- Email: [email protected]
Quality Management in Chemical Process Control Expert Systems
9c-Ol 1
Copyright © 1996 IFAC 13th Triennial World Congress, San Francisco, USA
QUALITY MANAGEMENT IN CHEMICAL PROCESS CONTROL EXPERT SYSTEMS
Peter Szczurko*, Kai Finke**, Dorothee Hoberg**
* RWTH Aachen, **
Informatik V, Ahornstr. 55, D-52056 Aachen, Germany [email protected] Henkel KGaA, TIS-I Engineering Systems, 40191 Diisseldoif, Germany {kai,finke, [email protected]
Abstract: The reliability of Process Control Expert Systems (PCX) can be guaranteed only by comprehensive test methods. The knowledge acquisition process as well as the carefully applied test methods are important factors in increasing the acceptance of automatic systems even in controlling complex chemical processes. The quality of product and process knowledge and the quality of the software system from the technical point of view has to be considered with the same consciousness. In this paper we describe how formal test methods are used during a PCX development process and how the development process itself is guided intuitively by knowledge engineers in five steps. An investigation of a concrete PCX development process based on several interviews at a major German chemicals company is the basis for a quality process model which is described in detail. Keywords: process control, quality control, automation, testability, PCX, human factors
1. HIGH QUALITY PROCESSES
ate test environment as well as the development process of the PCX itself are special interests of the company.
Increasing customer demands on products and processes cause appropriate quality management activities. According to ISO 9000 part 3 systematic, repeatable, and documented test procedures are required especially for highly automated chemical processes. Henkel KGaA, a major German chemicals company pursues the goal to raise the quality consciousness of every employee. Even in chemical processes the company invests a huge effort in receiving a quality certificate (Witzke, R., 1994) of the developed software for process control. The requirements for complexity, ease of maintenance, and the ability to manipulate large volumes of data are reasons why AI techniques, e.g. Process Control Expert Systems (PCX) have been successfully applied. The quality of the PCX software, the knowledge acquisition process, the development and applicability of an appropri-
An investigation of test methods for knowledge based systems has shown that conventional test methods used in software quality management have to be adapted for special expert system development requirements (Coulibaly, A., 1993). As we can see in specific literature on knowledge based process control, testing only plays a marginal role, mostly in connection with the question on how to embed PCX in a general CIM architecture (Wallmtiller, E., 1990 and Yeomans, R.W. et aI., 1991). A comprehensive computerized environment for PCX testing and metrication called FAITH (Fault Analysis and Integrative Testing in Heprox) (Finke, K., et al., 1994) has been developed for a PCX shell called HEPROX (Soltysiak, R., 1989) which is the standard development PCX tool for Henkel. The expert system shell is based on a host target architecture (see
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The need of abstraction mechanisms and formal representations as a basis for automatism confronts the operators with a new way of thinking. The consideration with knowledge representation and inference mechanisms reduces existing cognitively and intuitively used actions. Although the experience knowledge will be structured and formalized the often praised instinct for the optimal regulation of processes will be replaced by rational ways of thinking and behavior. Improvement phase On the basis of the explicit abstract representations the experts give constructive remarks to improve the knowledge base. The correctness will be proved in further team sessions and meetings together with the operators. Detailed questions like, which values are measured by an instrument or which states can be calculated from combined measurements, lead to a considerable improvement of the existing knowledge. Furthermore the consideration of so called external specifications which consist of explicitly given documents of PCX requirements as well as the behavior of the PCX in certain alarm situations is a prerequisite for the knowledge base inspection as well as the blackbox test in the test environment FAITH. Refinement phase The PCX development team generates a lot of test cases which should cover all decision paths as far as possible. The number of test cases depends directly on the number of decision nodes within a PCX decision tree. As an example for the sewage control PCX exist about 200 test cases documented and executed (see also table 1). The results of the PCX in every given test case are discussed together with the operators with the goal to refine the knowledge base using the abstraction mechanisms offered by HEPROX namely using strategies and substrategies. In case of obviously wrong PCX decisions the traceability of decisions plays a main role in the refinement phase. Only a comprehensive understanding of the whole decision process can reduce the operators breach of trust which arises because of the detected errors. During the development of the sewage control PCX about 50 errors have been detected and eliminated. Review / test phase During this phase the already existing PCX is integrated in the process. Although this is done without any competence changing the process, all the measured process values are given to the PCX. The process situation as well as the decisions are documented and discussed later with the operators. For an evaluation of the PCX in problematic situations the behavior of the PCX is observed by simulating known critical situations. Especially for this reason test cases are generated and executed in the process environment. Blackbox
test cases derived from the external specifications as well as whitebox test cases which are generated from the internal structure of the PCX knowledge will be executed equally. We know from experience that in this phase only few errors are detected because even the problematic situations are covered by a test case which is already investigated in the previous phase. Additionally to the validation of the PCX decisions the usual interface and integration tests within the process environment are performed (see Fig. 1).
