Language Support for Changeable Systems

by Ivar Jacobson

First OOPSLA conference
=============================

Below I annotate some of the text in the paper: The paper text
starts with:
OOPSLA 86:

followed by my annotation.

All quotes from section 6.

What is missing from this paper is a systematic mechanism to define
sets of join points as with Demeter's traversal specifications
and AspectJ's pointcuts. 

-- Karl Lieberherr


OOPSLA 86:
... system development as a change activity ...

This matches well with the intent of AOSD.

OOPSLA 86:
Let us refer to an existing set of services with their objects by 
the invented word 'existion', and refer to the extended 
set of services as an extension. 

exisition = base program
extension = aspect

OOPSLA 86:
Extensions of existing behaviour, by which we mean that
new services are introduced but the existing services are not
changed. These changes are called functional extensions.

Has flavor of introductions.

OOPSLA 86:
Existing services are changed, which we simply call
functional changes. A new version of an existing service is
installed.

Has flavor of aspects.


OOPSLA 86:
The second case means that while an existion is executed
atomically, the extension may 'intervene' at specified points.
When the extension is executed, the control will be returned to
the existion which now continues its atomic action. More than
one extension may intervene in the execution of an existion. A
probe specifies where the intervention is required in the
execution of an existion.

points = join points = probes

OOPSLA 86:
We must provide such constructs so that the extension can be
described without changing the existion, i.e. the existing
service and object definitions. They must not be changed, since
they describe well working existing services which in this case
must not change.

aspect text is separate
base oblivious of aspect

OOPSLA 86:
The idea is to provide an extension service (or object) with a
list of probes (fig.7). A probe specifies an insertion point in
the graph of the extended service (or object). During
interpretation of a transition path, a service instance or an object
instance in the existion allows the desired statements of the
extension (service or object) to intervene.

list of probes = set of join points = pointcut

OOPSLA 86:
An extension may itself be treated as an existion and be
intervened by another extension.

An aspect may advise an aspect.

OOPSLA 86:
new ideas include: ...
the inclusion of source language features for system evolution
offering change orientation.