The OPTNET Procedure

This example considers the terrorist communications network from the attacks on the U.S. on September 11, 2001, described in Krebs 2002. Output 2.1.1 shows this network, which was constructed after the attacks, based on collected intelligence information. The image was created using SAS/GRAPH^® Network Visualization Workshop 2.1 (see the SAS/GRAPH: Network Visualization Workshop User's Guide).

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

data LinkSetInTerror911;
   length from $25 to $32;
   input from to;
   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 optnet
   data_links = LinkSetInTerror911
   out_nodes  = NodeSetOut;
   biconcomp;
run;

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

The data set ArtPoints contains members of the network who are articulation points. Focusing investigations on cutting off these particular members could have caused a great deal of disruption in the terrorists’ ability to communicate when formulating the attack.