The Network Solver

This example considers the terrorist communications network from the attacks on the United States on September 11, 2001, described in Krebs 2002. Figure 9.78 shows this network, which was constructed after the attacks, based on collected intelligence information.

Figure 9.78: 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 BICONCOMP option in this context:

data 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

   ... more lines ...   

Nawaf Alhazmi              Khalid Al-Mihdhar
Osama Awadallah            Khalid Al-Mihdhar
Abdussattar Shaikh         Khalid Al-Mihdhar
Abdussattar Shaikh         Osama Awadallah
;

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 optmodel;
   set<str,str> LINKS;
   read data LinkSetInTerror911 into LINKS=[from to];
   set NODES = union{<i,j> in LINKS} {i,j};
   set<str> ARTPOINTS;

   solve with NETWORK /
      links     = (include=LINKS)
      biconcomp
      out       = (artpoints=ARTPOINTS)
   ;

   put ARTPOINTS;
   create data ArtPoints from [node]=ARTPOINTS artpoint=1;
quit;

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.