Frame Based Network

When an agent encounters a new situation, it will need to retrieve information in order for it to act rationally in that situation. This information is likely to be multi-faceted and hierarchical, and one way of structuring the knowledge is in terms of frames. These are frameworks consisting of slots, with each slot containing information in various representations, including logical sentences and production rules. A slot can also contain another frame, which gives us a hierarchy.

Each framework represents a stereotypical object or situation and can be recalled whenever an agent encounters an object or situation which roughly fits the stereotype. After retrieving an appropriate frame, an agent will adapt it by changing some of the defaults, filling in blanks, etc. Some of the information is procedural, so that when a blank is filled in with certain values, a procedure must be carried out. Hence, not only will the frame provide a way of storing information about what is currently happening, it can also be used to dictate how to act rationally in that situation.

To make the frame representation as flexible as possible, different types of information are allowed in the slots. These include:

1. Information for choosing the frame. This might be a name, or id number. It may also be information about situations in which this frame should be retrieved, or some descriptors for the stereotype the frame represents. For example, a frame for a table might give some physical specifications and if a new object fits those specifications to a degree, then the frame should be retrieved.
2. Information about relationships between this frame and others, for example, whether this frame is a generalisation or specialisation of another frame, or whether two frames should never be considered at the same time.
3. Procedures which should be carried out after various slots have been filled in. These procedures could include: filling in particular values in other slots, retrieving other frames, or any rational action an agent should do in a situation where a particular value for a slot has been identified.
4. Default information. In situations where certain information required for the frame is missing, defaults can be specified. For instance, a table may be assumed to be wooden until this information can be ascertained. Default information is used in choosing actions until more specific information is found.
5. Blank slots. These are flagged to be left blank unless required for a particular task. For example, in a frame for lectures, the room of the lecture may be irrelevant for taking notes, but become important when planning how to get to lunch afterwards. 

As an example of using frames, suppose an agent is taking notes at a lecture and wants to decide how much attention to pay and determine any other ways in which it should behave. It searches for frames which match the given situation: it is in a meeting of some kind, so it retrieves that frame. In the specialisations slot of meetings is another frame, lecture, which is more appropriate because the context for that is a large number of students. It retrieves the lecture frame and starts filling in slots.

The first slot is the name of the course, which in this case is operating systems. The next slot is the level of the course, and it's difficult. This fires the procedural rule: "if it's a difficult course, pay attention", so the agent begins to pay more attention. The next slot is lecturer, and this is a frame in itself, so the agent retrieves the lecturer frame and starts filling in the slots on that frame. The first slot is tolerance, and this lecturer is not tolerant. This fires more procedural rules, such as "if it's an intolerant lecturer, then turn off your mobile phone", so the agent turns his phone off. Having dealt with the lecturer frame, it returns to the lecture frame and looks at the next slot, which is the room number. This is flagged to be not important for the task of taking notes, so the agent doesn't fill it in. The frames in this example are portrayed below:

We can see how this scheme of retrieving frames, filling in slots and reacting to production rules in the slots can be used to make an agent act rationally. Note that search may be involved in order to use the frames representation: both in order to find the correct frames for a situation, and as part of procedures carried out when filling the slots. 

Let us consider the another example ,

Frame description of Hotel room