Re: Let's cover this one more time...

[cstump@levtech.com (Charles Stump)]

In article A04713@huachuca-emh17.army.mil, Nick Sizemore <sizemore@HUACHUCA-EMH17.ARMY.MIL> () writes:
>    In response to:
>
>    > Date:    Wed, 16 Nov 1994 15:35:40 EST
>    > From:    CONDIC@PSAVAX.PWFL.COM
>    >          Marin David Condic, 407.796.8997, M/S 731-93
>    > Subject: Let's cover this one more time...
>
>         I am aware of reverse engineering/conversion tools from:
>
>    Scandura          - PRODOC re/Nu FORTRAN-Ada WorkBench
>    Reasoning Systems - REFINE/<lang> series
>    McCabe Associates - (don't recall tool name).
>
>         There are others, but these are some I have seen in various
>    literature sources for several years, so I assume they have had some
>    commercial success.  I have not used these but have aquired literature
>    for others in my organization.
>
>         Is there some reason, either in priciple or in practice, why such
>    tools (as opposed to the line by line 'converters') are out of the
>    question for the project described?  I do know of at least one company
>    locally which used the McCabe tools to re-engineer an Ada system
>    (i.e., no conversion) and was pleased with the results.  Just asking -
>    I have no vested interest.

For starters, line-by-line translation is usually a bad answer. You end
up with an unmaintainable, unreadable Ada system that looks just like
the original. That is, your Ada code will look like FORTRAN or Jovial or
whatever. 

Using something like REFINE/Ada (mentioned above), very good translation
and porting environments can be built. A good soultion is to have a 
flexible, extensible translation environment that is tailored to
each translation task. This type of tool can take advantage of info.
like documentation, design knowlege, developer's input, coding standards,
 etc. in order to help do a better job of translation.

With this type of tool, you can do "intelligent" translation. Lets take 
FORTRAN for example. You reverse engineer the FORTRAN and analyze its
semantics. FORTRAN is a flat langauge. No nesting. Line-by-line translation
usually yields Ada that is flat. That is, VERY bad Ada. What should be 
done is for the tools to examine the FORTRAN and nest units and data
based on their usage in the system. In this way, globals (COMMONS) and
units can be placed at the correct level and good encapsulation and
data hiding enforced in the generated Ada code. 

Another example of things that a translation tool should fix are
parallel arrays. Standard FORTRAN does not have records. A common 
practice is to use multiple arrays and a special varialbe that 
indexes all the arrays. In this way, each array is used like a field
in a record. This activity should be identified by a tool and correctly 
translated into records in the traget language.

Another very usefull capability is a tool to allow Ada packages to be 
generated. Many older systems contain utilities and i/o functions that
are not of much concern during the translation. These units should be 
tagged in some way that they become Ada packages which are withed by 
those units that use them.

Basically, language translation is not easy. Any one who says it is 
wrong. Run away from them very quickly! At this time, good language
translation is, in my opinion, not totally automateable. The majority of
it is. The "trick" is to have sufficient tool and process support to 
allow the non-automateable parts to be accomplished without destroying 
the project.

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