Modeling a Knowledge Base

Modeling a knowledge base [CL02][RW02] contains several processes, construction,

maintenance, reuse and refinement. In the life cycle of KBS, KB maintenance and refinement repeat recurrently. In this section, the methodologies of modeling a knowledge base under NORM will be described.

4.4.1 Construction

The first process of modeling a knowledge base is construction, i.e., transforming the domain knowledge of experts into knowledge representation format of NORM. In this section, a construction procedure is proposed to construct the knowledge systematically. In knowledge base construction, it is assumed that no prior knowledge of the similar domain exists, and Extension-of relation will not be used in construction process. The construction procedure is divided into the following six steps.

1. Select a knowledge domain to be modeled

Before designing a knowledge base, the domain of the KB must be first selected. If a large system is built, the domain of the system may be divided into several sub-domains.

2. Identify concepts in the domain and model the concepts

This phase is to analyze what concepts are contained in one domain, similar to the use-case analysis in OOA/OOD. A concept in knowledge base is used to solve a problem as use-case.

In cognitive psychologist, the knowledge can be divided into three categories:

used to judge if the present facts correspond to things that the concept represents, and finally the result is obtained from the value of facts, e.g., deciding whether an entity is a bird according to the facts about its features.

Procedural knowledge contains the discrete steps or actions to be taken and the available alternatives to perform a given task. Thus a procedural concept is based on the visible facts to proceed planning for the concept, e.g., how to fix a bicycle. A plan may be generated from this kind of knowledge to solve a problem.

Strategic knowledge is used to decide course of action and regards the interrelationships and interdependencies among concepts. Strategic knowledge consists of reasoning strategy and control rules [KIN70]. In NORM, the control rules decide which KC will be used.

Figure 4.11 is an example to show the relations betweens the KCs containing one of the three types of knowledge. Procedural KC may acquire result inferring by other procedural or declarative KCs, or trigger a control KC. The Control KC can decide which KC will be used with existing facts. However, an inference process can start with any type of knowledge class.

Procedural

Figure 4.11: The cooperation of KCs with different types of knowledge

In this step, the type of concept to be modeled must be decided, and each concept must be mutual exclusive from each other.

3. Identify the relationships among concepts

Next, according to the exclusive relation of concepts, the type of their knowledge relation in NORM model must be found according to following basis. The concept with generalization is defined as Reference relation; the concept with causal relationship is defined as Trigger relation; at last, through further analysis, the sub problem or sub concept can be defined as Acquire relation.

4. Identify the features of each concept.

In this step, according to perception of experts, the features that affect each concept will be defined, and the facts in each concept will be used in designing corresponding KC.

Facts can be divided into two categories, respondent facts and required facts.

Respondent facts possess the function of output, which means all of the relevant

features generated through inferring the basic information, can be categorized as respondent facts. On the other hand, all necessary basic information for inferring with KC is a type of required facts.

5. Design the transformer

When a KB is constructed from several KCs, the transformer may be needed between KCs to transform useful facts. A transformer should be designed if the format requirements of cognominal feature facts between two KCs are different. The transformer will be assigned to the relation between KCs except Extension-of relation.

6. Acquire knowledge of each concept

Because rules are chosen to represent knowledge of each concept in NORM, the knowledge should be transformed into rule form. According to the relations between KCs analyzed in previous steps, this step acquires the knowledge of experts about each KC. The acquisition process for one KC can rely on some developed KA methodology such as repertory grid. However, the rules dealing with Trigger and Acquire relation between KCs should be asserted.

In order to avoid redundant design of the rules, the knowledge of a KC can be acquired if the KC is the top of relationship hierarchy between KCs, i.e., it does not refer other KCs.

4.4.2 Maintenance and Reuse

There are some differences between maintenance and reuse of existing knowledge in NORM. Maintenance means the modifier is the originator of a knowledge base system, but reuse means that someone else uses existing KC and modifies it.

Therefore, reusing an existing RB could be proceeded by building Extension-of relation.

Understanding an existing rule-base is the prerequisite to reuse or maintain it, which means user has to know the domain problem solved in the rule base, the concepts of KCs contained in the rule base, and the declarations of each fact in KCs. Thus, the process could be proceeded as follows.

1. Analyze the relationship of the new concept with original KCs.

In order to add a new concept to a rule-base, the relationships between new concept and original KCs must be known. In most cases, Reference is used to describe the relation between two KCs, which cooperates to solve a problem. Extension-of may be used if one KC is a modification of another KC and they have similar concept or solve the similar problem.

2. Identify the facts of the new KC.

According to the Extension-of or Reference relation, the key facts of new KC could be identified. In addition, the new concept may use features that are not declared in the referred KCs, and those feature facts should be declared in new KC.

3. Check conflict of fact definitions and design the transformers

The names of facts in two KCs should be unified. For example, if a KC use “fever” to

express a rise in the temperature of the body, the other KC shouldn’t use “pyrexia” to express the same concept. However, if needed, the transformer can be designed according to type of fact value and the meaning of facts.

4. Acquire knowledge of the new concept The step is similar to Step 6 in Section 4.1.

4.4.3 Refinement

Knowledge acquisition can be divided into two phases, initial phase and refinement phase, in which the initial knowledge base is refined to produce a high performance system [GWP88] [KIN01]. In this phase, the knowledge base should be corrected through a debug process and the relationships between KCs may be refined, e.g., the common concept of KCs can be extracted into an independent KC.