Cambridge International AS & A Level ICT - Chapter 7 Expert Systems

1. EXPERT SYSTEMS
CAMBRIDGE INTERNATIONAL AS & A LEVEL
Anjan Mahanta
anjan.mahanta@satreephuketipc.com

2. Learning Objectives
● describe the components of an expert system and how expert systems can be used
● explain how expert systems produce possible solutions, including the process of
forward and backward chaining
● analyse the use of different processing systems
● explain how master and transaction files are used
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3. What is an expert system?
● Expert systems use a knowledge base and a set of rules to provide a diagnosis or
a recommended course of action. They can be used to solve complex problems
by reasoning, using the knowledge base they are given.
● Expert systems gather data by asking the user questions about the problem. An
initial set of questions can lead to further questions depending on the user’s
responses.
● The expert system reasons what questions it needs to ask, based on the
knowledge it is given. It will use the responses from the user to rule out various
possibilities that will allow it to eventually reach a decision or diagnosis.
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4. Expert System
● We rely on expert systems to help us with knowledge and
understanding in a particular field. We use them in the same way as
we do certain experts in our lives.
● For example, we will go to see a doctor if we have a health problem or
we will go to see a car mechanic if our car will not start.
● We can use an expert system in a similar way, it will ask us questions
about our health problem or car problem and provide us with a
diagnosis or course of action.
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5. Expert System
Building an expert system is known as knowledge engineering and it is composed of three
main components:
● the knowledge base
● the inference engine
● the user interface.
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6. Expert System
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7. Knowledge Base
● The developers of the expert system will interview a collection of experts to
build the database of knowledge.
● They will look to gain two types of knowledge from the experts.
● The first is factual knowledge. This is knowledge that is widely shared.
● The second type is heuristic knowledge. This is knowledge that is more
personal and is acquired through a range of experiences and reasoning.
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8. Knowledge Base
● Once the knowledge base is built,it can be used by the expert system to inform the
question sit needs to ask and assist in providing the results.
● Part of the knowledge base is the rules base. The rules base is a set of rules that will be
used to produce an output or decision by the expert system. These rules are used by the
inference engine as a base for reasoning, to obtain a solution to a problem ora decision.
● Each rule will contain two parts,the IF and the THEN. A rule can also have multiple IF parts
that will be joined together by Boolean operators including AND and OR.
● Most expert systems will have a knowledge based editor built into them. This allows the
knowledge base to be checked for errors and edited ad updated when needed.
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9. Inference Engine
● It will ask the user questions, and based on their answer, it will follow a line of
logic.This may then lead to further questions and eventually a final result.
● The inference engine is mostly a problem-solving tool. It organises and controls
steps to solve the problem. To do this it often uses a chaining method. It chains
together what is known as IF-THEN rules to form a line of reasoning.
● The IF part of the rule is a condition, for example IF I am hungry. The THEN part
of the rule is an action, for example IF I am hungry THEN I will need to eat.
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10. Inference Engine
● There are two main methods that can be used to obtain a result.
● The appropriate one will depend on whether the expert system is designed to
produce a final result i.e a diagnosis or course of action, or if it begins with a
known conclusion i.e. a goal.
● If the process starts with a set of conditions and chaining moves towards a final
conclusion, this is called forward chaining.
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11. Inference Engine - Forward Chaining
● In a forward chaining system, the expert system will take the data input and
match it to the knowledge and rules it contains.
● It will keep doing this until it can reach an end goal or outcome. A forward
chaining system is data driven.
● Data is gathered about the problem and then the system infers what it can from
the data to reach a conclusion.
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12. Inference Engine - Backward Chaining
● If the process starts with a known conclusion, but the path to it is unknown, the
chaining will work in reverse and this is called backward chaining.
● The system in this case has a goal or solution and the inference engine attempts
to find the evidence to prove it.
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13. User Interface
● The user interface is the way the user interacts with the expert system.
● They are often graphical in nature and have a range of selection
processes or typing methods to allow the user to provide responses.
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14. Expert System
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Advantages Disadvantages
They provide answers to questions that are outside a
user’s knowledge and experience.
They do not have the addition of common sense that
humans have. This means that their response can only be
a logical one and cannot have a creative approach.
They can aid professionals in areas where their
knowledge and experience are a little weaker.
Errors in the knowledge base or inference engine will
produce errors in the results. Therefore they are only as
good as the data and rules they are given.
As they use a logical process they are consistent in the
answers that they give.
They are not able to automatically adapt to changing
environments. This requires the knowledge base to be
changed.
They will not forget to ask a question, as all the rules and
knowledge is put into place to make sure that all data
needed is gathered.
They are expensive to produce as they require a great
deal of time and effort from experts and developers.

15. How are expert systems used?
● Medical diagnosis
● Car mechanical diagnosis
● Playing chess
● Providing financial advice
● Troubleshooting computer and printer issues
● Identifying items, for example plants and birds
● Using a telephone help desk
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18. Data Processing Systems
● There are many types of systems that process data, and a variety of ways
the processing can be carried out.
● A system that processes data will have a method to input the data, a
method to process the data and a method to output the data.
● There are three ways data can be processed these are batch, online and
real-time processing systems.
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19. Batch Processing System
● The amount of data processed by batch
processing systems is normally quite large. By
storing the data together in batches, it means
that the processing can be carried out at a time
when the system is in less demand.
● This results in less disruption to a system during
the times of the day when it could be in heavy
demand. No user interaction is required to
process the data. The system is automatically
triggered at a set time.
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20. Batch Processing System
● There are issues that can occur with a batch
processing system.
● There is a time delay for the data processing, so the
output that will be provided is not always readily
available.
● Also, if there is an error with an input,this will not be
recognised until a later date when the data is
processed.
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21. Batch Processing System
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22. Online Processing System
● An online processing system is sometimes known as an interactive processing system.
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23. Real time Processing System
A real-time processing system processes data as soon as it has been input.
They are normally used when the immediacy of the data is vital.
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24. Real time Processing System
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26. File Types
For data to be processed it is often stored first. This can be for long periods of
time or momentarily. There are two main file types that are used to store data,
master files and transaction files.
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27. Master File
● The master file will store all of the more permanent data
about the customer or the employee. Data stored in
master files is normally more permanent in nature.
● A master file is normally a collection of fields about a
main element of a data system,for example a customer
or an employee.
● There will normally be a key field present in a master file,
such as the employee number in the example above. The
key field will be used to match transaction files to the
correct master file. 27

28. Transaction File
● The data stored in these files is normally used to update
the master file.It is more temporary in nature.
● The key field is again present in the transaction file in
order to allow it to be matched to the correct master file.
● Transaction files are useful as they can act as an audit trail
for a company to see what updates have been made to the
master file at various times.
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