6. EXPERIENCE In interviews with the knowledge engineers and users we established the fact that during the PCX development using the test environment FAITH the prototyping process was supported appropriately. It was easy for the developer to get a feeling for the knowledge base and its quality looking at the metric information generated during the various test phases. Feedback information like error messages and improvement hints rises step by step the trust in the system even because the boring and lengthy regression test was automated. In the development of a sewage control PCX, FAITH reduces the regression test effort to 30 %. As a side effect, the implemented metrics give adequate help in estimating the knowledge base quality from a structural point of view. We found out that the procedural share is the most important metric. The existence of a high procedural share means that the number of decision paths increases enormous because of the formal description of the nodes. The fact is that the whitebox test considers two results per node (FALSE, TRUE) although only one is used (always TRUE). From our experience we know that a value higher than 10 % disables exhaustive tests in most cases. The very success of PCX is not only a consequence of the establishment and carefully application of software quality methods but also a service of the knowledge engineer. The goal of the PCX development team should not only be reduced to reach the companies goal but also to consider the interests of every involved team member. The consideration of organizational and personnel aspects was remarked as very important for a successful PCX development (see Fig. 5). The appropriate technical environment which is given by HEPROX, FAITH and several techniques for knowledge acquisition, visualization and refinement is only one layer for the quality concept which is followed in developing successful PCX at Henkel. The application of an expert system in process control causes changes of work spaces which requires additional qualifications of the involved operators. It has been shown that fears and doubts have to be eliminated to ensure that the operators understanding of a PCX means positive work changes with more responsibility and less routine work.
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This is a prerequisite for an efficient cooperation between knowledge engineers and plant operators.
ACKNOWLEDGEMENTS
The acceptance of PCX has been increased because both developer and user have the opportunity to participate in all steps of PCX development. In fact, we noticed that with the help of FAITH, the work itself was made more interesting. Generally, the use of FAITH substantially reduces the human test effort while improving the quality of PCX significantly.
This work has been realized within a cooperation between the department of computer science V at the RWTH Aachen and the department of engineering systems at Henkel KGaA. We appreciate the excellent cooperation with this team and the willingness to give expressive information during the held interviews.
Is has been shown that the development process has been guided in an excellent manner by the knowledge engineer. This includes the carefully preparation and execution of necessary development tasks as well as the ability to motivate the involved plant operators creating a high quality PCX. In fact the knowledge engineer at Henkel is female, which may be a reason for the successful collaboration in the development team. It can be shown by several empirical studies that women are thinking more realistically, that they are more pragmatic and that they lead a conversation with more feelings for important issues than their male colleagues (Schinzel, B., 1991). In this given case it can be confirmed that the social competence of the knowledge engineer was a main factor for efficient and successful work.
REFERENCES
Until now several PCX have been designed and implemented with the use of the above mentioned development environment facilitating the knowledge acquisition process and prototyping. The given quality process model has not been described until now in detail, but has been applied intuitively by the involved knowledge engineers with great success. Although we hasten to acknowledge that this case study is in no way statistically significant, it may help to explain the stringent quality requirements placed on PCX in the company, even at the cost of system intelligence.
