Josh On Design

Software Libraries are good. They allow abstraction and encapsulation; which encourages reuse. They also allow the library to be written by one person and used by another. This is reuse at the programmer level, not just the system level. A library can be written by a person who has domain expertise but used by someone else who has less or no expertise in that domain. For example: an XML parser. The implementer knows the XML spec inside and out, but the user of the lib needs only a basic understanding of XML in order to use the lib.