Add robustness principle

Author: iluwatar

README.md

@@ -23,6 +23,7 @@ The list was inspired by [The Principles of Good Programming](http://www.artima.
 * [Law of Demeter](#law-of-demeter)
 * [Composition Over Inheritance](#composition-over-inheritance)
 * [Orthogonality](#orthogonality)
+* [Robustness Principle](#robustness-principle)
 
 ### Module/Class
 
@@ -250,6 +251,25 @@ Source: [Be Orthogonal](http://www.artima.com/intv/dry3.html)
 
 Source: [Orthogonality](http://en.wikipedia.org/wiki/Orthogonality_(programming))
 
+## Robustness Principle
+
+> Be conservative in what you do, be liberal in what you accept from others
+
+Collaborating services depend on each others interfaces. Often the interfaces need to evolve causing the other end to receive unspecified data. A naive implementation refuses to collaborate if the received data does not strictly follow the specification. A more sophisticated implementation will still work ignoring the data it does not recognize.
+
+Why
+
+* In order to be able to evolve services you need to ensure that a provider can make changes to support new demands while causing minimal breakage to their existing clients.
+
+How
+
+* Code that sends commands or data to other machines (or to other programs on the same machine) should conform completely to the specifications, but code that receives input should accept non-conformant input as long as the meaning is clear.
+
+Resources
+
+* [Robustness Principle in Wikipedia](https://en.wikipedia.org/wiki/Robustness_principle)
+* [Tolerant Reader](http://martinfowler.com/bliki/TolerantReader.html)
+
 ## Maximise Cohesion
 
 Cohesion of a single module/component is the degree to which its responsibilities form a meaningful unit; higher cohesion is better.

index.md

@@ -30,12 +30,13 @@ The list was inspired by [The Principles of Good Programming](http://www.artima.
 * [Law of Demeter](#law-of-demeter)
 * [Composition Over Inheritance](#composition-over-inheritance)
 * [Orthogonality](#orthogonality)
+* [Robustness Principle](#robustness-principle)
 
 ### Module/Class
 
 * [Maximise Cohesion](#maximise-cohesion)
 * [Liskov Substitution Principle](#liskov-substitution-principle)
-* [Open/Closed Principle](#open-closed-principle)
+* [Open/Closed Principle](#openclosed-principle)
 * [Single Responsibility Principle](#single-responsibility-principle)
 * [Hide Implementation Details](#hide-implementation-details)
 * [Curly's Law](#curlys-law)
@@ -257,6 +258,25 @@ Source: [Be Orthogonal](http://www.artima.com/intv/dry3.html)
 
 Source: [Orthogonality](http://en.wikipedia.org/wiki/Orthogonality_(programming))
 
+## Robustness Principle
+
+> Be conservative in what you do, be liberal in what you accept from others
+
+Collaborating services depend on each others interfaces. Often the interfaces need to evolve causing the other end to receive unspecified data. A naive implementation refuses to collaborate if the received data does not strictly follow the specification. A more sophisticated implementation will still work ignoring the data it does not recognize.
+
+Why
+
+* In order to be able to evolve services you need to ensure that a provider can make changes to support new demands while causing minimal breakage to their existing clients.
+
+How
+
+* Code that sends commands or data to other machines (or to other programs on the same machine) should conform completely to the specifications, but code that receives input should accept non-conformant input as long as the meaning is clear.
+
+Resources
+
+* [Robustness Principle in Wikipedia](https://en.wikipedia.org/wiki/Robustness_principle)
+* [Tolerant Reader](http://martinfowler.com/bliki/TolerantReader.html)
+
 ## Maximise Cohesion
 
 Cohesion of a single module/component is the degree to which its responsibilities form a meaningful unit; higher cohesion is better.