To add another ANS, click the New button, this will create another entry in the table that can be edited as required.

The Host field shows the I.P address (i.e. network location) of the machine that the ANS will run on, this defaults to the I.P address of the machine that is currently running the Generator tool.  More than one ANS can reside on a single host.

To change the location of the ANS double click on the Host field and enter the new value. If you don't know the I.P address of machine, use the ping command to discover it.

If there is more than one ANS the developer can choose which is the root server, the only operational difference of changing this is the root server will provide the time-grain value (see below) and be responsible for maintaining the society-wide clock.

To select or deselect an agent as the root, click on the 'Is Root?' field. Note: one ANS must be selected as the root.

The agent selected as the root will provide the time-grain value for the entire society, (for a discussion of the time-grain and its implications see section 3 of this document).   

Change the time-grain by double clicking the Time Grain field, the new value should be expressed in minutes and be a non-negative real number. For instance to set the time-grain to 20 seconds 0.33 should be entered.  Note: only the time grain field of the root ANS can be edited. 

As the root ANS serves as a reference point for all other agents in the society, there must be a means to inform other agents where the root ANS is located.  Hence when the root ANS starts, it will write its network location into a file called the Default Name Server (DNS) file.  If agents share a network file system it is recommended that the DNS file be expressed in terms of a network pathname.   

To edit the pathname to which the root ANS will write the DNS, double click on the Address File field of the root agent.

To make non-root name servers aware of the root ANS, they must be told where to find the root's DNS file.  This pathname is entered into the DNS File field.  If this is not a network accessible file, it will need to be copied to the local file system of the agent concerned, and hence this field will contain its local pathname and filename.

To edit the pathname from which the DNS file will be read, double click on the DNS File field of the root agent.

The developer can choose whether Agent Name Servers will be created with a graphical user interface, (GUI).  The GUI will display information on the server's activity, and provide some control functions.  This may be useful for debugging and monitoring, but unnecessary if the ANS is to run in the background.

To create an ANS with a GUI click the 'Create GUI?' checkbox field, click again to deselect.

UTIL-2: Configuring the Facilitators

Whereas every agent society must have an ANS, there is no such obligation for Facilitators.  Whether Facilitators are included depends on the nature of the application; if all agent acquaintances and abilities have been determined at design-time and will not change, then a Facilitator may not be necessary.  However, this situation is unlikely, and so most applications will possess at least one Facilitator, which can be created and configured using the 'Facilitators' panel, as shown in Figure 4.2.

Figure 4.2: The Facilitator Entry Panel

By default the Facilitators table has one entry, one should suffice for small-scale applications, but as it could be a potential bottleneck it may be desirable to have multiple Facilitators for larger applications, or where some redundancy is wanted in case of failure.

  To add another Facilitator, click the New button, this will create another entry in the table that can be edited as required.

The Host field shows the I.P address (i.e. network location) of the machine that the Facilitator will run on, this defaults to the I.P address of the machine that is currently running the Generator tool.  More than one Facilitator can reside on a single host.

To change the location of a Facilitator double click on the Host field and enter the new value. If you don't know the I.P address of machine, use the ping command to discover it.

To make Facilitators aware of the root ANS, they must be told where to find its DNS file.  This pathname is entered into the DNS File field.  If this is not a network accessible file, it will need to be copied to the Facilitator's local file system, and its local pathname and filename entered in this field.

To edit the pathname from which the DNS file will be read, double click on the DNS File field.

The developer can choose whether Facilitators will be created with a graphical user interface, (GUI).  The GUI will display information on the agent's activity, and provide some control functions.  This may be useful for debugging and monitoring, but unnecessary if the agent is to run in the background.

To create a Facilitator GUI click the 'Create GUI?' checkbox field, click again to deselect.

How to Make the Facilitator Reactive

The normal behaviour of a Facilitator is to retrieve the list of known agents from an ANS, and then send a message to each of the agents asking them to reply with details of the abilities they are currently able to perform.  The interval between these queries is set through the Recycle Period field.

Change the cycle interval by double clicking the Recycle Period field, the new value should be expressed in minutes and be a non-negative real number. 

