Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

17.3.2 Implementation of Production Rules in a Knowledge-Based System

Intended learning outcomes: Differentiate between the representation of the bill of material or routing sheet for a product with options and the standard version without variants. Explain the extended primary key for a bill of material with options.

The following structure with three objects illustrates a production rule using object classes (see Sections 17.2.1, 17.2.3, 17.2.6, and 17.2.8):

  1. The conventional item business object for items and item families, for products and components.
  2. The bill-of-material position variant or operation variant. This is the conventional object bill-of-material position or operation, plus a variant number, which also belongs to the bill-of-material position ID or operation ID.
    The assembly has, for example, u positions, where u >= 1. For each position x, 1 <= x <= u, there are thus vx variants, vx >= 1. If there is only one variant, then there is equality; this is the conventional situation with an unconditional bill of material.
  3. The IF clause. This is a logical expression in parameters such as “type,” “length,” and so forth.

The three objects — product family, position variant, and IF clause — are linked together to form a production rule.

  • “If product (a) and IF clause (c) are true, then the position variant (b) applies in the bill of material or
    routing sheet. In the case of the bill of material, it is thus true (or “is inferred”) that the component in (b) is a (new) fact.”

If analysis of the rule “infers” a component and thus adds to the fact bank, and this compo­nent is an intermediate product, then a further pass of the inference engine activates all the rules, and processes those that are assigned to the intermediate product (a). Such forward chain­ing corres­ponds to the processing of a multilevel bill of material (see Section 17.2.3).

The structure shown below is an extension of the traditional bill of material and routing sheet. The generalized structure and special case often encountered in the past are shown in graphical form in Figure for ease of understanding. If we select vx = 1 and no clause for all x, 1 <= x <= u, then we obtain the con­ventional case of the “unconditional” bill of material or routing-sheet position.

Fig.       Representation of the bill of material or routing sheet for a product with options (thick lines: standard version without variants).

Figure shows this extension by supplementing the primary key of the conventional bill-of-material position object with the variant number. The simplest version of the IF clause is a succession of simple logical expressions; for example, connections such as type = 2 and order quantity > 100, linked with “and” or “or” in the manner of the disjunctive or conjunctive normal form. See also [Schö88a], p. 49 ff. For more complicated connections, it is better to use a formula scanner, which will create the logical expression in free form using the rules of Boolean algebra. In cases where the clauses are not self-explana­to­ry, text linked to a production rule may be used to store a declaration component, in addition to its true function as a means for the operation description.

Fig.          Extended primary key for a bill of material with options.

Reference is made to Figure, to demonstrate the way the inference engine works. It keeps the variants within a position in the best order for the query by counting the variants selected in previous queries and periodically rearranging these variants, sorting them by frequency of occurrence. For his part, the expert selects a criterion, for example, a lexico­graphical criterion, suitable for administering and arranging the variants.

Course section 17.3: Subsections and their intended learning outcomes