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Oracle Database HOWTO Paul Haigh, paul@nailed.demon.co.uk v1.0, 10 March 1998 A guide to installing and configuring the Oracle Database Server on a Linux system 1. Introduction 1.1. Version History ╖ v0.1 - 21 Feb 1998 - Paul Haigh - Original Version ╖ v0.2 - 01 Mar 1998 - Paul Haigh - Comments From Proofreaders Added ╖ v1.0 - 10 Mar 1998 - Paul Haigh - Released to LDP 1.2. Copyright The Oracle Database HOWTO copyright (c) 1998, Paul Haigh. Like all Linux HOWTO documents, this may be reproduced and distributed in whole or in part, in any medium, physical or electronic, so long as this copyright notice is retained on all copies. Commercial redistribution is allowed and encouraged; however the author would like to be notified of such distributions. You may translate this HOWTO into any language whatsoever provided that you leave this copyright statement and disclaimer intact, and that you append a notice stating who translated the document. 1.3. Disclaimer While I have tried to include the most correct and up to date information available to me, I cannot guarantee that usage of information in this document does not result in loss of data or equipment. I provide NO WARRANTY about the information in the HOWTO and I cannot be made liable for any consequences resulting from using the information in this HOWTO. 1.4. Aim of the HOWTO In this HOWTO I will attempt to cover installation and basic admin of an Oracle database running on a Linux machine. In particular I will cover Oracle server installation, SQL*Net configuration and client configuration. This document is not an in depth tutorial on using or administering an Oracle database, if that is what you are looking for there are great books on those subjects published by O'Reilly and others. I am also not going to cover the development of Oracle programs under UNIX. If this is absolutley necessary to you then I would recommend that you purchase the SCO development system (with OpenServer 5.x) from SCO, which I am told can be obtained for a very reasonable US $19, from www.sco.com. 1.5. Requirements I am assuming a number of items that you will need for following the HOWTO. ╖ Oracle Server CD for SCO Openserver (Version 7.3.3.0.0.) This must be a legal copy. Remember that Oracle are a profit making company and charge for their products. If you want a free SQL compliant database use PostgresSQL or similar. It is also possible to install oracle, using a 60 day evaluation licence, from a downloadable tar file from the Oracle web site. I have not personally tried this and it is completely unverified. ╖ A Linux Server You wouldn't be reading this without one...would you? ╖ Kernel 2.0.30+ I cannot guarantee that these instructions will be accurate for any other Kernel. (Not that I am guaranteeing it for 2.0.30 either...). ╖ iBCS It is very important to have this installed and working with the latest possible version for your platform. (I am using iBCS-2.0-10.i386.rpm from Redhat Linux). ╖ Lots of disc space 600 Mb+ is a reasonable amount. It is possible to install with less but you need to make some sacrifices, and I never like starting with those. However, I will attempt to point out areas in which space can be freed up. ╖ 32Mb+ Ram I know that this sounds like a lot, especially in Linux terms, but remember that Oracle is a complex piece of software. You wouldn't have the same reservations on SCO! I am not saying that Oracle doesn't work with less, just that it is less than Oracle recommend and I wouldn't suggest it. ╖ Licenses from Oracle I know that I have already mentioned this but I want to be clear that this is important. Using software from Oracle without a license is illegal. 1.6. Future Improvements Here are the areas of the Oracle server that are not covered in this HOWTO. However, time permitting, I will attempt to get them into later versions of the HOWTO. ╖ Development of Oracle Pro* programs using the Oracle libraries. ╖ Installing different versions of Oracle server. ╖ Installing Oracle Web Server. ╖ How to relink the Oracle Kernel. 