Zinayida Petrushyna, Ralf Klamma

1. First steps in social network
Zina
Petrushyna analysis
Ralf Klamma
Workshop
Terchova, June 2009
Zinayida Petrushyna, Ralf Klamma
Chair for Information Systems and Databases,
RWTH Aachen University, Germany
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-1

2. Motivation
Old theories New theory
• Actual process •Knowledge is continual
Zina
Petrushyna
Ralf Klamma
• Learning happens inside • Cognitive operations are done
by machines
• Instructional design
• Network pedagogy
pedagogy
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-2

3. Fundamentals
A network is a graph (consists of nodes and edges)
L1
L2
Examples:
Zina
Petrushyna • People and interactions between them
L1
Ralf Klamma L2
• Websites and links
Teacher
• Cities and traffic connections
Edges are Teacher
• directed/undirected L3 L3
L4
L4
• multiple
• weighted/unweighted
Teacher
Lehrstuhl Informatik 5
Two nodes are neighbors or adjacent when one
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
edge exist between two given vertices
Teacher
SummerSchool-
June09-3

4. Fundamentals
A path is a set of connected edges
A length of a path is number of edges on the path
Zina A distance of a path is a sum of the weights of the edges
Petrushyna
on the path
A cycle is a path with repeated vertices
Ralf Klamma
A subgraph is a part of graph
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-4

5. Network Characteristics:
Degree centrality
Degree of a vertex:
number of incoming and outgoing edges
L1
Zina • in-degree L2
Petrushyna
Ralf Klamma • out-degree
Teacher
• Simplest centrality measure L3
• A measure in some sense
L4
shows the popularity of an actor
Teacher
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-5

6. Network Characteristics:
Closeness
How far a node is from the others?
Zina
Petrushyna
The closeness of the node i is defined as:
c(i ) ≡
Ralf Klamma
1
∑ j∈Nd (i , j )
Who are leaders?
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-6

7. Network Characteristics:
Shortest-path
Zina
Petrushyna
Ralf Klamma
News, rumor, fad, message – does it know the ideal route?
To get from one place to another more likely a message
wanders around more randomly, encountering who it will.
Certainly it is possible for information to flow between two
individuals via a third mutual acquaintance, even when the
Lehrstuhl Informatik 5
(Information Systems)
two individuals in question are themselves well acquainted
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-7

8. Network Characteristics:
Betweenness
Measure for the influence an actor can exert
The shortest-paths v(j, k) for each j, k and j≠k
the betweenness of node i is
Zina
Petrushyna
Ralf Klamma
vi ( j, k )
bi ≡ ∑
j ≠k v( j, k )
Who controls the flow of information?
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-8

9. Networ Measures
Closeness and Betweenness
Degree
Ego-centric measure defining a node community
Communication activity
Betweenness
Zina
Petrushyna
Measure of the extent to which a node lies on the
Community control
Ralf Klamma
paths between others
Closeness
Measure of how long it will take information to spread
Depedence, consideretely
from a given node to others in the network
efficiency
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-9

10. Examples
Zina
Petrushyna
Ralf Klamma
Lehrstuhl Informatik 5
(Information Systems)
Prof. Dr. M. Jarke
Joint TEL
SummerSchool-
June09-10