On Efficient Recommendations for Online Exchange Markets. Zeinab Abbassi, Laks V. S. Lakshmanan: ICDE 2009:712-723. M otivation. peerflix.com- exchange movies readitswapit.co.uk- exchange books oddshoe.org- exchange shoes Applications on online social networks like Facebook.
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Zeinab Abbassi, Laks V. S. Lakshmanan: ICDE 2009:712-723
peerflix.com- exchange movies
readitswapit.co.uk- exchange books
oddshoe.org- exchange shoes
Applications on online social networks like Facebook.
Simple exchange market- restricted to a set of swap recommendations
Exchange markets with short cycles- short exchange cycles of up to length k
Probabilistic exchange markets- probability associated with each user engaged in the transaction
Optimize the number of items exchanged.
Cycle cover problem: Given a graph and a subset of marked elements (nodes or edges) find a minimum length set of cycles whose union contain all the marked elements.
ExchangeMarket problems can be modeled as a cycle cover problems.
Content based- user will be recommended
items similar to the ones the user preferred in the past
Collaborative- The user will be recommended
items that people with similar tastes and
preferences liked in the past
• Hybrid approaches: combination of both methods
Kidney Exchange problem similar to simple market exchange. If exchanges are restricted to swaps, can be solved using maximum weighted perfect
Algorithm for generating exchange cycles is run periodically
User accounts, item lists and wish lists are updated
User does not own multiple copies of an item and does not wish for multiple copies of an item.
Set of feasible exchanges changes with time
Given a set of users U with the item lists Su and wish lists Wu for each user u ∈ U, find pairs of users such that items on the item list of one user appear on the wish list of another user.
If we restrict ourselves to swaps, none of the users may be satisfied.
Find an optimal set of conflict-free cycles of length < k
The Simple Market problem, the probabilistic market problem and the Kidney exchange problem for cycles of length > 2 are NP-Complete.
A heuristic algorithm and three approximation algorithms have been developed which use a directed graph representation
Run the greedy algorithm to find a set of cycles B and then run the local search algorithm starting from cycles in B.
|B|: number of cycles found
OPT: weight of the optimal solution
k : maximum length of a cycle
Algorithms implemented using MATLAB and tested using synthetic data sets.
Performance of Maximal is comparable to others and is by far the most efficient.
Investigations on real data sets
Further exploration of probabilistic exchange markets
Analysis of exchange markets which award points for giving away items which can be redeemed later when another user needs them.
Another research direction is to suggest recommendations which improve user experience by helping users find surprisingly good items.
Zeinab Abbassi, Sihem Amer-Yahia, Laks V. S. Lakshmanan, Sergei Vassilvitskii, Cong Yu: Getting recommender systems to think outside the box. RecSys 2009: 285-288