Fig. 5. Quality facets in HEPROX PCX development
Bologna, S., Vaelisuo, H. (1991), Deep knowledge and rigorous engineering practice, In Dependability of Artificial Intelligence Systems (DAISY-9J), (Schildt, Retti, Ed.), North-Holland,73-90. Coulibaly, A. (1993), Development of test methods for knowledge based systems, (in German), Diploma Thesis, RWTH Aachen, Informatik V. Deming, W.E. (1986), Out of the Crisis, MIT, Cambridge. Finke K. (1993), Systematic Testing of Process Control Expert Systems, (in German), Diploma Thesis, RWTH Aachen, Informatik V. Finke K., Jarke M., Szczurko P., Soltysiak R. (1994), FAITH in Process Control Expert Systems, Proc. 11 th European Conference on Artificial Intelligence (ECAl94), Amsterdam (NL), 8th-12th August 1994 ISO 3511 (1977), Process measurement control functions and instrumentation - symbolic representation, Part Ill. Kuipers, B., Qualitative reasoning - modeling and simulation with incomplete knowledge, Automatica 25, 4. Lane, N.E. (1986), Global issues in evaluation of expert systems, Proc. IEEE Int!. Con! on Systems, Man and Cybernetics, Atlanta 1986, 121-125. Schinzel, B. (1991), Frauen in Informatik, Mathematik und Technik, Informatik Spektrum, 2-1991. Soltysiak, R. (1989), HEPROX, eine Expertensystemshell ftir ProzeBftihrungsaufgaben", Automatisierungstechnische Praxis, Nr. 31, 2/1989. Stucky, W., Oberweis, A. (1992), Zur Beherrschbarkeit des Entwicklungsprozesses komplexer Software-Systeme, Forschungsbericht 242, Univ. Karlsruhe. Wallmtiller, E. (1990), Software-Qualitiitssicherung in der Praxis, Hanser-Verlag. Witzke, R. (1994), Zertifizierung von Qualitatsmanagement-Systemen bei Softwareherstellern, Theorie und Praxis der Wirtschaftsinformatik, Heft 175, Jan. 1994. Yeomans, R.w., Choudry, A., Ten Hagen, PJ.W. (1991), Design Rules for a CIM System, North Holland.
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Copyright © 1996 IFAC 13th Triennial World Congress, San Francisco, USA
QUALITY MANAGEMENT IN CHEMICAL PROCESS CONTROL EXPERT SYSTEMS
Peter Szczurko*, Kai Finke**, Dorothee Hoberg**
* RWTH Aachen, **
Informatik V, Ahornstr. 55, D-52056 Aachen, Germany [email protected] Henkel KGaA, TIS-I Engineering Systems, 40191 Diisseldoif, Germany {kai,finke, [email protected]
Abstract: The reliability of Process Control Expert Systems (PCX) can be guaranteed only by comprehensive test methods. The knowledge acquisition process as well as the carefully applied test methods are important factors in increasing the acceptance of automatic systems even in controlling complex chemical processes. The quality of product and process knowledge and the quality of the software system from the technical point of view has to be considered with the same consciousness. In this paper we describe how formal test methods are used during a PCX development process and how the development process itself is guided intuitively by knowledge engineers in five steps. An investigation of a concrete PCX development process based on several interviews at a major German chemicals company is the basis for a quality process model which is described in detail. Keywords: process control, quality control, automation, testability, PCX, human factors
1. HIGH QUALITY PROCESSES
ate test environment as well as the development process of the PCX itself are special interests of the company.
