Often, algorithms have different requirement. Some will need to iterate all the vertices while other need to access the out-edges, etc. The subset of functionalities that each algorithm requires is often identified as a graph concept:

• A graph concept defines the functionality required by a family of algorithms.

As functionality always comes with a price (there’s no free lunch), it is important to have a fine grained structure of graph concepts that let the algorithm writer pick just what he needs and no more. In C#, a graph concept translates naturally and elegantly to interfaces. Therefore in the following, we will use interface or concept without distinction.

There are two main families of graph concepts in FastGraph:

• Traversal Concepts
• Mutation Concepts

Graph concepts have been introduced by the Boost Graph Library authors and the design of FastGraph follows their design.