The Definition of Year 2000 Conformity Prepared by British Standards Institute (Document Ref: DISC PD2000-1)

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

Rule 1

"No value for current date will cause any interruption in operation"

• This rule is sometimes referred to as General Integrity;

• If this requirement is satisfied, roll-over between all significant time demarcations will be performed correctly;

• Current Date refers to today's date as known to the equipment or software.

Rule 2

"Date functionality must behave consistently for dates prior to, during and after year 2000"

• This rule is sometimes referred to as Date Integrity;

• This rule means that all equipment and software must calculate, manipulate, and represent dates correctly for the purpose for which they were intended;

• The meaning of functionality includes both processes and the results of these processes;

• If desired, a reference point for date values and calculations may be added by organisations: eg as defined by the Gregorian calender;

• No equipment or software shall use particular date values for special meanings; eg "99" to signify "no end value", or "end of file".

Rule 3

"In all interfaces and data storages, the century in any date must be specified either explicitly or by unambiguous algorithms or inferencing rules"

• This rule is sometimes known as explicit/implicit century;

• It covers two general approaches:

a)  explicit representation of the year in dates: eg 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 ISO standard 8601:1988) 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 Service) should have precedence.


b)  the use of inferencing rules: e.g. two-digit years with a greater value 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.

Rule 4

"Year 2000 must be recognised as a leap year"

• The year 2000 is a leap year, whereas the years 1800 and 1900 were not. Hence for proper compliance there must be rollover from 28-02-2000 to 29-02-2000 (and subsequently to 01-03-2000), and from 28-02-1900 to 01-03-1900.

General Notes

For rules 1 and 2 in particular, organisations may wish to specify allowable ranges for values of current date and dates to be manipulated. The ranges may relate to the feasible life-span of equipment or products and/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.

NB This material may be freely copied provided that the source is acknowledged (BSI-DISC), and it is reproduced in full.