Copyright Nancy Leveson, Sept. 1999 1980S: oo design: added inheritance, multiple inheritance, and polymorphism to ADT In process added complexity and increased some types of connectivity Lots of claimed advantages -- so far empirical evaluation is not supporting them well 1990s: Architecture Patterns Frameworks Kits etc
c Copyright Nancy Leveson, Sept. 1999 1980s: OO design: added inheritance, multiple inheritance, and polymorphism to ADT. In process added complexity and increased some types of connectivity. Lots of claimed advantages -- so far empirical evaluation is not supporting them well. 1990s: Architecture Patterns Frameworks Kits etc. �
Copyright Nancy Leveson, Sept 1999 Software Design Principles Design is a creative, problem-solving activity No recipe for doing it- always need some type of"magic Quality and expertise of designers is determinant for success Simon An expert has over 50,000 chunks of domain knowledge at hand Solving a problem involves mapping into knowledge available The larger this knowledge and the more accessible, the more successful the process will be
Copyright Nancy Leveson, Sept. 1999 Software Design Principles c Design is a creative, problem-solving activity. No recipe for doing it - always need some type of "magic". Quality and expertise of designers is determinant for success. Simon: An expert has over 50,000 chunks of domain knowledge at hand. Solving a problem involves mapping into knowledge available. The larger this knowledge and the more accessible, the more successful the process will be. �
Software Design Principles(2 Brooks, Curtis: Successful software development often depends on small number of exceptional designers who think on a system level Curtis: Such people might not be particularly good programmers Design problem: How to decompose system into parts each with a lower complexity than system as a whole while minimizing interaction between the parts such that the parts together solve the problem No universal way of doing this
c Copyright Nancy Leveson, Sept. 1999 Software Design Principles (2) Brooks, Curtis: Successful software development often depends on small number of exceptional designers who "think on a system level." Curtis: Such people might not be particularly good programmers. Design problem: How to decompose system into parts each with a lower complexity than system as a whole while minimizing interaction between the parts such that the parts together solve the problem. No universal way of doing this. �
Four Primary Design Principles Separation of concerns Deal with separate aspects of a problem separate 2. Abstraction Identify important aspects of a phenomenon and ignore details that are irrelevant at this stage Hierarchical abstraction build hierarchical layers of abstraction Procedural (functional)abstraction · Data abstraction Control abstraction(abstract from precise sequence of events handled, e.g., nondeterminacy)
Copyright Nancy Leveson, Sept. 1999 Four Primary Design Principles 1. Separation of concerns c Deal with separate aspects of a problem separate. 2. Abstraction Identify important aspects of a phenomenon and ignore details that are irrelevant at this stage. Hierarchical abstraction: build hierarchical layers of abstraction Procedural (functional) abstraction Data abstraction Control abstraction (abstract from precise sequence of events handled, e.g., nondeterminacy) �
Nancy Leveson, Sept 1999 Four Primary Design Principles(2 3. Simplicity Emphasis on software that is clear, simple, and therefore easy to check, understand, and modify 4. Restricted visibility Locality of information
c Copyright Nancy Leveson, Sept. 1999 Four Primary Design Principles (2) 3. Simplicity Emphasis on software that is clear, simple, and therefore easy to check, understand, and modify. 4. Restricted visibility Locality of information �