2. Installing the Oracle Software 2.1. Server Preparation 2.1.1. Creating an Oracle User Unsurprisingly we require a user to hold the Oracle database. Since we have no desire to relink the Oracle kernel (more about that later) we have to accept the Oracle defaults for user name and group name. This includes the user ORACLE and the group DBA. 1. Login as Root 2. Create the oracle user and the group dba. ______________________________________________________________________ $ groupadd dba $ useradd oracle ______________________________________________________________________ 3. Ensure a home directory is created for the user oracle. ______________________________________________________________________ $ mkdir /home/oracle $ mkdir /home/oracle/7.3.3.0.0 (Version of Oracle) $ chown -R oracle.dba /home/oracle ______________________________________________________________________ 2.2. Installing from CDROM Unfortunately the Oracle Installer on the SCO disc will not work. A variety of problems can be experienced, from core dumps to hangs. As a result we need to copy the files from the CDROM manually and uncompress them: (Ensure the CDROM is mounted on the system). 1. Log on as Oracle 2. Change directory to /home/oracle/7.3.3.0.0. 3. Copy all install files from CDROM ______________________________________________________________________ $ cp -a /mnt/cdrom/* . ______________________________________________________________________ 4. Un-compress all Oracle files on CDROM. ______________________________________________________________________ $ find . -name *_ -exec ~/7.3.3.0.0/orainst/oiuncomp {} \; ______________________________________________________________________ 2.3. Post Installation Tasks 2.3.1. Tasks for Root Add the following lines to /etc/profile or add to the .profile for each user who is going to use Oracle. ______________________________________________________________________ # Oracle Specific ORACLE_HOME=/home/oracle/7.3.3.0.0 ORACLE_SID=orcl ORACLE_TERM=vt100 export ORACLE_HOME ORACLE_SID ORACLE_TERM # Alter path for Oracle PATH="$PATH:$ORACLE_HOME/bin" ______________________________________________________________________ We also need to change the owner and permissions of the Oracle ulimit increase utility. ______________________________________________________________________ $ chown root.root $ORACLE_HOME/bin/osh $ chmod u+s $ORACLE_HOME/bin/osh ______________________________________________________________________ 2.3.2. Tasks for Oracle Change permissions for the Oracle files to ensure correct operation. ______________________________________________________________________ $ chmod +x $ORACLE_HOME/bin/* $ chmod u+s $ORACLE_HOME/bin/oracle ______________________________________________________________________ Oracle tools require the messages to be in the $ORACLE_HOME/tool_name/mesg directory. So, move the msb files from the msg_ship directories to the mesg directories. ______________________________________________________________________ $ mv $ORACLE_HOME/plsql/mesg/mesg_ship/* $ORACLE_HOME/plsql/mesg/. $ mv $ORACLE_HOME/rdbms/mesg/mesg_ship/* $ORACLE_HOME/rdbms/mesg/. $ mv $ORACLE_HOME/svrmgr/mesg/mesg_ship/* $ORACLE_HOME/svrmgr/mesg/. ______________________________________________________________________ Create the following directories if they do not exist: ______________________________________________________________________ $ mkdir $ORACLE_HOME/rdbms/log $ mkdir $ORACLE_HOME/rdbms/audit $ mkdir $ORACLE_HOME/network/log ______________________________________________________________________ 2.3.3. Things you can remove The following directories can safely be removed: ╖ $ORACLE_HOME/guicommon2/ ╖ $ORACLE_HOME/ctx/ ╖ $ORACLE_HOME/md/ ╖ $ORACLE_HOME/mlx/ ╖ $ORACLE_HOME/precomp/ ╖ $ORACLE_HOME/slax/ 3. Creating a Database Now the Oracle server is installed we need to create a database to test the installation. 3.1. Create the Initialisation File Copy the $ORACLE_HOME/dbs/init.ora to $ORACLE_HOME/dbs/initorcl.ora: ______________________________________________________________________ $ cd $ORACLE_HOME/dbs $ cp init.ora initorcl.ora ______________________________________________________________________ Modify it by adding the following lines: ______________________________________________________________________ db_name = orcl COMPATIBLE=7.3.3.0.0 ______________________________________________________________________ 3.2. Creating the Database Install Script Create a script file called makedb.sql in the $ORACLE_HOME/dbs directory: ______________________________________________________________________ connect internal startup nomount set echo on spool makedb.log create database orcl maxinstances 1 maxlogfiles 8 datafile '$ORACLE_HOME/dbs/orcl_syst_01.dbf' size 40M reuse logfile '$ORACLE_HOME/dbs/orcl_redo_01.dbf' size 1M reuse, '$ORACLE_HOME/dbs/orcl_redo_02.dbf' size 1M reuse, '$ORACLE_HOME/dbs/orcl_redo_03.dbf' size 1M reuse; @$ORACLE_HOME/rdbms/admin/catalog.sql create tablespace rollback datafile '$ORACLE_HOME/dbs/orcl_roll_01.dbf' size 