The Coad Letter: Modeling and Design Edition, Issue 44, Strategies -- Boundary; Colors; Time Line; Status

By: Coad Letter Modeling Editor

Abstract: In this issue, we look at the origin of color modeling.

Dear Friend,

Exciting times on the project here in Singapore! We're busy building an object model and scenario views for consumer, commercial, and corporate lending (a surprisingly interesting problem domain ;-)

In fact, we've made very significant progress over the past two days. Strategy 97-1 was a major factor. Please read, consider, and apply. I think you will appreciate its impact.

We've added special colors to our model here (Strategy 97-2). A real improvement. I will use this new strategy again and again. I hope you will,

We're working in a domain where timelines are quite helpful (Strategy 97-3).

Strategy 97-4 is something we've encountered in several scenario walkthroughs. So I thought it might be a good one to pass along to you too.

Sincerely and with best wishes,

Peter Coad

PS. With special thanks to my friends and colleagues at United Overseas Bank.

Strategy 97-1 "Model Beyond the Boundary"

When someone sets or implies a system boundary, be sure to extend your model beyond the boundary. Here's why:
  • To understand context (must know a bit about what's outside, to effectively model what is inside).
  • To discover abstractions that apply within your system and within related systems. Wrap your model around those core abstractions.
  • To gain a different perspective, changing the way you view your own system (very much needed, especially when working with team members who have limited their thinking to fit within a defined system boundary for some time).
Here's what to look for:
  • Look for broader context. If it's a lending system, consider deposits and investments.
  • Look for what happens before and what happens next. If it's a credit line application system, consider prospecting for customers (before) and credit line implementation (after).

Strategy 97-2"Show Your Colors."

Build your models with color Post-It notes:
Color Meaning OM Book term
yellow party, role actor, participant 
pink moment, interval transaction
green thing specific item, place
blue description item

Use this pattern as a guide:

Post-It is a trademark of 3M.

[ Note: Later Party was changed to green and included in the Party,Place,Thing archetype - Steve 2/2001]

Strategy 97-3 "Use A Time Line to Select and Organize Moments and Intervals."

Develop a time line of significant things that happen in your domain. For example, in an application for a credit line, it's: opened, submitted, approved, selected, offered, accepted, implemented.

Which of these moments and intervals should you include in your model?
Follow these guidelines:

  • Group the ones that need just a date-time stamp; drop those date-time stamps into one class. Example: submitted, offered, accepted --> Application class, with attributes dateTimeSubmitted, dateTimeOffered, dateTimeAccepted.
  • Toss the ones your system has no responsibility for remembering. Example: selected.
  • Sequence the moment/interval classes left-to-right (people are used to seeing sequences that way). Then add object connections from one class to the next, and to the next.

Strategy 97-4 "Use Status Collections to End Repetitive Status Querying."

Rather than asking each member of a group what its status is, again and again, hold members in some status collections.

Example. Rather than ask each and every dividend object whether it is payable:

instead, a security object could simply hold collections of payable dividends and paid dividends, like so:

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