This post concerns itself with identifying the participants in our domain model that we have not classified as «moment-interval»s. That means we’ll look at «thing»s and their associated «description»s and «role»s. But first, I want to recap what we’ve completed so far over the past couple of days in case you’ve jumped in mid-series. If you’ve followed along, however, you can jump to the new stuff.

Work completed so far

The user stories

  • People join the club to become members and get invoiced monthly a flat fee and participation fees for classes
  • Participation fees for classes consist of a prorated amount of the instructor’s hourly rate and a percentage of the cost of the equipment used by participants in the class
  • Record member purchases of food and beverages from the club for rewards
  • For every ten dollars spent on food and beverages from the club, the member receives a one dollar credit on their next invoice.
  • Members RSVP for classes and their arrival is recorded
  • Instructors schedule rooms and equipment for classes

The identified concepts in our domain model by archetype

Moment-Interval (Pink)
Moment-Interval Detail (Pink)
Role (Yellow) Thing (Green) Description (Blue)
class
invoice
reward
member purchase
reservation
member arrival
membership
payment
member
instructor
person
room
equipment

The «moment-interval» “timeline”

In the last post, I worked on a draft design that took the moment intervals and laid them out in the flows that identify our business processes. The following figure shows that timeline.

Note that I have left off the archetype indicator «moment-interval» on the classes in the diagram. The fact that I colored the classes pink tells us that each of those classes have the «moment-interval» archetype.

«moment-interval» timeline for the atheletic club requirements

Domain-Neutral Components (DNCs) for the «moment-intervals»

To complete our domain model, we need to figure out the way in which the other classes participate in the «moment-interval»s identified and associated for our domain model.

I’ll walk through a couple of examples for how I would go about assigning the relationships. Then, I’ll just present a completed domain model for you to grok at your leisure.

I follow a simple methodology when completing the classes in a DNC:

  1. Identify the transactions in the system along their timelines
  2. Identify the participants of each of those transactions
  3. Determine roles needed to participate in the transactions
  4. Refactor common data to descriptions

The DNC for Membership

As with every exercise that involves using the Domain-Neutral Component, we start by identifying the «moment-interval» that acts as the nexus for the DNC.

membership dnc step 1

The first step we color modelers should take questions the need for «moment-interval detail»s in this DNC. As far as the requirements go, the Membership transaction has no collection of time-related details, so we can get rid of the placeholding pink box.

membership dnc step 2

Now, as color modelers, we should determine the «thing»s that participate in the transaction. Our thing list consists of Person, Room, and Equipment. Our requirement reads

People join the club to become members

Conspicuously missing from our list is the Club class. In software that would manage more than one club at a time, it would make sense to have a Club «thing». Because we have no such requirement, Club acts as an implied participant in every transaction.

Through a process of elimination of the available «thing»s, we conclude that the Membership «moment-interval» has Person as its only participant.

membership dnc step 3

Only «description» and «role» boxes remain. Starting with the «role», we ask, “Does the Person play a «role» in this transaction?” Reviewing the «role»s we’ve defined in this domain, «member» and «instructor», there’s really only one choice, eh?

membership dnc step 4

Finally, we have this concept of the «description». We must ask ourselves if we have different groups of Persons that participate in this system. For us, we have just people, not “rich people” and “poor people”, “smart people” or “Tea Party members” (I just lost some of my readership…), you know, categories of people. No. We don’t have those categories. Our system only deals with people as meat bags. So, we get rid of the «description» archetype placeholder and we arrive at the Membership DNC.

membership dnc step 5

The DNC for ProposedClass

Again, general DNC time for the ProposedClass «moment-interval». Note that the ProposedClass «moment-interval» has two types of «moment-interval-detail»s: EquipmentUsage and Reservation.

proposed class dnc step 1

Now, let’s look at the transaction ProposedClass and ask ourselves, “Who or what makes that transaction?” That’s a transaction between a Person acting as an Instructor and the club. As stated before, we don’t have a specific club class, so the «moment-interval» for ProposedClass should look like this.

proposed class dnc step 2

Next up, let’s look at the «moment-interval-detail» EquipmentUsage. We have a «thing» called Equipment in our list of identified nouns. Now, a «thing» should represent something specific in the world. No where in our requirements do we have to do inventory tracking for balls, racquets, mats, ropes, bean bags, and the like. So, we don’t have to track individual «thing»s. Rather, we just need to track collections of types of equipment. That means that I have a mistake in my initial categorization of nouns. :( So, let’s fix that.

Moment-Interval (Pink)
Moment-Interval Detail (Pink)
Role (Yellow) Thing (Green) Description (Blue)
class
invoice
reward
member purchase
reservation
member arrival
membership
payment
member
instructor
person
room
equipment
equipment

Due to that reclassification, Equipment participates in the transaction and doesn’t need a «role» because the Equipment doesn’t change the way that it participates in transactions. So, now we have this refined DNC.

proposed class dnc step 3

Finally, our requirement about Reservations reads

Members RSVP for classes

So, we fill in the «role» and «thing» appropriately, get rid of the «description», and we get this.

proposed class dnc step 3

Try the rest

Left as an exercise for you for the weekend, try filling out the DNCs for each of the remaining «moment-interval»s. I’ll post my design on Monday.

Have fun!