Page 90 - DCAP305_PRINCIPLES_OF_SOFTWARE_ENGINEERING

Principles of Software Engineering

Notes Disadvantages
• Changes in data storage format affects all modules, for example if the data structure is
changed, then all the modules have to be modified to adjust to that change.
• Changes in algorithm not well supported.
• Poor stability if access to the shard data is not handled appropriately.
• Not supportive of reuse due to the dependency on the shared data.
• Enhancements not easily incorporated because of the above reasons.

An Interpreter Using Different Idioms
for the Components

ule-based systems provide a means of codifying the problem-solving know how of
human experts. These experts tend to capture problem-solving techniques as sets of
Rsituation-action rules whose execution or activation is sequenced in response to the
conditions of the computation rather than by a predetermined scheme. Since these rules are
not directly executable by available computers, systems for interpreting such rules must be
provided. Hayes-Roth surveyed the architecture and operation of rule-based systems.
The basic features of a rule-based system, shown in Hayes-Roth’s rendering as in Figure 1,
are essentially the features of a table-driven interpreter, as outlined earlier.
• The pseudo-code to be executed, in this case the knowledge base.

• The interpretation engine, in this case the rule interpreter, the heart of the inference
engine.
• The control state of the interpretation engine, in this case the rule and data element
selector.
• The current state of the program running on the virtual machine, in this case the working
memory.

Figure 1: Basic Rule-Based System

Rule-based systems make heavy use of pattern matching and context (currently relevant rules).
Adding special mechanisms for these facilities to the design leads to the more complicated
view shown in Figure 2. In adding this complexity, the original simple interpreter vanishes
in a sea of new interactions and data flows. Although the interfaces among the original
modules remain, they are not distinguished from the newly-added interfaces.
Contd...

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