Re: HOOD?

[Jean-Marie Wallut <Jean-Marie.Wallut@CST.CNES.FR>]

Franz.Kruse@erno.de (Franz Kruse) wrote:


>What is the general opinion of the Ada community about HOOD as a design
method?

>Franz Kruse

We would like to explain why we think HOOD is an excellent design method
particularly for Ada developments :

- first of all we think that the concepts of the methods are very good :
encapsulation (as in every object oriented method) but also hierarchy that
promotes the strict definition of interfaces between separate domains at
each level of the design. This last feature is very important for
prototyping and/or for shared development.

- complete corerage of the development process from the first brain storming
to the final coding with the same technology. This changes from previous
methods that used different technologies
for each phase that implies translation between several formalisms (with
risks of non respect of what was approved at the previous phase)

- One can make a strict correspondance between the explanations he gives in
the textual part of an object in his design and the code resulting from
these design decisions.
The layered approche makes this strict correspondance easy. Specially for
Ada development each feature of the method is directely implemented by an
Ada feature (a parent object is a package specification, a terminal object
as a body for implementing his "duty", an internal data is a variable in the
body etc....). Some rules have been added thant enhance the quality of the
generated Ada (for example it is forbidden to offer a data in the provided
interface of an object that is to say in an Ada specification : this avoid
data to be modified by any client of the object responsible of the data.

- More and more the design can be independant from the design tools. The
concept of SIF (Standard Interchange Format) allows to bring a design from a
tool to another one (even if the SIF does not take into account some aspects
as the graphical aspect of the solution and also if the tools do not all
implement perfectly the SIF import/export).

Our opinion is based on our personnal feeling from personnal developments
but also on the fact that at the moment each project developped in Ada in
our company is designed in HOOD and the results are good in most of the cases.

Last point to focus on is that the method is evolving to take into account
the new concepts of Ada 95 that is to say inheritance an polymorphism. These
new possiblities combined with hierarchy (as soon as one knows how to use
properly both features together) can make of HOOD an even more powerful method.

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