THE DEFINITION (PD2000-1:1998)

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

In particular:

  • Rule 1 No value for current date will cause any interruption in operation.

  • Rule 2 Date-based functionality must behave consistently for dates prior to, during and after year 2000.

  • 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.

  • Rule 4 Year 2000 must be recognised as a leap year.

AMPLIFICATION OF THE DEFINITION AND RULES

1. 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 document 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.

2. Amplification of the definition

  • PD2000-1 (all editions) 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.
  • Variations in performance immeasurably small in the context of use do not make a version, release or system non-conformant.

3. Amplification of the Rules

Rule 1

  • This rule is sometimes known as general integrity.
  • If this requirement is satisfied, roll-over between all significant time demarcations (e.g. days, months, years, centuries) will be performed correctly.
  • 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.]

Rule 2

  • This rule is sometimes known as date integrity.
  • This rule means that all equipment and products must calculate, manipulate and represent dates correctly for the purposes for which they were intended.
  • The meaning of functionality includes both processes and the results of those processes.
  • If desired, a reference point for date values and calculations may be added by organisations; e.g. as defined by the Gregorian calendar.
  • No equipment or product shall use particular date values for special 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.

Rule 3

    This rule is sometimes known as explicit/implicit century.

    It covers two general approaches:

    (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 ISO 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 Services) should have precedence.

    (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 element is represented without a century, the correct century shall be unambiguous for all manipulations involving that element.

Rule 4

  • A leap year is defined in ISO 8601:1988 (amended in 1991) 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.

4 General Notes

  • For Rules 1 and 2 in particular, it is recommended that the allowable ranges for values of current date and dates to be manipulated be documented, recognising that all systems have some limitation on the valid date ranges. The ranges may relate to one or more of the feasible life-spans 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.