8.5M reuse; create tablespace temporary datafile '$ORACLE_HOME/dbs/orcl_temp_01.dbf' size 5M reuse temporary; create tablespace users datafile '$ORACLE_HOME/dbs/orcl_user_01.dbf' size 10M reuse; create rollback segment r1 tablespace rollback storage ( optimal 5M ); alter rollback segment r1 online; connect system/manager @$ORACLE_HOME/rdbms/admin/catdbsyn.sql connect internal @$ORACLE_HOME/rdbms/admin/catproc.sql connect system/manager @$ORACLE_HOME/sqlplus/admin/pupbld.sql spool off exit ______________________________________________________________________ 3.3. Running the Database Installation Script Start svrmgrl and run the script: ______________________________________________________________________ $ cd $ORACLE_HOME/dbs $ svrmgrl Oracle Server Manager Release 2.3.3.0.0 - Production Copyright (c) Oracle Corporation 1994, 1995. All rights reserved. Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production SVRMGR> connect internal Connected. SVRMGR> startup nomount ORACLE instance started. Total System Global Area 4313312 bytes Fixed Size 41876 bytes Variable Size 4140364 bytes Database Buffers 122880 bytes Redo Buffers 8192 bytes SVRMGR> @makedb <loads of messages> SVRMGR> exit Server Manager complete. ______________________________________________________________________ 3.4. Starting the Database Firstly, we need to bring up the database by hand (we will automate this later on). To startup an Oracle database we need to issue the startup command when connected internally: ______________________________________________________________________ $ svrmgrl Oracle Server Manager Release 2.3.3.0.0 - Production Copyright (c) Oracle Corporation 1994, 1995. All rights reserved. Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production SVRMGR> connect internal Connected. SVRMGR> startup ORACLE instance started. Total System Global Area 4313316 bytes Fixed Size 41876 bytes Variable Size 4140368 bytes Database Buffers 122880 bytes Redo Buffers 8192 bytes Database mounted. Database opened. SVRMGR> exit Server Manager complete. ______________________________________________________________________ 3.5. Stopping the Database It is worth mentioning here that restarting a Linux server without shutting down the Oracle database first there is a high risk of corrupting the database. So, before we issue the Linux shutdown command it is wise to bring down the database: ______________________________________________________________________ $ svrmgrl Oracle Server Manager Release 2.3.3.0.0 - Production Copyright (c) Oracle Corporation 1994, 1995. All rights reserved. Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production SVRMGR> connect internal Connected. SVRMGR> shutdown Database closed. Database dismounted. ORACLE instance shut down. SVRMGR> exit Server Manager complete. ______________________________________________________________________ 3.6. Create a Default User The database, as created, has a two special users which are automatically created. These are: ______________________________________________________________________ Username Password SYSTEM MANAGER SYS change_on_install ______________________________________________________________________ These users are typically used to hold the standard data dictionary information for the database. It is a good idea to change the passwords from the defaults as soon as possible. This can be achieved by: ______________________________________________________________________ sqlplus system/manager SQL*Plus: Release 3.3.3.0.0 - Production on Sat Feb 21 12:43:33 1998 Copyright (c) Oracle Corporation 1979, 1996. All rights reserved. Connected to: Oracle7 Server Release 7.3.3.0.0 - Production Release SQL> alter user system identified by <newpassword>; User altered. SQL> alter user sys identified by <newpassword>; User altered. SQL> exit; Disconnected from Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production ______________________________________________________________________ Since the user system/manager is similar to using root on a UNIX machine, we need to create a user with less ability to cause damage. (remember to bring up the database before attempting to create a user) Connect to SQL*Plus and create a user: ______________________________________________________________________ $ sqlplus system/manager SQL*Plus: Release 3.3.3.0.0 - Production on Sat Feb 21 12:43:33 1998 Copyright (c) Oracle Corporation 1979, 1996. All rights reserved. Connected to: Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production