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

Example
The SEMATECH CIM Framework
In a factory producing computer chips, groups (called 
lots
) of silicon wafers are moved from one
machine to another through hundreds of steps of processing until the microscopic circuitry being
printed and etched into them is complete. The factory needs software that can track each
individual lot, recording the exact processing that has been done to it, and then direct either
factory workers or automated equipment to take it to the next appropriate machine and apply the
next appropriate process. Such software is called a 
manufacturing execution system
(MES).
Hundreds of different machines from dozens of vendors are used, with carefully tailored recipes at
each step of the way. Developing MES software that could deal with such a complex mix was
daunting and prohibitively expensive. In response, an industry consortium, SEMATECH, developed
the CIM Framework.
The CIM Framework is big and complicated and has many aspects, but two are relevant here.
First, the framework defines abstract interfaces for the basic concepts of the semiconductor MES
domain—in other words, the 
CORE DOMAIN
in the form of an 
ABSTRACT CORE
. These interface
definitions include both behavior and semantics.
Figure 16.24. A highly simplified subset of the CIM interfaces, with
sample implementations
If a vendor produces a new machine, they have to develop a specialized implementation of the
Process Machine
interface. If they adhere to that interface, their machine-control component
should plug into any application based on the CIM Framework.
Having defined these interfaces, SEMATECH defined the rules by which they could interact in an
application. Any application based on the CIM Framework would have to implement a protocol that
hosted objects implementing some subset of those interfaces. If this protocol were implemented,
and the application strictly observed the abstract interfaces, then the application could count on
the promised services of those interfaces, regardless of implementation. The combination of those

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interfaces and the protocol for using them constitutes a tightly restrictive large-scale structure.