NETWORK Procedure

This example considers the terrorist communications network from the attacks on the United States on September 11, 2001, described in Krebs (2002). Figure 219 shows this network, which was constructed after the attacks, based on collected intelligence information.

Figure 219: Terrorist Communications Network from 9/11

The full network data include 153 links. The following statements show a small subset to illustrate the use of the BICONNECTEDCOMPONENTS statement in this context:

data mylib.LinkSetInTerror911;
   input from & $32. to & $32.;
   datalines;
Abu Zubeida                Djamal Beghal
Jean-Marc Grandvisir       Djamal Beghal
Nizar Trabelsi             Djamal Beghal
Abu Walid                  Djamal Beghal
Abu Qatada                 Djamal Beghal
Zacarias Moussaoui         Djamal Beghal
Jerome Courtaillier        Djamal Beghal
Kamel Daoudi               Djamal Beghal
Abu Walid                  Kamel Daoudi
Abu Walid                  Abu Qatada
Kamel Daoudi               Zacarias Moussaoui
Kamel Daoudi               Jerome Courtaillier
Jerome Courtaillier        Zacarias Moussaoui
Jerome Courtaillier        David Courtaillier
Zacarias Moussaoui         David Courtaillier
Zacarias Moussaoui         Ahmed Ressam
Zacarias Moussaoui         Abu Qatada
Zacarias Moussaoui         Ramzi Bin al-Shibh
Zacarias Moussaoui         Mahamed Atta
Ahmed Ressam               Haydar Abu Doha
Mehdi Khammoun             Haydar Abu Doha
Essid Sami Ben Khemais     Haydar Abu Doha
Mehdi Khammoun             Essid Sami Ben Khemais
Mehdi Khammoun             Mohamed Bensakhria
...
;

Suppose that this communications network had been discovered before the attack on 9/11. If the investigators’ goal was to disrupt the flow of communication between different groups within the organization, then they would want to focus on the people who are articulation points in the network.

To find the articulation points, use the following statements:

proc network
   links    = mylib.LinkSetInTerror911
   outNodes = mylib.NodeSetOut;
   biconnectedComponents;
run;

data mylib.ArtPoints;
   set   mylib.NodeSetOut;
   where artpoint=1;
run;

The output data table mylib.ArtPoints contains members of the network who are articulation points. By focusing on cutting off these particular members, investigators could have significantly disrupted the terrorists’ ability to communicate when planning the attack.