The Data Model Resource Book, Volume 3: Universal Patterns for Data Modeling

Silverston c06.tex V2 - 11/21/2008 3:09am Page 254

254 Chapter 6 ■ Status: The States of Data

from the date (or date and time) events, and doesn’t redundantly capture

them as attributes. For example, instead of maintaining an indicator to capture

that an event occurred and then a status datetime attribute to record when it

happened (or when it is scheduled to happen), we can accomplish this with a

single attribute capturing the event that occurred as well as when it happened.

In this pattern you also saw an order opened from date and order closed

thru date that show statuses that have a time span. An event may happen at

a point in time, such as the date and time that an order is received, and some

events happen over time, such as an order being opened and subsequently

closed at a point in time. Hence, some statuses are ‘point in time,’ such as

order received datetime, and others are valid over a ‘range of time.’ I t is

possible that a status has no time component; for example a shipment overdue

indicator may indicate that a shipment is overdue, but has no time associated

with it.

When you maintain all of the related statuses for an entity in a single place, it

is easier for interested parties in an enterprise to see the different perspectives

different groups have of the statuses for an entity. It draws out the different

vocabulary that an enterprise has for similar concepts. In the example from ...