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CHOOSING THE RIGHT CROWD
EXPERT FINDING IN SOCIAL NETWORKS
Alessandro Bozzon
Marco Brambilla
Stefano Ceri
Matteo Silvestri
Giuliano Vesci
Politecnico di Milano
Dipartimento di Elettronica, Informazione e BioIngegneria
Problems and terms• Human Computation:
• Computation carried out by groups of humans (examples: collaborative filtering, online auctions, tagging, games with a purpose)
• Crowd-sourcing: • The process of building a human computation using computers as
organizers, by organizing the computation as several tasks (possibly with dependences) performed by humans
• Crowd-searching: • A specific task consisting of searching information
• Crowd-sourcing Platform:• A software system for managing tasks, capable of organizing tasks,
assigning them to humans, assembling and processing returned results (such as Amazon Mechanical Turk, Doodle)
• Social Platform:• A platform where humans perform social interactions (such as Facebook,
Twitter, LinkedIn)
The market
Why Crowd-search?• People do not trust web search completely
• Want to get direct feedback from people
• Expect recommendations, insights, opinions, reassurance
And given that crowds spend times on social networks….
• Our proposal is to use social networks and Q&A websites as crowd-searching platforms, in addition to crowdsourcing platforms
• Example: search tasks
From social workers to communities
• Issues and problems• Motivation of the responders
• Intensity of social activity of the asker
• Topic appropriateness
• Timing of the post (hour of the day, day of the week)
• Context and language barrier
Crowd-searching after conventional search
• From search results to friends and experts feedback
Social Platform
initial query
Human SearchSystem
SearchSystem
Social PlatformSocial Platform
Example: Find your next job (exploration)
Example: Find your job (social invitation)
Example: Find your job (social invitation)
Selected data items can be transferred to the crowd question
Find your job (response submission)
Crowdsearcher results (in the loop)
WWW2012 – THE MODEL
Task management problemsTypical crowdsourcing problems:
• Task splitting: the input data collection is too complex relative to the cognitive capabilities of users.
• Task structuring: the query is too complex or too critical to be executed in one shot.
• Task routing: a query can be distributed according to the values of some attribute of the collection.
Plus:
• Platform/community assignment: a task can be assigned to different communities or social platforms based on its focus
Task Design• Which are the input objects of the crowd interaction?
• Should they have a schema (set of fields, each defined by a name and a type)?
• Which operations should the crowd perform?
• Like, label, comment, add new instances, verify/modify data, order, etc.
• How should the task be split into micro-tasks assigned to each person?
How should a specific object be assigned to each person?
• How should the results of the micro-tasks be aggregated?
• Sum, Average, Majority voting, etc.
• Which execution interface should be used?
Operations• In a Task, performers are required to execute logical operations on input objects
• e.g. Locate the faces of the people appearing in the following 5 images
• CrowdSearcher offers pre-defined operation types:• Like: Ask a performer to express a preference (true/false)
• e.g. Do you like this picture?• Comment: Ask a performer to write a description / summary / evaluation
• e.g. Can you summarize the following text using your own words?• Tag: Ask a performer to annotate an object with a set of tags
• e.g. How would you label the following image?• Classify: Ask a performer to classify an object within a closed-set of alternatives
• e.g. Would you classify this tweet as pro-right, pro-left, or neutral? • Add: Ask a performer to add a new object conforming to the specified schema
• e.g. Can you list the name and address of good restaurants nearby Politecnico di Milano?• Modify: Ask a performer to verify/modify the content of one or more input object
• e.g. Is this wine from Cinque Terre? If not, where does it come from? • Order: Ask a performer to order the input objects
• e.g. Order the following books according to your taste
Splitting Strategy• Given N objects in the task
• Which objects should appear in each MicroTask?• How many objects in each MicroTask?• How often an object should appear in MicroTasks?• Which objects cannot appear together?• Should objects be presented always in the same order?
Assignment Strategy• Given a set of MicroTasks, which performers are assigned to them?