Increasing customer demands on products and processes cause appropriate quality management activities. According to ISO 9000 part 3 systematic, repeatable, and documented test procedures are required especially for highly automated chemical processes. Henkel KGaA, a major German chemicals company pursues the goal to raise the quality consciousness of every employee. Even in chemical processes the company invests a huge effort in receiving a quality certificate (Witzke, R., 1994) of the developed software for process control. The requirements for complexity, ease of maintenance, and the ability to manipulate large volumes of data are reasons why AI techniques, e.g. Process Control Expert Systems (PCX) have been successfully applied. The quality of the PCX software, the knowledge acquisition process, the development and applicability of an appropri-
An investigation of test methods for knowledge based systems has shown that conventional test methods used in software quality management have to be adapted for special expert system development requirements (Coulibaly, A., 1993). As we can see in specific literature on knowledge based process control, testing only plays a marginal role, mostly in connection with the question on how to embed PCX in a general CIM architecture (Wallmtiller, E., 1990 and Yeomans, R.W. et aI., 1991). A comprehensive computerized environment for PCX testing and metrication called FAITH (Fault Analysis and Integrative Testing in Heprox) (Finke, K., et al., 1994) has been developed for a PCX shell called HEPROX (Soltysiak, R., 1989) which is the standard development PCX tool for Henkel. The expert system shell is based on a host target architecture (see
7177
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7179
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The need of abstraction mechanisms and formal representations as a basis for automatism confronts the operators with a new way of thinking. The consideration with knowledge representation and inference mechanisms reduces existing cognitively and intuitively used actions. Although the experience knowledge will be structured and formalized the often praised instinct for the optimal regulation of processes will be replaced by rational ways of thinking and behavior. Improvement phase On the basis of the explicit abstract representations the experts give constructive remarks to improve the knowledge base. The correctness will be proved in further team sessions and meetings together with the operators. Detailed questions like, which values are measured by an instrument or which states can be calculated from combined measurements, lead to a considerable improvement of the existing knowledge. Furthermore the consideration of so called external specifications which consist of explicitly given documents of PCX requirements as well as the behavior of the PCX in certain alarm situations is a prerequisite for the knowledge base inspection as well as the blackbox test in the test environment FAITH. Refinement phase The PCX development team generates a lot of test cases which should cover all decision paths as far as possible. The number of test cases depends directly on the number of decision nodes within a PCX decision tree. As an example for the sewage control PCX exist about 200 test cases documented and executed (see also table 1). The results of the PCX in every given test case are discussed together with the operators with the goal to refine the knowledge base using the abstraction mechanisms offered by HEPROX namely using strategies and substrategies. In case of obviously wrong PCX decisions the traceability of decisions plays a main role in the refinement phase. Only a comprehensive understanding of the whole decision process can reduce the operators breach of trust which arises because of the detected errors. During the development of the sewage control PCX about 50 errors have been detected and eliminated. Review / test phase During this phase the already existing PCX is integrated in the process. Although this is done without any competence changing the process, all the measured process values are given to the PCX. The process situation as well as the decisions are documented and discussed later with the operators. For an evaluation of the PCX in problematic situations the behavior of the PCX is observed by simulating known critical situations. Especially for this reason test cases are generated and executed in the process environment. Blackbox
test cases derived from the external specifications as well as whitebox test cases which are generated from the internal structure of the PCX knowledge will be executed equally. We know from experience that in this phase only few errors are detected because even the problematic situations are covered by a test case which is already investigated in the previous phase. Additionally to the validation of the PCX decisions the usual interface and integration tests within the process environment are performed (see Fig. 1).
6. EXPERIENCE In interviews with the knowledge engineers and users we established the fact that during the PCX development using the test environment FAITH the prototyping process was supported appropriately. It was easy for the developer to get a feeling for the knowledge base and its quality looking at the metric information generated during the various test phases. Feedback information like error messages and improvement hints rises step by step the trust in the system even because the boring and lengthy regression test was automated. In the development of a sewage control PCX, FAITH reduces the regression test effort to 30 %. As a side effect, the implemented metrics give adequate help in estimating the knowledge base quality from a structural point of view. We found out that the procedural share is the most important metric. The existence of a high procedural share means that the number of decision paths increases enormous because of the formal description of the nodes. The fact is that the whitebox test considers two results per node (FALSE, TRUE) although only one is used (always TRUE). From our experience we know that a value higher than 10 % disables exhaustive tests in most cases. The very success of PCX is not only a consequence of the establishment and carefully application of software quality methods but also a service of the knowledge engineer. The goal of the PCX development team should not only be reduced to reach the companies goal but also to consider the interests of every involved team member. The consideration of organizational and personnel aspects was remarked as very important for a successful PCX development (see Fig. 5). The appropriate technical environment which is given by HEPROX, FAITH and several techniques for knowledge acquisition, visualization and refinement is only one layer for the quality concept which is followed in developing successful PCX at Henkel. The application of an expert system in process control causes changes of work spaces which requires additional qualifications of the involved operators. It has been shown that fears and doubts have to be eliminated to ensure that the operators understanding of a PCX means positive work changes with more responsibility and less routine work.
