Population of Profiles

The interaction described above should suffice for most users most of the time. However, the user also has complete access to the internal state of the agent and can modify any state variables governing the behavior of the agent. On the one hand, this involves more work to make the necessary changes. On the other hand, direct access provides a better understanding of the agent's behavior and greater control over it.

An agent is modeled as a population of competing profiles which compete for the user's attention by presenting articles. The population of profiles can be viewed by SHIFT-clicking (while the SHIFT key is pressed, click the mouse) on the appropriate Agent Icon. This brings up a window (Population Window) displaying the population of profiles that make up the agent (see figure ). This window allows access to the population level features of the system. The Population Window displays the population of profiles. Each icon (Profile Icon) represents the profile and the scale adjoining it indicates its fitness. The fitness of a profile can be modified by manipulating this scale.

There are a number of operators provided in the lower section of the window. These operators allow the user to manipulate the members of the population.

• A blank profile can be introduced into the population by using the ``Add'' operator. A blank profile must be initialized immediately (see Section ). This is because if no newsgroups are specified to be searched the profile would not be able to find any candidate articles. As a consequence, it would not receive feedback either.

• A member of the population can be eliminated by choosing the ``Kill'' operator.

• A ``mutated'' variant of a profile X can be added to the population by choosing operator ``Mutate'' and selecting profile X. Mutation modifies the set of newsgroups that a profile searches for articles. It does so by introducing a randomly selected newsgroup, similar to the newsgroup being replaced.

• Two profiles can be crossed over by exchanging some of the fields between them. This gives rise to two offspring profiles. This can be done by clicking the button labeled ``Xover'' and then selecting the two profiles to be crossed over.

• Instead of manipulating individual profiles, users can modify the whole population altogether. The next generation of the population is generated by retaining a certain number of the fit profiles, eliminating the rest and filling in the vacancies by genetic variants of the fit ones. This can be done by choosing the ``doNextGen'' operator.