If the cycle period is set to 0 the Facilitator will cease its proactive querying of agents and become totally reactive.  In this case the normal roles are reversed and the agents must behave proactively, periodically advertising their abilities to the Facilitator.  This will require altering the agent's normal behaviour, (see How to Instruct an Agent to Do Something).

UTIL-3: Configuring the Visualisers

Like Facilitators, there is no requirement for an application to contain a Visualiser. Whether one is included depends on whether the application is to be debugged, monitored or analysed.  Given the Visualiser offers some very useful functionality for free it will usually be included in the list of agents to be created.  Visualisers are created and configured using the 'Visualisers' panel, shown in Figure 4.3.

Figure 4.3: The Visualiser Entry Panel

By default the Visualisers table has one entry, whether more than one is necessary will probably depend on the number of locations where users will want to visualise some aspect of the society. Another influencing factor is that Visualisers are not essential to the operation of an agent society, and so as the implications of failure are less serious there is less need for redundancy.

  To add another Visualiser, click the New button, this will create another entry in the table that can be edited as required.

The Host field shows the I.P address (i.e. network location) of the machine that the Visualiser will run on, this defaults to the I.P address of the machine that is currently running the Generator tool.  As the Visualiser windows will occupy most of a host's screen space, there is likely to be only one Visualiser per host (although this is not enforced).

To change the location of a Visualiser double click on the Host field and enter the new value. If you don't know the I.P address of machine, use the ping command to discover it.

To make Visualisers aware of the root ANS, they must be told where to find its DNS file.  This pathname is entered into the DNS File field.  If this is not a network accessible file, it will need to be copied to the Visualiser's local file system, and its local pathname and filename entered in this field.

To edit the pathname from which the DNS file will be read, double click on the DNS File field.

The developer can choose whether Visualisers will be created with a GUI that will display information on the Visualiser agent's activity; (this will be created separately from the windows of the Visualiser tools). This GUI may be useful for debugging and understanding how the agent works, but otherwise this option should be ignored.

To create a Visualiser with an activity GUI click the 'Create GUI?' checkbox field; click again to deselect.

UTIL-4: Configuring the Database Proxies

A Database Proxy (DP) agent provides Visualiser agents with a means of persistent storing agent session information.  A DP can serve as an interface to a 3^rd party database, or translate the information to be stored into its own ASCII file format.  Database Proxies are created and configured through the panel of the same name, shown in Figure 4.4, although there is no entry there by default.

Figure 4.4: The Database Proxy Entry Panel

Whether a DP is included in an application depends on whether the activities of the agents need to be logged.  Hence a DP will typically only be created if the society is being debugged or audited, and a DP will not be created by default.

  To add a Database Proxy, click the New button, this will create an entry in the table that can be edited as required.

The Host field shows the I.P address (i.e. network location) of the machine that the Database Proxy will run on, this defaults to the I.P address of the machine that is currently running the Generator tool.  If the DP is to be connected to a proprietary database the address entered will probably need to be the address of the machine that hosts the database.

To change the location of the DP double click on the Host field and enter the new value. If you don't know the I.P address of machine, use the ping command to discover it.

Like the other utility agents the DPs must be aware of the root ANS.  Thus the location of the DNS file should be entered into the DNS File field.  If this is not a network accessible file, it will need to be copied to the DP's local file system.

To edit the pathname from which the DNS file will be read, double click on the DNS File field.

The developer can choose whether the DP will be created with a GUI that will display information on its activities. This GUI may be useful for debugging and understanding how the agent works, but otherwise this option should be ignored.

To create an activity GUI click the 'Create GUI?' checkbox field; click again to deselect.

How to Connect a Database Proxy to a Storage Medium

The Database Proxy is connected to its storage media through a Java class that implements the methods of the storage interface.  The ZEUS toolkit provides two predefined storage interfaces:

1. zeus.ext.FlatFile : this writes saved information into a conventional ASCII file

2. zeus.ext.Oracle : this writes information into an Oracle Database using a ODBC connection

To choose the storage mechanism to be used, double click on the Proxy Classpath field and enter the full pathname of the appropriate class.  If this is not entered the DP will not be able to save information.