SQL> create user <user> identified by <psw> 2 default tablespace users 3 temporary tablespace temp; User created. SQL> grant connect, resource to <user> Grant succeeded. SQL> exit Disconnected from Oracle7 Server Release 7.3.3.0.0 - Production Release PL/SQL Release 2.3.3.0.0 - Production ______________________________________________________________________ Now that you have a new user on the system you can play with the new system. To login to the Oracle database: ______________________________________________________________________ $ sqlplus <user>/<password> ______________________________________________________________________ If this completes with no error messages then you have a working Oracle database. If you never want to connect to this database from anywhere but this server then the job is complete, enjoy! If, however, like most people you want to configure the networking software so that you can connect from other machines, keep on reading. 4. Configuring SQL*Net on the Server All of these files configure the Oracle networking software (SQL*Net, aka Net8 for Oracle8). These files should all be created on the server in the $ORACLE_HOME/network/admin directory. 4.1. tnsnames.ora The TNSNAMES.ORA file identifies services available from the machine. On our instance here we will describe all databases that the server has mounted. For each database instance on your server add a section like below: ______________________________________________________________________ orcl.world = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (COMMUNITY = tcp.world) (PROTOCOL = TCP) (Host = <INSERT HOST NAME OF SERVER HERE> ) (Port = 1521) ) (ADDRESS = (COMMUNITY = tcp.world) (PROTOCOL = TCP) (Host = <INSERT HOST NAME OF SERVER HERE> ) (Port = 1526) ) ) (CONNECT_DATA = (SID = ORCL) ) ) ______________________________________________________________________ 4.2. listener.ora The listener.ora file contains the descriptions of the services that other machines are allowed to connect to and any configuration that is required for the server listener. It contains sections for the listener name, listener address, databases served by the listener and configuration parameters. Here is an example: ______________________________________________________________________ # Name of listener and addresses to listen on LISTENER = ( ADDRESS_LIST = (ADDRESS = (PROTOCOL=tcp) (HOST=<INSERT HOST>) (PORT=1521) (COMMUNITY=UK_SUP_TCPIP) ) (ADDRESS = (PROTOCOL=ipc) (KEY=700) (COMMUNITY=UK_SUP_TCPIP) ) ) # List of services served by this listener SID_LIST_LISTENER= (SID_LIST= (SID_DESC= (SID_NAME=orcl) (ORACLE_HOME=/home/oracle/7.3.3.0.0) ) ) # Start of configuration parameters. TRACE_LEVEL_LISTENER=OFF TRACE_FILE_LISTENER = "listener" LOG_FILE_LISTENER = "listener" CONNECT_TIMEOUT_LISTENER = 10 STOP_LISTENER = YES DBA_GROUP = dba ______________________________________________________________________ 4.3. sqlnet.ora The sqlnet.ora file contains configuration for the particular node of the network. This is independent of the number of databases or the number of listeners. The most important thing in this file is the Dead Connection Timeout configuration variable. Dead connection timeout checks every incoming process to a database instance and ensures that the client end of it is still responding. If the client (of whatever type) is not responding then the Oracle server shadow process is killed. This is very useful if you have many clients accessing a database, especially during a developmental phase when those clients are more likely to be failing to exit cleanly from the Oracle database. Below is a copy of my own sqlnet.ora file for you to puruse: ______________________________________________________________________ TRACE_LEVEL_CLIENT = OFF sqlnet.expire_time = 30 # The number of seconds between client checks. names.default_domain = world name.default_zone = world ______________________________________________________________________ 4.4. Starting and Stopping the Listeners Now that the configuration of the listeners and SQL*Net is complete we can attempt to connect to the database using the networking software. (Before we were using direct links to the database, whereas here we are simulating a connection from a remote client machine). To start the listener using the above configuration: ______________________________________________________________________ $ lsnrctl LSNRCTL for SCO System V/386: Version 2.3.3.0.0 - Production on 23-FEB-98 20:38:25 Copyright (c) Oracle Corporation 1994. All rights reserved. Welcome