ReputationPro
Authors: Zhang Haibin , Wang Yan , Zhang Xiuzhen , Lim Ee-Peng 
Published: January 2015

In e-commerce environments, the trustworthiness of a seller is utterly important to potential buyers, especially when a seller is not known to them. Most existing trust evaluation models compute a single value to reflect the general trustworthiness of a seller without taking any transaction context information into account. With such a result as the indication of reputation, a buyer may be easily deceived by a malicious seller in a transaction where the notorious
value imbalance
problem is involved—in other words, a malicious seller accumulates a high-level reputation by selling cheap products and then deceives buyers by inducing them to purchase more expensive products.

In this article, we first present a trust vector consisting of three values for contextual transaction trust (CTT). In the computation of CTT values, three identified important
context dimensions
, including Product Category, Transaction Amount, and Transaction Time, are taken into account. In the meantime, the computation of each CTT value is based on both past transactions and the forthcoming transaction. In particular, with different parameters specified by a buyer regarding context dimensions, different sets of CTT values can be calculated. As a result, all of these trust values can outline the reputation profile of a seller that indicates the dynamic trustworthiness of a seller in different products, product categories, price ranges, time periods, and any necessary combination of them. We name this new model
ReputationPro
. Nevertheless, in
ReputationPro
, the computation of reputation profile requires new data structures for appropriately indexing the precomputation of aggregates over large-scale ratings and transaction data in three context dimensions, as well as novel algorithms for promptly answering buyers’ CTT queries. In addition, storing precomputed aggregation results consumes a large volume of space, particularly for a system with millions of sellers. Therefore, reducing storage space for aggregation results is also a great demand.

To solve these challenging problems, we first propose a new index scheme
CMK-tree
by extending the two-dimensional
K-D-B-tree
that indexes spatial data to support efficient computation of CTT values. Then, we further extend the
CMK-tree
and propose a
CMK-tree

RS

approach to reducing the storage space allocated to each seller. The two approaches are not only applicable to three context dimensions that are either linear or hierarchical but also take into account the characteristics of the transaction-time model—that is, transaction data is inserted in chronological order. Moreover, the proposed data structures can index each specific product traded in a time period to compute the trustworthiness of a seller in selling a product. Finally, the experimental results illustrate that the
CMK-tree
is superior in efficiency of computing CTT values to all three existing approaches in the literature. In particular, while answering a buyer’s CTT queries for each brand-based product category, the
CMK-tree
has almost linear query performance. In addition, with significantly reduced storage space, the
CMK-tree

RS

approach can further improve the efficiency in computing CTT values. Therefore, our proposed
ReputationPro
model is scalable to large-scale e-commerce Web sites in terms of efficiency and storage space consumption.