Demo: Entity maps

- [Instructor] There's one other artifact … that might be useful as you are working … from your entity map in the direction of the code. … The basic problem here is to put into a concise format … the jobs of the individual entities inside the system. … Now, again, this is something that I use index cards … or large post-it notes for. … So the basic idea here comes … from something called a CRC card. … CRC cards go back far in history. … They were developed by Kent Beck and Ward Cunningham … when they were teaching object-oriented design. … Rebecca Wirfs-Brock did a lot of work with CRC cards, … in fact, has written quite a nice book on the subject, … but this is from probably 20 years back now, … a long time ago. … The basic idea of the CRC card is to try and identify … the classes in the system, the responsibilities they have, … and the collaborators, who do they talk to? … Now, in an Envy model, … classes are not really going to be classes. … They're probably going to be services or something like that, …