to LSNRCTL, type "help" for information. LSNRCTL> start Starting /home/oracle/7.3.3.0.0/bin/tnslsnr: please wait... TNSLSNR for SCO System V/386: Version 2.3.3.0.0 - Production System parameter file is /home/oracle/7.3.3.0.0/network/admin/listener.ora Log messages written to /home/oracle/7.3.3.0.0/network/log/listener.log Listening on: (ADDRESS=(PROTOCOL=tcp)(DEV=6)(HOST=192.168.1.1)(PORT=1521)) Listening on: (ADDRESS=(PROTOCOL=ipc)(DEV=10)(KEY=700)) Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=magic.com)(PORT=1521)(COMMUNITY=UK_SUP_TCPIP)) STATUS of the LISTENER ------------------------ Alias LISTENER Version TNSLSNR for SCO System V/386: Version 2.3.3.0.0 - Production Start Date 23-FEB-98 20:38:50 Uptime 0 days 0 hr. 0 min. 0 sec Trace Level off Security OFF SNMP ON Listener Parameter File /home/oracle/7.3.3.0.0/network/admin/listener.ora Listener Log File /home/oracle/7.3.3.0.0/network/log/listener.log Services Summary... orcl has 1 service handler(s) The command completed successfully LSNRCTL> exit ______________________________________________________________________ To stop the listeners: ______________________________________________________________________ $ lsnrctl LSNRCTL for SCO System V/386: Version 2.3.3.0.0 - Production on 23-FEB-98 20:43:20 Copyright (c) Oracle Corporation 1994. All rights reserved. Welcome to LSNRCTL, type "help" for information. LSNRCTL> stop Connecting to (ADDRESS=(PROTOCOL=tcp)(HOST=magic.com)(PORT=1521)(COMMUNITY=UK_SUP_TCPIP)) The command completed successfully LSNRCTL> exit ______________________________________________________________________ If you have a DNS setup which doesn't return the IP address for the hostname specified then starting and stopping the listener can take some time (2-3 mins. dependant on the DNS timeout variable). If this is the case, don't worry, be patient. 5. Client Configuration 5.1. Windows Clients SQL*Net configuration on the PC using newer versions of the Oracle Client Software is very easy. The best (and easiest) way of achiving a fully working client installation is to use the SQL*Net Easy Configuration tool supplied by Oracle. This toolhas a wizard type interface to take you through the installation of the tnsnames.ora and sqlnet.ora files. Select "Add Database Alias" and enter a name for the alias when prompted. This alias is the name you will refer to the database instance as, and as such should be the same as the instance name (orcl in this case). Select TCP/IP as the protocol, and when prompted the hostname of the machine hosting the database and the instance name of the database. That's it. However, if you do not have the SQL*Net Easy Configuration Tool then don't worry. You can simply create the tnsnames.ora and the sqlnet.ora files in the $ORACLE_HOME/network/admin directory on the client exactly as they are on the server. This will provide an alias the same as on the server (always a good idea anyway). 5.2. Unix Clients UNIX clients are not very different that windows clients. If you have the Network Manager from Oracle then user that in the same way as above, if not then you can, again, just use the same configuration files as the server in the $ORACLE_HOME/network/admin directory. 6. Automatic Startup and Shutdown 6.1. dbstart & dbstop The automatic startup and shutdown of the Oracle database can be achieved (in 7.3.3.0.0) with the files dbstart and dbshut both provided by Oracle. These files rely on the existance of the file /etc/oratab to work (although by altering the dbshut and dbstart files this can be moved). The format of the /etc/oratab file is as follows: ______________________________________________________________________ SID:ORACLE_HOME:AUTO ______________________________________________________________________ An example: ______________________________________________________________________ orcl:/home/oracle/7.3.3.0.0:Y leaveup:/home/oracle/7.3.2.1.0:N ______________________________________________________________________ 6.2. init.d & rc.d To start and stop the database when the machine comes up and goes down by modifying the startup routines for the Linux machine. This is quite easy, although I should point out here that this may change depending on which flavour of Linux (slackware, debian, redhat, etc). I will show examples which work for Redhat Linux 5.0. To modify these for your own flavour of Linux, please see your Linux documentation sets. (Although it should hold true for any Sys V type UNIX). Firstly, we need to create the script which will run dbshut and dbstart in the /etc/rc.d/init.d directory. Create the following file as /etc/rc.d/init.d/oracle: ______________________________________________________________________ #!