Component based software engineering

I have a dream...

I have a dream...

Definition

CBSE emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a given software system. It is a reuse-based approach to defining, implementing and composing loosely coupled independent components into systems.

What is a component?

A piece of software that is connected to other only through its interfaces. 

An "interface" is an element that exposes a communication channel with a known contract

Development roles

• System architect (defines the requirements)

• Component designer (implements components)

• System integrator (composes components)

Communication Pattern: request-reply

• A server port provides an interface.
• 0-to-N clients send requests to server.
• The only purpose of the server is to provide answers (replies) as quickly as possible.
• Request can be either synchronous (wait for an answer) or asynchronous (don't wait, poll).
• Server must NOT make any assumption about clients. 

Communication Pattern: publish-subscribe

• A publisher exposes data (the topic).
• 0-to-N subscribers notifies that they want to receive the data.
• Publisher must NOT make any assumption about subscribers. 
• The interface is always asynchronous for the publisher and might be either SYNC or ASYNC for the subscriber.

Good components have:

• Strongly typed interfaces
• Explicitly documented contracts
• As little state as possible
• A well defined functionality
• An implementation that allow deployment to be configured by the integrator.

ROS doesn't enforce any of this

Coming next...

"Separation of concerns"