information retrieval in folksonomies nikos sarkas social information systems seminar dcs,...
TRANSCRIPT
Information Retrieval in Folksonomies
Nikos Sarkas
Social Information Systems Seminar
DCS, University of Toronto, Winter 2007
Social Resource Sharing
The del.icio.us paradigm. Users store links to web pages of interest along
with arbitrary, user-specified tags in a server. The model is independent of the resource
being shared. Music (Last.fm) Photos (Flickr) Publications (CiteULike) …
Folksonomies
Folk+taxonomy. Taxonomies are rigid, carefully engineered
structures. Folksonomies are flexible, time-variant
structures that result from the converging use of the same vocabulary.
Interesting Problems
A wealth of interest problems in this setting: Search result ranking Personalization Recommendation Trend detection Community extraction …
Keyword Search
Result ranking is currently naïve. Resources associated with tags matching the
keywords are returned in reverse chronological order.
TF/IDF not useful in this context. What about PageRank™?
PageRank Algorithm
Let be a collection of web pages. Then
Many alternatives in interpreting the
PageRank of a web page. Iterative computation
1,..., nP P
( )
( )( )
( )j i
ji
P M P j
PR PPR P
L P
1 (1 )t tw dAw d p
Formalism
Entities of a Folksonomy Users U Tags T Resources R Assignments Y
Representation Tripartite undirected hypergraph G=(V,E), V=UUTUR, E={ (u,t,r) | (u,t,r) in Y }
Adapted PageRank
Flatten the Folksonomy graph.
Apply PageRank. A resource tagged with
important tags by important users becomes important. Symmetrically for tags and users.
2 1
1
11
U1
U2 T2
T1 R1
R2
U1
U2
T1
T2
R1
R2
12
1
1 1
Adapted PageRank
Important! The flat Folksonomy graph is undirected.
Part of the weight that goes through an edge at time t, will flow back at time t+1.
Results are similar to an edge degree ranking. They are identical for d=1.
FolkRank
Topic specific ranking in Folksonomies. A topic is defined through preference vector A topic can be defined through tags,
resources or users. Let be the Adapted PageRank vector for
d=1. Let be the Adapted PageRank vector for
d<1 and a specified preference vector. The FolkRank vector is .
p
0w
1w
1 0:w w w
Results
Adapted PageRank, d=1
Results
Adapted PageRank vs FolkRank
Extensions
Resource recommendation. Similar tag suggestion. User introduction. Trend detection.