/bin/sh # # /etc/rc.d/init.d/oracle # Description: Starts and stops the Oracle database and listeners # See how we were called. case "$1" in start) echo -n "Starting Oracle Databases: " echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Starting Oracle Databases as part of system up." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle su - oracle -c dbstart >> /var/log/oracle echo "Done." echo -n "Starting Oracle Listeners: " su - oracle -c "lsnrctl start" >> /var/log/oracle echo "Done." echo "" echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Finished." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle touch /var/lock/subsys/oracle ;; stop) echo -n "Shutting Down Oracle Listeners: " echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Shutting Down Oracle Databases as part of system down." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle su - oracle -c "lsnrctl stop" >> /var/log/oracle echo "Done." rm -f /var/lock/subsys/oracle echo -n "Shutting Down Oracle Databases: " su - oracle -c dbshut >> /var/log/oracle echo "Done." echo "" echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Finished." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle ;; restart) echo -n "Restarting Oracle Databases: " echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Restarting Oracle Databases as part of system up." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle su - oracle -c dbstop >> /var/log/oracle su - oracle -c dbstart >> /var/log/oracle echo "Done." echo -n "Restarting Oracle Listeners: " su - oracle -c "lsnrctl stop" >> /var/log/oracle su - oracle -c "lsnrctl start" >> /var/log/oracle echo "Done." echo "" echo "----------------------------------------------------" >> /var/log/oracle date +"! %T %a %D : Finished." >> /var/log/oracle echo "----------------------------------------------------" >> /var/log/oracle touch /var/lock/subsys/oracle ;; *) echo "Usage: oracle {start|stop|restart}" exit 1 esac ______________________________________________________________________ It is worth checking that this file actually correctly stops and starts the databases for your system. Check the log file, /var/log/oracle for error messages. Once this script is working we need to create start and kill symbolic links in the appropriate runlevel directories /etc/rc.d/rcX.d. The following commands will ensure that the databases will come up in runlevels 2,3 and 4: ______________________________________________________________________ $ ln -s ../init.d/oracle /etc/rc.d/rc2.d/S99oracle $ ln -s ../init.d/oracle /etc/rc.d/rc3.d/S99oracle $ ln -s ../init.d/oracle /etc/rc.d/rc4.d/S99oracle ______________________________________________________________________ To stop the databases on reboot or restart we need the following links: ______________________________________________________________________ $ ln -s ../init.d/oracle /etc/rc.d/rc0.d/K01oracle # Halting $ ln -s ../init.d/oracle /etc/rc.d/rc6.d/K01oracle # Rebooting ______________________________________________________________________ 7. Other Bits 7.1. Intelligent Agent If you have a need for the Oracle Intelligent Agent, I found that you can run it without any configuration changes. To start the IA try: ______________________________________________________________________ $ lsnrctl dbsnmp_start ______________________________________________________________________ To stop the IA try: ______________________________________________________________________ $ lsnrctl dbsnmp_stop ______________________________________________________________________ There do not appear to be any messages indicating a sucessful or otherwise start or stop of the intelligent agent. However, the IA responded to Enterprise manager on the client side so I can only assume that it is working. 8. Credits This document was based on a document written by Bob Withers, bwit@pobox.com. Additional information taken from documents written by Georg Rehfeld, rehfeld@wmd.de and David Mansfield, david@claremont.com. Additional proof reading done by Bob Withers, Mark Watling, mwatling@mjw-ltd.demon.co.uk, Peter Sodhi, petersodhi@unn.unisys.com and Greg Hankins, greg.hankins@cc.gatech.edu. My thanks go to the tremendous support from all the people involved in this document and the research that has gone into it. Particular thanks to Bob Withers and Mark Watling for the additional comments and help they have provided.