ERROR DESCRIPTION ON ALGEBRAIC SPECIFICATION AND ITS AUTOMATIC ADDITION

We define an algebraic specification having a framework for error hand ling and give an algorithm for automatically appending error descripti on. Generally, error description in algebraic specification is so comp licated that it is difficult to comprehend and inconsistencies arise i f handwritten. Therefore, it is effective to add error description aut omatically to algebraic specification that has no error description an d without creating any inconsistency. Error constructors are introduce d that represent error values as a framework for error handling. When there exists a term which is not equal to any constructor term, an equ ation to equalize the term and an error constructor are appended. To a void inconsistency, i.e., normal value and error value become equal, w e distinguish three kinds of variables. Some variables can be substitu ted for only by normal terms, some variables can be replaced only by e rror terms and some variables can be replaced by any term. Moreover, w e show correctness of automatic error description addition; i.e., part itioning of terms in the normal part of sort is preserved before and a fter error description addition.