Question 8/X - Maintenance of SDL
(Continuation of Question 1/X studied in 1985-1988)

Considering that

(a) SDL is now completely defined in Recommendation Z.100 and that
revisions might become necessary to fix future detected problems;

(b) several tools are available to support various aspects of language
application and that several others are under development, so that it is
absolutely required to keep the language stable to avoid invalidating
existing tools wasting significant economic investment, and to foster
new tool development;

(c) educational material is available, but it should continue to be
updated and improved;

(d) the user community is very large and support is required, with
particular attention to the application of SDL by other CCITT Study
Groups;

(e) the number of specifications based on SDL is very large and keeps
growing, and the stability of the language is required to avoid
invalidating existing specifications;

(f) SDL is currently used mostly to support informal specification but
its capabilities allow also the support of formal specification which
would result in derived benefits in the implementation of system their
testing and exploitation;

(g) evolution in the application of the language and in the target area
might require language enhancement;

(h) cooperation has been established with ISO and effective results
gained and that work in the area of FDT will continue within ISO;

(i) it is important to users of SDL that misinterpretation of Z.100 is
avoided to achieve conformance of implemented systems with their
specifications and also to prevent proliferation of dialects of the
language,

What new Recommendations, changes to existing Recommendations,
requirements, or other provisions are required for:

1. Z.100 Maintenance,

2.support of SDL Users (including aspects of integration of SDL
specifications with specifications produced in natural informal
language, in LOTOS or others),

3. furthering the use of formal specification,

4. collaboration with ISO,

5.ensuring that the use of Z.100 is in compliance with the
Recommendation?

ANNEX

(to Question 8/X)

Introduction

In order to promote the usage of SDL, it must be kept stable. Stability
will allow the implementation of tools, educational material and the use
of SDL within industrial projects. It is essential that a list of
changes is maintained during the next study period, instead of
formulating new drafts of the Recommendation text which tends to hide
minor changes. At the end of the study period, the list of changes or a
new Recommendation text will be issued, as appropriate.

In the following, guidelines are proposed which prescribe how SDL should
be maintained in the next study period.

Terminology

- An error is an internal inconsistency within Z.100.

-An open item is a problem identified but not solved during the past
study period. The open items from the 1984-1988 study period are:

-delay on channels;

- explicit constructs for non determinism in SDL;

- transformation of labels in shorthand notations.

-A deficiency occurs when during actual usage, the Z.100 is found to be
deficient.

Rules for maintenance

1. When an error is detected in Z.100, it must be corrected. The
correction of an error should imply as small a change to the language as
possible.

2. Except for error corrections and solutions to open items, changes to
SDL may only be considered as a result of a formal request for solution
of a problem by a substantial user community (e.g. another Study Group
within the CCITT). The SDL group should first look for a solution within
the existing language.

3. All changes not resulting from an error correction of the language
must be extensions, which do not invalidate existing SDL 1988.

4. During the study period all changes are recorded in a "Master List of
Changes". This list covers both Z.100 and its annexes (e.g. the User
Guidelines and the Formal Definition). No new version of Z.100 will be
issued until the end of the study period.

5. If the definition given in Z.100 is deficient, the formal definition
(Annex F) must be consulted. Deficiencies in Z.100 are recorded in an
"Interpretation Document". At the end of the study period, items from
this document may be considered in order to make the language definition
more complete.