NG) ⇒
AssignAccess(St,A))
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11. PPO Formal Model
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 Definition 2: Conditions
 Resource As Subject
– A resource’s URI identified as a statement’s Subject
∀St(AssignAccess(U,A) ∧ Subject(U,St) ⇒ AssignAccess(St,A))
 Resource As Object
– A resource’s URI identified as a statement’s Object
∀St(AssignAccess(U,A) ∧ Object(U,St) ⇒ AssignAccess(St,A))
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12. PPO Formal Model
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 Class As Subject
– An instance of a class defined as a statement’s Subject
∀St(AssignAccess(C,A) ∧ RDFType(U,C) ∧ Subject(U,St) ⇒
AssignAccess(St,A))
 Class As Object
– An instance of a class defined as a statement’s Object
∀St(AssignAccess(C,A) ∧ RDFType(U,C) ∧ Object(U,St) ⇒
AssignAccess(St,A))
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13. PPO Formal Model
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 Definition 3: Access Control Privilege
 An access control privilege defines the read and/or write
privilege
AccessControl = {read,write}
 Definition 4: Access Space
 Contains an access query that checks if a requester satisfies
specific attributes
AccessSpace = {accessquery1, ..., accessqueryn}
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14. PPO Formal Model
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 Definition 5: A Privacy Preference
 The set of all: Restrictions, Conditions, AccessControl and
AccessSpace
PrivacyPreference ⊆ Restrictions ∪ Conditions ∪
AccessControl ∪ AccessSpace
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15. PPO Formal Model
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 Definition 6: Applying Privacy Preferences
 A requester requests personal information
 This request is matched to the correct privacy preference
– i.e. the restrictions
∀P((Statement(St,P) ∨ Resource(R,P) ∨ NamedGraph(NG,P)) ⇒
ApplyPrivacyPreference(P))
 A mapping is done between the restricted statements (RS) and
the condition statements (CS)
M : RestrictedStatements(RS) →ConditionStatements(CS)
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16. PPO Formal Model
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 If M = false THEN ¬ApplyPrivacyPreference(P)
 If ApplyPrivacyPreference(P), AccessSpace(Q) is executed on
the requester’s information
 If AccessSpace(Q) = true THEN AccessControl(A) is granted to
the requester
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17. MyPrivacyManager
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 MyPrivacyManager provides two main tasks:
 A user creates his/her privacy preferences
 A requester logs in to the other user’s MyPrivacyManager which
in turn will view a faceted profile
– filtered based on the privacy preferences
User A
MyPrivacy Manager
WebID
Private FOAF Profile
User B
Privacy
Requester
Preferences
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18. MyPrivacyManager
Digital Enterprise Research Institute www.deri.ie
foafssl.org
WebID Authentication Service
Social Semantic Data
SSL Certificate Confirmation Request RDF DATA
MyPrivacyManager
WebID FOAF URI RDF Data Retriever &
Authenticator Parser
SSL Certificate Confirmation FOAF
Privacy Preferences
Privacy
Privacy Enforcer
Logs In Preferences
Preferences
User
Interface
Created Created
User Privacy Preferences
Privacy Created
Privacy Privacy
Creator
Preferences Preferences
Privacy Preferences
Preferences
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19. MyPrivacyManager
Digital Enterprise Research Institute Attributes
www.deri.ie
which a
FOAF requester
must satisfy
(AccessQuery
)
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20. MyPrivacyManager
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PREFIX ppo: <http://vocab.deri.ie/ppo#> .
PREFIX ex: <http://vmuss13.deri.ie/> . Provenance
ex:preference1 a ppo:PrivacyPreference; Information
foaf:maker<http://foaf.me/ppm_usera#me>; Restrictions
dc:title "Restricting access to my personal information”;
dc:created "2011-06-01T13:32:59+02:00”;
ppo:appliesToStatement :Statement1;
:Statement1
rdf:subject<http://vmuss13.deri.ie/foafprofiles/terraces#me>;
rdf:predicate<http://xmlns.com/foaf/0.1/name>;
rdf:object "Alexandre Passant”;
ppo:appliesToStatement :Statement2;
:Statement2
rdf:subject<http://vmuss13.deri.ie/foafprofiles/terraces#me>;
rdf:predicate<http://xmlns.com/foaf/0.1/nick>;
rdf:object "terraces”;
Access Space
Access Control Privilege
ppo:assignAccess acl:Read;
ppo:hasAccessSpace [
ppo:hasAccessQuery "ASK { ?xfoaf:workplaceHomepage<http://www.deri.ie> }"].
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21. MyPrivacyManager
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FOAF Profiles
foafssl.org
WebID Authentication Service
User B
User A
User A
SSL Certificate Confirmation Request RDF DATA
Request RDF DATA
MyPrivacyManager
WebID RDF Data Retriever &
Authenticator Parser
SSL Certificate Confirmation Query AccessQuery Result
RDF Data
Request Query
Privacy Preferences
Privacy
Enforcer
(Requester) Filtered Privacy Preferences
Logs In
User FOAF Data Preference
Interface
Filtered
User B Privacy Preferences
FOAF
Creator
Profile
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22. Future Work
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 Extending PPO:
 Conjunctive and disjunctive properties for Conditions
 Specify the type of environment, i.e. closed or open environment
 Cater for more fuzziness in privacy preferences
– Example: Allow access to my party invite to all those that live (have
coordinates) around Galway
 Extending MyPrivacyManager:
 Grouping of interests under categories
 Assert trustworthiness of source and requester’s data
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23. Links
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 PPO Namespace URI: http://vocab.deri.ie/ppo#
 Screencasts
 Creating Privacy Preferences: http://bit.ly/p0N1Vi
 Viewing Filtered FOAF Profiles: http://bit.ly/qiAdxT
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