7181
This is a prerequisite for an efficient cooperation between knowledge engineers and plant operators.
ACKNOWLEDGEMENTS
The acceptance of PCX has been increased because both developer and user have the opportunity to participate in all steps of PCX development. In fact, we noticed that with the help of FAITH, the work itself was made more interesting. Generally, the use of FAITH substantially reduces the human test effort while improving the quality of PCX significantly.
This work has been realized within a cooperation between the department of computer science V at the RWTH Aachen and the department of engineering systems at Henkel KGaA. We appreciate the excellent cooperation with this team and the willingness to give expressive information during the held interviews.
Is has been shown that the development process has been guided in an excellent manner by the knowledge engineer. This includes the carefully preparation and execution of necessary development tasks as well as the ability to motivate the involved plant operators creating a high quality PCX. In fact the knowledge engineer at Henkel is female, which may be a reason for the successful collaboration in the development team. It can be shown by several empirical studies that women are thinking more realistically, that they are more pragmatic and that they lead a conversation with more feelings for important issues than their male colleagues (Schinzel, B., 1991). In this given case it can be confirmed that the social competence of the knowledge engineer was a main factor for efficient and successful work.
REFERENCES
Until now several PCX have been designed and implemented with the use of the above mentioned development environment facilitating the knowledge acquisition process and prototyping. The given quality process model has not been described until now in detail, but has been applied intuitively by the involved knowledge engineers with great success. Although we hasten to acknowledge that this case study is in no way statistically significant, it may help to explain the stringent quality requirements placed on PCX in the company, even at the cost of system intelligence.
Fig. 5. Quality facets in HEPROX PCX development
Bologna, S., Vaelisuo, H. (1991), Deep knowledge and rigorous engineering practice, In Dependability of Artificial Intelligence Systems (DAISY-9J), (Schildt, Retti, Ed.), North-Holland,73-90. Coulibaly, A. (1993), Development of test methods for knowledge based systems, (in German), Diploma Thesis, RWTH Aachen, Informatik V. Deming, W.E. (1986), Out of the Crisis, MIT, Cambridge. Finke K. (1993), Systematic Testing of Process Control Expert Systems, (in German), Diploma Thesis, RWTH Aachen, Informatik V. Finke K., Jarke M., Szczurko P., Soltysiak R. (1994), FAITH in Process Control Expert Systems, Proc. 11 th European Conference on Artificial Intelligence (ECAl94), Amsterdam (NL), 8th-12th August 1994 ISO 3511 (1977), Process measurement control functions and instrumentation - symbolic representation, Part Ill. Kuipers, B., Qualitative reasoning - modeling and simulation with incomplete knowledge, Automatica 25, 4. Lane, N.E. (1986), Global issues in evaluation of expert systems, Proc. IEEE Int!. Con! on Systems, Man and Cybernetics, Atlanta 1986, 121-125. Schinzel, B. (1991), Frauen in Informatik, Mathematik und Technik, Informatik Spektrum, 2-1991. Soltysiak, R. (1989), HEPROX, eine Expertensystemshell ftir ProzeBftihrungsaufgaben", Automatisierungstechnische Praxis, Nr. 31, 2/1989. Stucky, W., Oberweis, A. (1992), Zur Beherrschbarkeit des Entwicklungsprozesses komplexer Software-Systeme, Forschungsbericht 242, Univ. Karlsruhe. Wallmtiller, E. (1990), Software-Qualitiitssicherung in der Praxis, Hanser-Verlag. Witzke, R. (1994), Zertifizierung von Qualitatsmanagement-Systemen bei Softwareherstellern, Theorie und Praxis der Wirtschaftsinformatik, Heft 175, Jan. 1994. Yeomans, R.w., Choudry, A., Ten Hagen, PJ.W. (1991), Design Rules for a CIM System, North Holland.
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