Thoughts on the use of the term "Use Case" vs. "Scenario"

["Husband, Yin-Leng" <yin-leng.husband@hp.com>]

Since Ivar Jacobson first introduced the term "use case" (at the OOPSLA
conference in 1987), and James Rumbaugh used the term "scenario" in OMT
(1991), I thought we should see how these two authors defined these two
terms.

Definition of the two terms from The Unified Software Development
Process (1999, Ivar Jacobson, Grady Booch, James Rumbaugh), for what
it's worth, are:
1. "Use case - a description of a set of sequence of actions, including
variants, that a system performs that yields an observable result of
value to a particular actor." "... A use case is a piece of
functionality in the system that gives a user a result of value.  Use
cases capture functional requirements."
2. "Scenario - a specific sequence of actions that illustrates
behavior."
3. James Rumbaugh's Object Modeling Technique (OMT) defines a scenario
as: "a scenario is a sequence of events that occurs during one
particular execution of a system ... a scenario can be the historical
record of executing a system or ... experiment of executing a proposed
system."

These authors have specific meanings for the two related, but not
interchangeable terms.

There was a similar discussion in the Web Services Architecture WG on
the difference between "use case" and "usage scenario" (instead of
"scenario").
(See http://lists.w3.org/Archives/Public/www-ws-arch/2002Mar/0464.html
which had
"Basically, use cases (e.g., UML) are something more structured and
oriented to software design.  Usage scenarios are less structured, and
perhaps more abstract to illustrate broad architectural concepts.")

I suggest we do something similar to the WSA WG and adopt the term
"usage scenario" so as not to re-define terms (i.e. "use case" and
"scenario") that already have well-defined meanings in their original
context.

Suggest for wsbpel-uc purposes, we could define
Usage scenario - a description of sequence of business-level activities,
that illustrate the concepts and usages that should be standardized, and
from which functional and qualitative requirements may be derived.

Usage scenarios are descriptions in terms from end-users' domains (e.g.
sending a purchase order, purchasing a ticket, filing an insurance
claim), whereas requirements are in terms relevant to a specification's
support of functionality (e.g. shall support semantic shortcuts, support
parallel split pattern, support process compensation, support
compensation handler) and quality (e.g. shall support caching to
increase performance).