• Every software system provides two different values to the stakeholders:
  • behavior
  • structure
• Software developers are responsible for ensuring that both those values remain high.
• Unfortunately, they often focus on one to the exclusion of the other. Even more unfortunately, they often focus on the lesser of the two values, leaving the software system eventually valueless.
• What programmers are
  • Programmers are hired to make machines behave in a way that makes or saves money for the stakeholders. We do this by helping the stakeholders develop a functional specification, or requirements document. Then we write the code that causes the stakeholder’s machines to satisfy those requirements
• must be developed by an organization with many teams
  • they have many concerns that require a Software Architecture that facilitates independent actions by those teams
    • this is done by seggregating the system into well-isolated, independently developable components
  • this way you can continue to add new use cases w/o interfering with old ones (Open-Close Principle)

Use cases

• The software in the use cases layer contains application-specific business rules. It encapsulates and implements all of the use cases of the system. These use cases orchestrate the flow of data to and from the entities, and direct those entities to use their Critical Business Rules to achieve the goals of the use case.

Entities

• Entities encapsulate enterprise-wide Critical Business Rules. An entity can be an object with methods, or it can be a set of data structures and functions. It doesn’t matter so long as the entities can be used by many different applications in the enterprise.