11 Daisy Implementation Intro

This section of the documentation is intended to guide you on your first trip through the deep and inner workings of Daisy. It is intended to show how it all fits together, which might not always be obvious by looking at individual source files.

This information is intended for people who want to hack on Daisy itself, not for those who simply want to use it.

11.1 Daisy Build System

The build system used by Daisy is Maven, an Apache project.

11.1.1 Maven intro

What follows is the very-very-quick Maven intro, for those not familiar with Maven.

Unlike Ant, where you tell how your code should be build, in Maven you simply tell what directory contains your code, and what the dependencies are (i.e. what other jars it depends on), and it will build your code. This information is stored in the project.xml files that you'll see across the Daisy source tree. There are a lot of them, since Daisy is actually composed of a whole lot of mini-projects, whereby some of these projects depend on one or more of the others.

An important concept of Maven is the repository, which is a repository of so-called artifacts, usually jar files. An artifact in the repository is identified uniquely by a group id and an id (both are simply descriptive names). Declaring the dependencies of a project is done by specifying repository references, thus for each dependency you specify the group id and id of the dependency. An example dependency declaration, as defined in a project.xml file:

    <dependency>
      <groupId>lucene</groupId>
      <artifactId>lucene</artifactId>
      <version>1.3</version>
    </dependency>

So where does the repository physically exist? Well, there can be many repositories. The most important public one is on ibiblio:

http://www.ibiblio.org/maven/

The repository is simply accessed using HTTP, so you can take your browser and surf to that URL. A repository like the one on ibiblio is called a remote repository. After initially downloading an artifact from the remote repository, it is installed in your local repository, which is by default located in ~/.maven/repository.

When you build a project, the result of the build is usually a jar file. Maven will install this jar file in your local repository, so that when you build another project that depends on this jar file, it can be found over there. When searching a dependency, Maven always checks the local repository first, and then goes off checking remote repositories. Which remote repositories are searched is of course configurable.

I should also tell you something about the build.properties and project.properties files. Both files contain properties for the build and configuration for Maven. The difference is that the project.properties files are committed to the source repository (SVN in Daisy's case), while the build.properties files are intended for local customisations (thus on your computer). So if you see something in a project.properties file that you'd like to change, don't change it over there (as this will otherwise show up as a modified file when doing svn status), but do it in the build.properties file. The build.properties file thus has a higher precedence than the project.properties file.

There is a lot more to tell about Maven, such as that it is actually composed of a whole lot of plugins, that there is something like "goals" to execute, that there is the possibility to have a maven.xml file to define custom goals with custom build instructions, and that all artifacts are also versioned. But I'll let you explore the Maven documentation to learn about that.