Deftemplate and Single-slot or multislot in AI

Deftemplate

Deftemplate is similar to a struct definition in C. That is, the deftemplate defines a group of related fields in a pattern similar to the way in which a C struct is a group of related data.

A deftemplate is a list of named fields called slots. Deftemplate allows access by name rather than by specifying the order of fields.

Deftemplate contributes to good style in expert systems programs and is a valuable tool of software engineering.

Single-slot

A slot is a named single-slot or multislot. A single-slot or simply slot contains exactly one field while a multislot contains zero or more fields.

Any number of single or multislot may be used in a deftemplate. To write a slot, give the field name (attribute) followed by the field value.

Note that a multislot slot with one value is strictly not the same as a single-slot. As an analogy, think of a cupboard (the multislot) that may contain dishes.

A cupboard with one dish is not the same as a dish (single-slot.)

However, the value of a single-slot slot (or variable) may match a multislot slot (or multislot variable) that has one field.

As an example of a deftemplate relation, consider the attributes of a business who might be considered good for prospect.

   Attributes Value
   name "Dopey Wonderful"
   assets rich
   age 99

(deftemplate prospect ; name of deftemplate relation
"vital information" ; optional comment in quates
(slot name                               ; name of field
     (type STRING)                  ; default value of field name
     (default ?DERIVE) )         ; default value of field name
(slot assets                               ; name of field
     (type SYMBOL)                ; type of field
     (default rich))                     ; default value of field assets
(slot age                                   ; name of field

(type NUMBER) ; type. NUMBER can be INTEGER or FLOT

(default 80))) ; default value of field age

In this example, the components of deftemplate are structured as:

A deftemplate relation name
Attributes called fields
The field type, which can be any one of the allowed types: SYMBOL, STRING, NUMBER, and others.
The default for the field value

(assert (prospect))
As you see, CLIPS has inserted the default value of the null string, ''', for the name field since that is the default for a STRING. Likewise, the asserts and age defaults were also inserted by CLIPS. Different types have different default symbols such as the null string, " ", for STRING; the integer 0 for INTEGER; the float 0.0 for FLOT and so on.
The ?DRIVE keyword select the appropriate type of constraints for that slot, e.g., the null string, " ", for a slot of type STRING.

   (defrule business-candidate
   (prospect (name ?name) (assets ?net_worth)
(age ?months) )
      =>
(printout t "Prospect: " ?name crlf
   ?net_worth crlf ?months " months old" crlf) )