Domain-Driven Design: Tackling Complexity in the Heart of Software

Example
Yield Analysis Versus Booking

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Back to our trusty shipping example. A highly specialized team has been set up to analyze all the
bookings that flow through the firm, to see how to maximize income. Team members might find
that ships have empty space and might recommend more overbooking. They might find that the
ships are filling up with bulk freight early, forcing the company to turn away more lucrative
specialty cargoes. In that case they might recommend reserving space for these types of cargo or
raising prices on the bulk freight.
To do this analysis, they use their own complex models. For implementation, they use a data
warehouse with tools for building analytical models. And they need lots of information from the
Booking application.
From the start, it is clear that these are two 
BOUNDED CONTEXTS
, because they use different
implementation tools and, most important, different domain models. What should the relationship
between them be?
A 
SHARED KERNEL
might seem logical, because yield analysis is interested in a subset of the
Booking's model, and their own model has some overlapping concepts of cargos, prices, and so on.
But 
SHARED KERNEL
is difficult in a case where different implementation technologies are being
used. Besides, the modeling needs of the yield analysis team are quite specialized, and they
continuously play with their models and try alternative ones. They may well be better off
translating what they need from the Booking 
CONTEXT
into their own. (On the other hand, if they
can use a 
SHARED KERNEL
, their translation burden will be much lighter. They will still have to
reimplement the model and translate the data to the new implementation, but if the model is the
same, the transfer should be simple.)
The Booking application has no dependency on the yield analysis, because there is no intention of
automatically adjusting policies. Human specialists will make the decisions and convey them to the
needed people and systems. So we have an upstream/downstream relationship. What downstream
needs is this:
Some data not needed by any booking operation