Evaluating an item based on user reputation information

1. A system for evaluating content items served by the system to multiple users who initiate sharing events regarding the content items, the system comprising:

a processor configured to:

receive sharing event data reflecting the sharing events initiated by the multiple users, including, for each content item, an initial sharing event initiated by an initial user;

determine, for each content item, a time-based order of the sharing events reflected in the sharing event data;

generate a graph based on the sharing event data, the graph comprising:

a separate node corresponding to each of the multiple users that initiated a sharing event; and

for each content item, for each given user that initiated a sharing event for the content item, other than the initial user who initiated the initial sharing event for the content item, at least one directed link from the given user's corresponding node to a node corresponding to another user who initiated a sharing event for the content item before the given user;

determine user reputation scores for the multiple users based on connectivity of the graph; and

for each content item, combine the user reputation scores of the users that initiated sharing events for the content item to produce a score for the item; and

a memory coupled to the processor and configured to provide the processor with instructions.

2. The system of claim 1 , wherein the sharing event data includes multiple preference events initiated by the multiple users while viewing the content items.

3. The system of claim 2 , wherein each preference event is one of:

a positive preference event; and

a negative preference event.

4. The system of claim 1 , wherein the sharing event data includes at least one sharing event in which one of the multiple users:

viewed a content item served by the system; and

activated a control served by the system to accompany the content item;

wherein activation of the control caused the content item to be shared with one or more other users.

5. The system of claim 1 , wherein the processor is further configured to log the sharing event data by recording, for each sharing event:

an identity of the user that initiated the sharing event;

a timestamp of the sharing event; and

an identity of the content item associated with the sharing event.

6. The system of claim 5 , wherein:

the system further comprises a database; and

sharing events of different types are stored in separate logs of the database.

7. The system of claim 5 , wherein the sharing events are stored as an ordered list ordered by the timestamps.

8. The system of claim 1 , wherein:

determining a time-based order comprises, for each sharing event initiated by a given user for a given content item, identifying one or more of a pre-sharer and a post-sharer;

a pre-sharer is a user who initiated a sharing event for the given content item before the given user; and

a post-sharer is a user who initiated a sharing event for the given content item after the given user.

9. The system of claim 1 , wherein generating the graph comprises:

for each content item, for each given user that initiated a sharing event for the content item, other than the initial user who initiated the initial sharing event for the content item, graphing directed links from the given user's corresponding node to nodes corresponding to all other users who initiated sharing events for the content item before the given user.

10. The system of claim 1 , wherein generating the graph comprises:

for each content item, for each given user that initiated a sharing event for the content item, other than the initial user who initiated the initial sharing event for the content item, graphing a single directed link from the given user's corresponding node to the one node corresponding to the user who initiated a sharing event for the content item most recently in time before the given user.

11. The system of claim 1 , wherein generating the graph comprises replacing multiple directed links from a first user to a second user with a single link.

12. The system of claim 1 , wherein generating the graph comprises:

weighting each directed link according to a type of sharing event between the users corresponding to the nodes connected by the directed link, wherein directed links corresponding to different types of sharing events have different weights.

13. The system of claim 1 , wherein generating the graph comprises generating the graph for only one type of sharing event, and wherein the processor is further configured to:

repeat said generating to generate a second graph for sharing events of a second type.

14. The system of claim 1 , wherein determining user reputation scores comprises:

assembling a specialized connectivity matrix H based on connectivity of the graph, wherein:

i and j represent different users in the multiple users;

D i is a set of content items for which user i initiated sharing events;

P ij is a subset of D i for which user j initiated a sharing event for a given content item before user i initiated a sharing event for the given content item;

R is is a number of users who initiated sharing events for content item s before user i; and

H

ij

=

1



D

i



⁢

∑

s

∈

P

ij

⁢

⁢

1



R

is



.

15. The system of claim 14 , wherein determining user reputation scores further comprises:

assembling a matrix M representing connectivity of the graph, wherein:

N is a total number of nodes of the graph;

A is a matrix having a column for each node, wherein every column corresponding to a node at the origin of a directed link comprises the value zero, and every column corresponding to a node that is not at the origin of any directed link comprises the value one;

1 is the unit matrix;

α is a value between approximately 0.8 and approximately 1.0; and

M

=

α

⁢

⁢

H

+

α

⁢

⁢

A

+

1

-

α

N

-

1

;

 and

calculating a maximal eigenvector d such that Md=d;

wherein eigenvector d comprises the user reputation scores.

16. A method for evaluating content items served by the system to multiple users who initiate sharing events regarding the content items, the method comprising:

receiving sharing event data reflecting the sharing events initiated by the multiple users, including, for each content item, an initial sharing event initiated by an initial user;

determining, with a processor and for each content item, a time-based order of the sharing events reflected in the sharing event data;

generating a graph based on the sharing event data, the graph comprising:

a separate node corresponding to each of the multiple users that initiated a sharing event; and

for each content item, for each given user that initiated a sharing event for the content item, other than the initial user who initiated the initial sharing event for the content item, at least one directed link from the given user's corresponding node to a node corresponding to another user who initiated a sharing event for the content item before the given user;

determining user reputation scores for the multiple users based on connectivity of the graph; and

for each content item, combining the user reputation scores of the users that initiated sharing events for the content item to produce a score for the item.

17. A non-transitory computer program product for evaluating content items served by the system to multiple users who initiate sharing events regarding the content items, the computer program product being embodied in a computer readable storage medium and comprising computer instructions for:

receiving sharing event data reflecting the sharing events initiated by the multiple users, including, for each content item, an initial sharing event initiated by an initial user;

determining, for each content item, a time-based order of the sharing events reflected in the sharing event data;

generating a graph based on the sharing event data, the graph comprising:

a separate node corresponding to each of the multiple users that initiated a sharing event; and

for each content item, for each given user that initiated a sharing event for the content item, other than the initial user who initiated the initial sharing event for the content item, at least one directed link from the given user's corresponding node to a node corresponding to another user who initiated a sharing event for the content item before the given user;

determining user reputation scores for the multiple users based on connectivity of the graph; and

for each content item, combining the user reputation scores of the users that initiated sharing events for the content item to produce a score for the item.