A Definition of Year 2000 conformity requirements

(The following document is included in its entirety to comply with copyright provisions for the reproduction of SAA/SNZ MP77:1998 A Definition of Year 2000 conformity requirements.)

(i) General explanation
(ii) General notes


This Miscellaneous Publication addresses what is commonly known as year 2000 conformity (also known as century or millennium compliance). It provides a definition of this expression and sets out requirements for equipment and products which use dates and times.

This Miscellaneous Publication is equivalent to British Standards Institution (BSI) document DISC PD 2000-1, A Definition of Year 2000 Conformity Requirements, but has been re-keyed to facilitate reproduction on the Internet. The only variations from the BSI document are the deletion of the list of British contributing organisations from the third paragraph of the Introduction, and the numbering of the clauses.

This document replaces the previous, initial version, but does not change its requirements. Additional information has been provided in the Amplification which will assist in the interpretation of the Definition and the four Rules.

While every care has been taken in developing this Miscellaneous Publication, Standards Australia, Standards New Zealand, BSI and the contributing organisations accept no liability for any loss or damage caused, arising directly or indirectly, in connection with reliance on its contents, except to the extent that such liability may not be excluded at law. Independent legal advice should be sought by any person or organisation intending to enter into a contractual commitment relating to year 2000 conformity requirements.

NOTE: Additional information on year 2000 conformity is available in--

(a) SAA HB99--1997, Addressing the comparison of dates for the year 2000 and beyond; and
(b) SAA/SNZ HB104:1997, A guide to year 2000 compliance.
(c) SAA HB120--1998, Managing year 2000 conformity--A code of practice for small and medium enterprises.
(d) SAA HB121--1998, Year 2000 compliance measures for personal computers.


Year 2000 conformity shall mean that neither performance nor functionality is affected by dates prior to, during and after the year 2000.

In particular--

(a) Rule 1 - No value for current date will cause any interruption in operation.
(b) Rule 2 - Date-based functionality must behave consistently for dates prior to, during and after year 2000.
(c) Rule 3 - In all interfaces and data storage, the century in any date must be specified either explicitly or by unambiguous algorithms or inferencing rules.
(d) Rule 4 - Year 2000 must be recognised as a leap year in terms of handling both the 29th of February and day 366.


(i) General explanation

Problems can arise from some means of representing dates in computer equipment and products and from date-logic embedded in purchased goods or services, as the year 2000 approaches and during and after that year. As a result, equipment or products, including embedded control logic, may fail completely, malfunction or cause data to be corrupted.

To avoid such problems, organisations must check, and modify if necessary, internally produced equipment and products and similarly check externally supplied equipment and products with their suppliers. The purpose of this Miscellaneous Publication is to allow such checks to be made on a basis of common understanding.

Where checks are made with external suppliers, care should be taken to distinguish between claims of conformity and the ability to demonstrate conformity.

Specific comment is as follows:

(a) Definition

(i) MP77 is solely concerned with the performance and functionality of a single version, release or system. It does not address differences in performance or functionality between different versions, releases or systems.(ii) Variations in performance immeasurably small in the context of use do not make a version, release or system non-conformant.

(b) Rule 1

(i) This rule is sometimes known as general integrity.(ii) If this requirement is satisfied, roll-over between all significant time demarcations (e.g. days, months, years, centuries) will be performed correctly.(iii) Current date means today's date as known to the equipment or product, i.e. the actual date of operation.

NOTE: This refers to normal operation and does not prevent testing.

(c) Rule 2

(i) This rule is sometimes known as date integrity.(ii) This rule means that all equipment and products must calculate, manipulate and represent dates correctly for the purposes for which they were intended.(iii) The meaning of functionality includes both processes and the results of those processes.(iv) If desired, a reference point for date values and calculations may be added by organisations; e.g. as defined by the Gregorian calendar.(v) No equipment or product shall use particular date values for meanings; e.g. '99' to signify 'no end value' or 'end of file' or '00' to mean 'not applicable' or 'beginning of file', unless the values in question lie outside its possible date range.

(d) Rule 3

(i) This rule is sometimes known as explicit/implicit century.(ii) This rule covers two general approaches, as follows:

(a) Explicit representation of the year in dates: e.g. by using four digits or by including a century indicator. In this case, a reference may be inserted (e.g. 4-digit years as allowed by AS 3802--1989[1] ) and it may be necessary to allow for exceptions where domain-specific Standards (e.g. Standards relating to Electronic Data Interchange, Automatic Teller Machines or Bankers Automated Clearing Services) should have preference.

(b) The use of inferencing rules: e.g. two-digit years with a value greater than 50 imply 19xx, those with a value equal to or less than 50 imply 20xx. Rules for century inferencing as a whole must apply to all contexts in which the date is used, although different inferencing rules may apply to different date sets. Where any date elements is represented without a century, the correct century shall be unambiguous for all manipulations involving that element.

(e) Rule 4

A leap year is defined in AS/NZS 3802 as follows: "year, leap: In the Gregorian calendar, a year which has 366 days. A leap year is a year whose number is divisible by four an integral number of times, except that if it is a centennial year it shall be divisible by four hundred an integral number of times". Thus, for example, 2000 is a leap year but 1900 is not.

(ii) General notes

For Rules 1 and 2 in particular, it is recommended that allowable ranges for values of current date and dates to be manipulated be documented, realising that all systems have some limitations on the valid date ranges. The ranges may relate to one or more of the feasible life-span of equipment or products or the span of dates required to be represented by the organisation's business processes. Tests for specifically critical dates may also be added (e.g. for leap years, end of year, etc.). Organisations may wish to append additional material in support of local requirements. Where the term 'century' is used, clear distinction should be made between the 'value' denoting the century (e.g. 20th) and its representation in dates (e.g. 19xx); similarly, 21st and 20xx. In order to encourage a uniform approach to date fields, organisations may wish to consider following the Commonwealth of Australia's convention for expressing the date field- CCYYMMDD

First Published as SAA/SNZ MP77:1998
Second edition, November 1998

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