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The work described in this book is part of the "ENGLISH BEANS" project, which is an online English learning program. Its target is to help the primary and secondary school students to improve the English learning efficiency by using the cutting-edge technologies such as Natural Language Processing, Corpus, and Knowledge Graph. "English Beans" has a multiple-level hierarchical architecture and complex structure, and it also involves a variety of third-party modules and tools. Consistency, among different modules and tools, is therefore a key problem for the purpose of the integrity of "ENGLISH BEANS" project. EXPRESS (ISO 10303-11) language was introduced into the project to describe the relative knowledge, information, and data in a semi-formal manner. Checking, analysis, simulation work then would apply on this semi-formal level to guarantee the consistency and complete of the overall system.

A correct EXPRESS model should not only be syntactically correct, but also semantically complete and consistent. In this context, the definition of consistency is that there should be no conflicting constraints in the model so that the model and all its sub-components can correctly co-exist in an instantiation.

Current approaches to EXPRESS model checking focus on syntactic and language semantic checking and on checking instance data against model constraints. The approach covered in this book is different in that it considers the issues of semantic consistency by analysis of the EXPRESS model definition.

Consistency is in part the focus of several paradigms such as UML, OWL and Constraint Programming (CP). Addressing consistency issues in those paradigms requires formal semantics and reasoning technologies that can fully cover such formal semantics. The work described here uses these formal approaches, and more particularly Constraint Programming, to provide a consistency checking environment for EXPRESS models.