The Z Standard: FAQ

Frequently Asked Questions:

N.B. This document is very out of date. Questions should be directed to those named at the end of the document, as should offers to update the questions and answers.

What is happening?

An international standard for Z is being developed as part of the programme of work of ISO committee
JTC 1/ SC22, (Programming languages, their environments and system software interfaces).

A document defining the proposed Z Standard has recently (February 1996) successfully completed a ballot for acceptance as an ISO Committee Draft. The version submitted for ballot (Version 1.2) can be downloaded from the Oxford University Computing Laboratory, via the Z Standardization Home Page.

Many comments were made in the ballot and these will be reflected in the next version of the Committee Draft and in the finally published ISO Standard. It is hoped there will shortly be an electronic comments form available, to allow comments to be made on the development of the standard.

Why is a Z standard needed?

• to improve communication among Z users.
• to provide a stable base for the development of tools, methods and training in Z and for the further development of the notation in new areas.
• to provide a means for users and other interested parties to propose input on the direction for the design of the notation.
• to ensure the description of Z is published and made available to a wide community.
• to provide a basis for the use of Z in other international standards.

Who is involved in developing the standard?

The Z Standard is being drafted, reviewed and modified by members of the Z Standards Panel. This has the title ISO Panel JTC1/SC22/WG19 (Rapporteur Group for Z).

Panel members come from many parts of the Z community.

What will the Z Standard contain?

The Z Standard is defined in a document, Z Notation, structured as follows:

• the first part provides a general introduction and defines symbols and notation. A brief statement defines what it means to conform to the standard.
• the second and main part of the document contains the definition of the notation and is structured according to the Abstract Syntax.
  For each of the main elements of Z defined by the abstract syntax, there is a subsection defining the corresponding syntax and semantics. Semantics of Z are defined using a denotational method.
• Annexes provide a complete definition of the syntaxes (including Concrete and Abstract syntaxes), Lexis, and an SGML-based Interchange Format, a definition of the Standard Mathematical Toolkit, and an account of the logical theory of Z, including a deductive system for the logic of Z and a deductive type system.

The current draft document has just over 200 pages and the final document is not likely to be much larger.

Z has been evolving for years. Will standardization put a stop to this?

One of the reasons for developing an ISO standard for Z is that, provided there are sufficient users and available experts for its continuing development, the Standard will be updated to continue to meet users' needs. The procedures for developing international standards include, and in fact require, that standards are regularly reviewed and updated.

What about Object-oriented Z?

There have been many proposals for object-oriented extensions to the Z notation. The Standards Panel made a policy decision that no specific proposal for object-oriented Z would be included in the first version of the standard. On the other hand, it is expected that a number of recent developments in the fundamental structure of the notation will make it easier to develop such extensions.

There is an object-oriented subgroup of the Standards Panel to study developments in this area; the convener of the object-oriented sub-group is Pete Young.

What is the relationship to the VDM standard?

There are many similarities between Z and VDM-SL, but also a number of profound differences.

References to comparisons of the two notations to be added here.

The two standards groups keep in close touch with each other, and several people are members of both panels, which are part of the same ISO Working Group (WG19).

How will Standard Z differ from our current understanding of Z?

To be added here:

a list of important differences between Standard Z and other descriptions of Z.

How can I get more information?

The convener of the Standards committee is John Wordsworth. The project editor is Ian Toyn.

This page is maintained by Andrew Martin.

Last updated: 19th November 1998, but remains out-of-date.