• Online assignment• Micro Tasks dynamically assigned to performers
• First come / First served• Based on a choice of the performer
• Offline assignment• MicroTasks statically assigned to performers
• Based on performers’ priority• Based on matching
• Invitation• Send an email to a mailing list• Publish a HIT on Mechanical Turk (dynamic)• Create a new challenge in your game• Publish a post/tweet on your social network profile• Publish a post/tweet on your friends' profile
Deployment: search on the social network
• Multi-platform deployment
Embedded application
Social/ Crowd platformNative
behaviours
External application
Standalone application
API
Embedding
Community / Crowd
Generated query template
Native
Deployment: search on the social network• Multi-platform deployment
Deployment: search on the social network• Multi-platform deployment
Deployment: search on the social network• Multi-platform deployment
Deployment: search on the social network• Multi-platform deployment
Crowdsearch experiments• Some 150 users
• Two classes of experiments:• Random questions on fixed topics: interests (e.g. restaurants in the vicinity of
Politecnico), to famous 2011 songs, or to top-quality EU soccer teams
• Questions independently submitted by the users
• Different invitation strategies:• Random invitation
• Explicit selection of responders by the asker
• Outcome• 175 like and insert queries
• 1536 invitations to friends
• 230 answers
• 95 questions (~55%) got at least one answer
Experiments: Manual and random questions
Experiments: Interest and relationship
• Manually written and assigned questions are consistently more responded in time
Experiments: Query type• Engagement depends on the difficulty of the task
• Like vs. Add tasks:
Experiment: Social platform• The question enactment platform role
• Facebook vs. Doodle
Experiment: Posting time• The question enactment platform role
• Facebook vs. Doodle
EDBT 2013
Problem
• Ranking the members of a social group according to the level of knowledge that they have about a given topic
• Application: crowd selection (for Crowd Searching or Sourcing)
• Available data• User profile • behavioral trace that users leave behind them through
their social activities
Considered Features• User Profiles
• Plus Linked Web Pages
• Social Relationships• Facebook Friendship• Twitter mutual following relationship• LinkedIn Connections
• Resource Containers• Groups, Facebook Pages• Linked Pages• Users who are followed by a given user are resource containers
• Resources• Material published in resource containers
Feature Organization Meta-Model
Example (Facebook)
Example (Twitter)
Resource Distance• Objects in social graph organized according to their
distance with respect to the user profile• Why? Privacy, Computational Cost, Platform Access Constraints
Distance Resource
0 Expert Candidate Profile
1
Expert Candidate owns/create/annotates Resource
Expert Candidate relatedTo Resource Container
Expert Candidate follows UserProfile
2
Expert Candidate follows UserProfile relatedTo Resource Container
Expert Candidate relatedTo Resource Container contains Resource
Expert Candidate follows UserProfile owns/create/annotates Resource
Expert Candidate follows UserProfile follows UserProfile
Distance interpretationDistance Resource
0 Expert Candidate Profile
1
Expert Candidate owns/create/annotates Resource
Expert Candidate relatedTo Resource Container
Expert Candidate follows UserProfile
2
Expert Candidate follows UserProfile relatedTo Resource Container
Expert Candidate relatedTo Resource Container contains Resource
Expert Candidate follows UserProfile owns/create/annotates Resource
Expert Candidate follows UserProfile follows UserProfile
Resource Processing
• Extraction from Social Network APIs
• Extraction of Text from linked Web Pages• Alchemy Text Extraction APIs
• Language Identification
• Text Processing• Sanitization, tokenization,
stopword, lemmatization
• Entity Extraction and Disambiguation• TagMe
Method – Resource Score
• tf(t,r) term frequency -- irf(t) inverse resource frequency of t• ef(e,r) entity frequency -- eir(e) inverse entity frequency of e
we(e,r) relevance of entity in resource
Entity Component Weighting
Method: Expert Score
• Experts are ranked according to score(q,ex)
Resource weight for given expertise
Resource Score
Window Size
Dataset• 7 kinds of expertises
• Computer Engineering, Location, Movies & TV, Music, Science, Sport, Technology & Videogames
• 40 volunteer users (on Facebook & Twitter & LinkedIN)
• 330.000 resources (70% with URL to external resources)
• Groundtruth created trough self-assessment• For expertise need, vote on 7 Likert Scale• EXPERTS expertise above average
Distribution of Expertise and Resources
• High # Resources on Facebook and Twiitter
• Higher # users on Facebook
• Avg Expertise ~ 3.5 / 7• High Music and Sport
Expertise• Low Location Expertise
Metrics• We obtain lists of candidate experts and assess them
against the ground truth, using:• For precision:
• Mean Average Precision (MAP)• 11-Point Interpolated Average Precision (11-P)
• For ranking:• Mean Reciprocal Rank (MRR) – for the first value• Normalized Discounted Cumulative Gain (DCG) – for more values, can
be set @N for the first N values
Metrics improves with resources• But it comes with a cost
Friendship Relationship not useful• Inspecting friend’s resources does not improve metrics!
Social Network Analysis
• a
Comparison of the results obtained with All the social networks, or separately by FaceBook, TWitter, and LinkedIn.
Main Results• Profiles are less effective than level-1 resources
• Resources produced by others help in describing each individual’s expertise
• Twitter is the most effective social network for expertise matching – sometimes it outperforms the other social networks• Twitter most effective in Computer Engineering, Science, Technology &
Games, Sport
• Facebook effective in Locations, Sport, Movies & TV, Music• Linked-in never very helpful in locating expertise
WWW 2013Reactive Crowdsourcing
Main Message• Crowd-sourcing should be dynamically adapted• The best way to do so is through active rules• Four kinds of rules:
execution / object / performer / task control • Guaranteed termination• Extensibility