Timeliness Requirements

Definition

A timeliness requirement is a correctness requirement that specifies a required amount of timeliness, which is a quality factor that is defined as follows:

Timeliness

the degree to which something ensures that its data remains current (i.e., up-to-date, not obsolete).

Objectives

The typical objectives of a timeliness requirement are to ensure that time varying data:

• Is updated sufficiently often to remain correct (to within a temporal tolerance).
• Does not become significantly obsolete (e.g., to compromise calculations based upon it).
• Is current enough so that its users (human and otherwise) can depend upon it.

Measurements

Timeliness requirements are typically specified in terms of the following measurements:

• Maximum time delay between when the:
  • Data actually changes
  • All views of the data are updated.
• Maximum average time delay between data change and data views are updated.
• Minimum percentage of data views updated within a given time delay.
• Maximum percentage of data that is obsolete.

Timeliness requirements can also be specified in terms of some combination of the preceding measurements.

Examples

The following are typical examples of timeliness requirements:

• “Each display of a customer’s account balance shall be updated to its correct value within 2 seconds of the time that the actual account balance changes.”
• “The credit card processing application shall notify all affected bank computers within 10 seconds of the time that a credit card transaction is approved.”
• “When a product’s actual unit price is updated, then each displayed version of the unit price shall be updated to the correct value within 2 seconds.”
• “All stock prices being displayed to customers shall be updated within 10 seconds of the time that they are updated by the stock exchange.”
• “At least 99% of the time, the content management system shall publish new content to the web servers within an average of 5 minutes of the time that the content is approved for publication.”
• “The controller shall be notified of the new measured temperature of the chemical mixing tank within 2 seconds of each time that the temperature changes by more than 0.5 ° C.”
• “A minimum of 99% of the user account information on the user interface shall be updated within 2 seconds of its value changing.”
• “User administration shall not permit more than 0.03% of the stored user contact information to be obsolete when monthly contact lists are published.”

Guidelines

The following guidelines have been found to be useful when producing timeliness requirements:

• The scope of a timeliness requirement can be:
  • A business enterprise
  • An application
  • A component
  • A center
  • A document
• Timeliness requirements can be identified and specified in term of the following:
  
  

  Component of Requirement	Possibile Values
  Changing Data	Input data (e.g., read from a sensor) Internal data (e.g., calculated data) Output data
  Party Notified	User External application External database
  Measurement	Maximum time delay Maximum average time delay
  Units of Time	Milliseconds Seconds Minutes Hours Days

  
  
• The timeliness requirements typically vary depending on the time criticality of the data. Thus, whereas default timeliness requirements may exist, some timeliness requirements will vary depending on the data and users to be formed.
• Timeliness requirements may legitimately be considered to be performance requirement (i.e., timing requirements) rather than correctness requirement (i.e., obsolete data is data that is no longer correct).