CLIPS中嵌套多槽字段建模现实工件的技术问题咨询

背景 #

我正在对现实工件建模，使用CLIPS 6.4处理包含嵌套流程信息的系统推理，但在将深度嵌套的C++数据结构映射到CLIPS数据类型时遇到了困难。

C++数据结构示例 #

struct Vehicle {
    enum Category category;
    std::list<Engine> engines;
    std::list<Wheel> wheels;
    std::list<Instrument> instruments;
};

struct ORing {
    enum metal_type;
    bool has_seal;
    float diameter;
    float length;
    float weight;
};

struct Piston {
    int foo;
    float foobar; 
    std::string foofoo;
    std::list<ORing> orings;
};

struct Engine {
    std::list<Piston> piston;
    float weight;
};

struct Wheel {
  float diameter;
  bool has_alloy;    
};

struct Widget {
    std::string name;
};

struct Instrument {
    std::string name;
    bool is_electronic;
    std::list<Widget> widgets;
};

对应的CLIPS数据类型定义 #

(deftemplate vehicle
   (slot category (type SYMBOL) (allowed-symbols CAR BUS TRUCK TRAIN SHIP AIRCRAFT))
   (multislot engines (type SYMBOL))
   (multislot wheels (type SYMBOL))
   (multislot instruments (type SYMBOL))
)

(deftemplate engine
    (multislot pistons (type SYMBOL))
    (slot weight (type FLOAT) (range 0.01 ?VARIABLE) )
)

(deftemplate wheel
    (slot diameter (type FLOAT) (range 0.01 ?VARIABLE) )
    (slot has_alloy (type SYMBOL) (allowed-symbols YES NO) )
)

(deftemplate widget
    (slot name (type STRING))
)

(deftemplate instrument
    (slot name (type STRING))
    (slot is_electronic  (type SYMBOL) (allowed-symbols YES NO) )
    (multislot widget (type SYMBOL))
)

问题解答 #

1. 如何断言一个所有槽位均填充完成的vehicle事实？ #

需要先断言嵌套的子事实（如engine、wheel、instrument等），再将这些子事实的引用（通常是事实索引或自定义标识符）填入vehicle的多槽中。示例如下：

; 先断言子事实
(assert (widget (name "fuel-sensor-widget")))
(assert (instrument (name "fuel-gauge") (is_electronic YES) (widget 1))) ; 1是widget事实的索引

(assert (wheel (diameter 18.5) (has_alloy YES)))

(assert (engine (weight 250.0) (pistons 2))) ; 假设2是已断言的piston事实索引

; 最后断言vehicle事实，引用子事实的索引
(assert (vehicle (category CAR) (engines 3) (wheels 2) (instruments 1)))

注：CLIPS中事实被断言后会自动获得唯一索引，也可以用gen-id生成自定义标识符来关联子事实。

2. 如何获取多槽字段并检查其中条目数量？ #

可以用$?匹配多槽，结合length$函数获取条目数量。示例：

(defrule count-vehicle-engines
   (vehicle (category ?cat) (engines $?engine-list))
   =>
   (printout t "Vehicle of category " ?cat " has " (length$ ?engine-list) " engines." crlf)
)

length$ ?engine-list会返回多槽中元素的个数。

3. 如何从多槽字段中获取第i个元素？ #

CLIPS中多槽的元素索引从1开始，用nth$函数获取指定位置的元素。示例：

(defrule get-second-engine
   (vehicle (engines $?engine-list))
   =>
   (if (> (length$ ?engine-list) 1)
      then
      (bind ?second-engine (nth$ 2 ?engine-list))
      (printout t "Second engine's fact index: " ?second-engine crlf)
   )
)

nth$ 2 ?engine-list会返回多槽中第2个元素。

4. 如何从多槽字段的第i个元素中获取指定字段？ #

需要先通过索引获取子事实的引用，再用fact-slot-value函数提取子事实的槽值。以获取第2个引擎中第2个ORing的metal_type为例：

; 首先补充缺失的piston和oring模板
(deftemplate piston
    (slot foo (type INTEGER))
    (slot foobar (type FLOAT))
    (slot foofoo (type STRING))
    (multislot orings (type SYMBOL))
)

(deftemplate oring
    (slot metal_type (type SYMBOL))
    (slot has_seal (type SYMBOL) (allowed-symbols YES NO))
    (slot diameter (type FLOAT))
    (slot length (type FLOAT))
    (slot weight (type FLOAT))
)

(defrule get-oring-metal-type
   (vehicle (engines $?engine-list))
   =>
   ; 先获取第2个引擎的ID
   (bind ?second-engine-id (nth$ 2 ?engine-list))
   ; 获取该引擎的第2个piston ID
   (bind ?second-piston-id (nth$ 2 (fact-slot-value ?second-engine-id pistons)))
   ; 获取该piston的第2个oring ID
   (bind ?second-oring-id (nth$ 2 (fact-slot-value ?second-piston-id orings)))
   ; 提取该oring的metal_type
   (bind ?metal-type (fact-slot-value ?second-oring-id metal_type))
   (printout t "Second engine's second ORing metal type: " ?metal-type crlf)
)

5. 如何向多槽字段添加/移除条目？ #

使用modify命令结合多槽操作符来更新已断言的事实：

添加条目

(defrule add-third-engine
   (vehicle (fact-index ?vid) (engines $?engine-list))
   (engine (fact-index ?eid)) ; 要添加的新引擎事实
   =>
   ; 在engines多槽末尾添加新引擎ID
   (modify ?vid (engines ?engine-list ?eid))
)

移除条目

通过模式匹配定位并移除：

(defrule remove-third-engine
   (vehicle (fact-index ?vid) (engines $?pre [?third-engine] $?post))
   =>
   ; 移除第3个引擎
   (modify ?vid (engines ?pre ?post))
)

通过索引定位移除：

(defrule remove-engine-by-index
   (vehicle (fact-index ?vid) (engines $?engine-list))
   =>
   (if (> (length$ ?engine-list) 2)
      then
      ; 移除第3个元素，拼接前后部分
      (bind ?new-list (create$ (nth$ 1 2 ?engine-list) (nth$ 4 (length$ ?engine-list) ?engine-list)))
      (modify ?vid (engines ?new-list))
   )
)

内容的提问来源于stack exchange，提问作者Homunculus Reticulli