Correctness of Transformations

Correctness of Transformations
Transformations manipulate syntactic objects in a program; they are not string manipulation
rules.A transformation’s pattern and replacement are syntactically correct statements
in the subject language.The pattern of a transformation cannot match a syntactically
incorrect program,and the replacement of a transformation cannot introduce a syntactically
incorrect form into a program.The transformational process is always one of manipulating
syntactically correct programs.
In practice,most transformations we write are no more complex than the preceding
examples; the power of transformations comes from the cumulative effect of,perhaps,
thousands of applications of a few dozen transformations,each application performing
some simple,local change to a program fragment.Because transformations are applied
entirely automatically,the number of applications is of little significance to the developer
or user of the tool.
What is significant is the simplicity of each transformation; to see that an application of
a simple transformation preserves the meaning of a program is usually trivial.(However,
because transformations are formal objects,formal proofs can be used to guarantee the
correctness of more complex transformations (Winter and Boyle,1996).) Simple transformations
make reasoning about the rule easier and facilitate informal or formal proofs of
transformation termination.
If each of several transformations preserves meaning,then their combined application
also preserves meaning.Thus,an implementation derived by correctness–preserving transformations
is known to be as correct as the specification from which it is derived.
In writing transformations one attempts to identify an appropriate algebra for the forms
being manipulated.In the preceding example,these forms are Boolean expressions and
one can draw on logic,specifically de Morgan’s Laws,for the required algebra.

正确翻译如下
正确性变换变换操纵句法物体节目; 他们不是字符串操作规则.转型?收盘格局和置换语法正确陈述的主题语言.模式转型不能匹配语法错误纲领 并更换了改造,不能提出一个语法错误形成一个方案.转型过程的始终是操纵语法正确的节目.在实践中,大多数转变我们写信没有比前面例子; 电力变换来自累积的影响,也许数千名申请了数十个转变 每项申请从事一些简单的,局部改变了节目片段.因为变换应用完全自动,报名人数是没有多大意义的发展或用户的工具.什么是重要的是纯朴的每个转化; 看到一个应用一个简单的变换蜜饯的含义节目通常是小巫见大巫.(不过,因为变革是正式的物体,正式证明,可以用来担保的正确性更加复杂变换(冬季和博伊尔 1996 ) ) .简单变换,使推理的统治方便,便于进行非正式或正式证明转型终止.如果每个数变换蜜饯含义,然后结合自己的应用也蜜饯意思.因此,执行所得的正确性?cpreserving变换已知是正确的规格,从它的来源.在写作转变的一个尝试,以确定一个适当的代数形式受到操控.在上面的例子,这些形式的布尔表达式和一个可以借鉴逻辑,具体德摩根?收盘法律 对需要代数.