Symbolic knowledge representation

Rather than trying to replace any of the above traditional techniques, this chapter presents the development of complementary frameworks and methodologies, supported by symbolic empirical machine learning algorithms (Kodratoff and Michalski, 1990 Shavlik and Dietterich, 1990 Shapiro and Frawley, 1991). These ideas from machine learning try to overcome some of the weaknesses of the traditional techniques in terms of both (1) the number and type of a priori decisions and assumptions that they require and (2) the knowledge representation formats they choose to express final solutions. 

With the view that a KBS interpreter is a method for mapping from input data in the form of intermediate symbolic state descriptions to labels of interest, four families of approaches are described here, each offering inference mechanisms and related knowledge representations that can be used to solve interpretation problems namely, model-based approaches, digraphs, fault trees, and tables. These methods have been heavily used... 

A Design Prototype is a knowledge representation schema which abstracts all requisite knowledge appropriate to that design situation (Gero 1990). Symbolically, a prototype proforma is expressed... 

The time evolution of the function f is thus replaced by a sequence of discrete symbols labeling the bins visited by each point of the orbit. Because of the coarse-graining of the phase space, however, detailed knowledge of the actual orbits is generally lost i.e. many different orbits may yield the same symbolic sequence. Different state-space partitionings also generally give rise to different symbolic representations. 

Even a simple representation such as this assumes a good deal of background knowledge in those expected to make sense of it. The representation combines graphical features meant to model the shape of the molecule, but includes symbols... 

Drawing on Background Knowledge to Interpret Symbolic Representations... 

One of the key messages of this chapter is that in chemistry we often nse representations that are potentially ambignons, bnt where the expert appreciates the intended symbolism by applying backgronnd knowledge according to contextnal ones. For example, the symbol d is commonly nsed in chemistry, bnt what does it represent If the context is bond , then the symbol has a rather different meaning to if the context is 3+ . 

The Pieknowledge Test was administered before using the teaching unit on chemical reactions. The Preknowledge Test consisted of three tasks with subtasks checking the stndents knowledge at the micro, submicro and symbolic types of representation, whereby the maximmn score obtainable was 27. Stndents spent 25 minutes in taking the test. Details of the tasks purposes and conceptions can be obtained from the anthors. 

Some tasks in the Test of Gained Knowledge required students to connect observations about the macro course of chemical reactions with their notations in the submicro and/or symbolic types of representation. The results indicate that most students were able to rearticulate the information about reactants and products of a chemical reaction from the textual description of chemical reaction into the form of word chemical equation (textual description of macros word equation of macro Task 8.2, f(o/ )=89.82% Task 9.1, f(o/ )=87.61%). This action corresponds to the first step in learning to write down chemical equation in the LON approach. It can easily be explained, because teachers described the learning process to be very efficient to this point, as is illustrated below ... 

This is the framework of methodologies that can be used to conduct legitimate enquiries in a subject, meaning those which lead to the production of acceptable scientific knowledge. The natures of each of the types within the representational triplet and their relationships to each other provide an explanatory framework in respect of all chemical phenomena. The macro and submicro types of representation do so for the Group A curriculum at the desired qualitative level, whilst the addition of the symbolic type completes the scope of chemical explanation in the Group B curriculum. 

Atoms and their symbols were introduced in Chap. 3 and 1. In this chapter, the representation of compounds by their formulas will be developed. The formula for a compound (Sec. 4.3) contains much information of use to the chemist. We will learn how to calculate the number of atoms of each element in a formula unit of a compound. Since atoms are so tiny, we will learn to use large groups of atoms—moles of atoms—to ease our calculations. We will learn to calculate the percent by mass of each element in the compound. We will learn how to calculate the simplest formula from percent composition data, and to calculate molecular formulas from simplest formulas and molecular weights. The procedure for writing formulas from names or from knowledge of the elements involved will be presented in Chaps. 5. ft. and 13. 

Understanding chemistry requires above all a knowledge of the language used. The preceding section introduced one of the basic shorthand systems used in chemistry the use of a symbol, usually one or two letters, to denote the elements. Symbols can be used in text as synonyms for the element, in discussion of nuclear structure as representation of a single atom of the element, or in equations as a fixed measure (such as the mole - see Section 2.3... 

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