The need for a chemical/biological early warning system within mass transportation sites is real and was being researched before the September 11 terrorist attacks. Since then, this research has become an operational necessity.
Led by Argonne National Laboratory, along with teams from Sandia National Laboratories (SNL) and Lawrence Livermore National Laboratory (LLNL), researchers created an early warning system for subways within a major metropolitan area. The entire system entailed the processing of sensor data, live meteorological data, video feeds, and real-time track/train data; execution of below- and aboveground dispersion models; and the timely display of results to subway and emergency personnel. The system is based extensively on Java technologies, and this article examines the merits of each J2EE package used.
The Chem-Bio Emergency Management Information System (CB-EMIS) is an enterprise-level distributed system. The decision to write it in Java was made early because of Java's maturity, scalability, and maintainability, as well as the availability of the industry-supported J2EE technologies. This article discusses the software aspects of the CB-EMIS and presents the architecture in detail.
Industry Standard Technologies
The CB-EMIS runs on four dual-processor Dell PCs running the Red Hat 8 Linux Operating System (the servers). Because the system must always be up and able to recover from communication failures, etc., three J2EE technologies were used to gain this reliability: Java Messaging Service (JMS), Remote Method Invocation Object Activation Daemon (RMID), and persistence through Java Database Connectivity (JDBC). A relational database was used to persist data for forensic playback and simulation modes (MySQL for development and training, and Oracle 9i for operational use).
The Sun ONE (previously iPlanet) Message Broker was used for the JMS system, and Novell's Lightweight Directory Access Protocol (LDAP) implementation (eDirectory) was set up for use as the directory service and for the authentication of users. It's important that the server processes across all CPUs remain synchronized in time; a Network Time Protocol (NTP) server was used to keep the system times in sync. Since the system relied on JMS messages, it was important to have the times match for message time-out purposes. Also, the Time Server process reads the system time to keep a consistent time stamp for all data and messages passing through the other server processes.
CB-EMIS System-Level Services
This section describes the design of the foundational services layer with which all server processes extend, implement, or interface. Figure 1 shows the services layer that supports the CB-EMIS.
Directory Service
The LDAP server was used for authentication of user accounts as well as a directory service for object binding. The schema was also extended to allow the storage of attributes unique to the system on a per-user basis, allowing control over what each user could see or do in the client graphical user interface (GUI). The Java Naming and Directory Interface (JNDI) package was used throughout the CB-EMIS to bind and look up object references stored in the LDAP server. Figure 2 shows the various objects bound into the directory. Not only were the JMS Topics and Topic Connection Factory references bound in the server, but the various JDBC data sources were as well. In this way, any of the CB-EMIS processes can look up the references to all the connection factories, topics, and JDBC data sources without having provider-specific references within the code. Saving these objects within an LDAP server gains persistence and security, and avoids the need for a shared file system. The team also decided to bind the CB-EMIS server process Remote Method Invocation (RMI) stub references within the LDAP server. Because there's not a JNDI class for binding stub references within a directory server, it was necessary to write our own javax.naming.spi.ObjectFactory and javax.naming.Referenceable classes to serialize/deserialize the java.rmi.server.RemoteStubs.
