My first Publication Agile-Data-Warehouse-Design-eBook | Page 65

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Chapter 2
Determining the Story Type
Knowing the story
type helps you to
discover more
details
Recurring events
contain a when
detail with an every
preposition
If an event has at
least one
changeable when
detail it is evolving
After you have identified all the when details and documented them with example
data, you use this information to determine the story type which in turn will give
you strong clues about subsequent detail types you can expect especially the how
many details.
Recurring Event
If the event contains a when detail with an every preposition and the example
stories confirms that it occurs on a regular periodic basis then the event is recur-
ring. If so, it will often contain balance measures. You should check for these when
you ask your how many questions.
Evolving Event
If you have two or more when details you may have an evolving event. If any of the
when details are initially unknown and/or can change after the event has been
created (and loaded into the data warehouse) then it is definitely an evolving event.
If so, you should look out for changeable duration measures that make use of the
multiple whens.
If an event is evolving you should ask the stakeholders for example stories that
illustrate the initial and final states—the emptiest event story possible, and a fully
completed one—to help explain how the event evolves.
Imagine for a moment that the stakeholders had responded to your additional
when question with:
Orders are delivered on delivery date and paid on payment date.
This would make the event evolving if the actual delivery dates and payment dates
are unknown when orders are loaded into the data warehouse.
Evolving events
contain additional
verbs that may be
modeled as discrete
events in their own
right
Notice that the “on” prepositions for these when details are preceded with the verbs
“deliver” and “pay”. These verbs are events in their own right that occur some time
after the initial order event. However, if stakeholders respond in this way they view
them primarily as order event milestones. Therefore, you should continue to
model them as when details of an evolving order event but you may also want to
model delivery and payment as separate discrete events too: You would ask “Who
delivers what?” and “Who pays what?” to discover if there are important details
that will be lost if deliveries and payments are only available at the order level.
If stakeholders provide multiple when details, pay attention to the verbs used in
prepositional phrases. The multiple verbs can identify a process sequence of
related milestone events. These events can be modeled as part of the current
evolving event and as discrete events in their own right if you suspect they have
more details. See Chapters 4 and 8 for more details on modeling evolving events.