4. Many of the paradigms that we looked at involve middleware, a software module that serves as an intermediary among the participants of an application.

a. Consider the publish/subscribe message system model. How does the middleware in the paradigm allow publish/subscribe?

b. How might a middleware program allow cross-platform support?

c. How might a middleware program provide asynchronous interprocess communication?

d. Which of the paradigms involves middleware? Explain.