8.1: Introduction

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We say that Metacello is a package management system for Monticello. But what, exactly, does that mean? A package management system is a collection of tools that automate the process of installing, upgrading, configuring, and removing groups of software packages. Metacello groups packages to simplify things for the user and manages dependencies, i.e., which versions of what components should be loaded to make sure that the whole set of packages is coherent.

A package management system provides a consistent way to install packages. Package management systems are sometimes incorrectly referred to as installers. This can lead to confusion, because a package management system does a lot more than install software. You may have used package management systems in other contexts: examples include Envy (in VisualAge Smalltalk), Maven (in Java), and apt-get/aptitude (in Debian and Ubuntu).

One of the key features of a package management system is that it correctly loads any package: you should never need to manually install anything. To make this possible, each dependency, and the dependencies of the dependencies, and so on, must be specified in the description of the package, with enough information to allow the package management tools to load them in the correct order.

As an example of the power of Metacello, you can take a PharoCore image, and load any package of any project without any problems with dependencies. Of course, Metacello does not do magic: this only works as long as the package developers have properly defined the dependencies.