24 May 2008 acj   » (Journeyer)

This summer, I'm working on DebGraph (for Debian, as part of GSoC) with Robert Lemmen. Below is a brief description of where we're headed.

DebGraph is a tool that provides a simple, intuitive interface to the Debian package graph. The package graph contains information about packages (name, version, description, etc), their dependencies, and other useful details. By providing an easy way to interact with this graph, DebGraph enables useful analyses that can identify interesting or problematic constellations.

As an example, it is helpful for the Debian QA team to track cyclic dependencies (that is, packages that [in]directly depend on themselves). Such dependency cycles can be symptoms of package problems, and therefore it is important that there is tool support for locating and tracking them.

To date, many tools have been written to perform various tasks that involve analyzing Debian packages. The `lintian' tool performs tests on packages to ensure that they are complete. `Britney', another package analysis tool, assists the release and quality assurance teams by verifying package dependencies before promoting packages from the `unstable' distribution to `testing'.

As the number of packages in Debian has grown, the complexity of the package dependency graph has become difficult to manage. Development of new scripts that interact with package information involves addressing that complexity. This involves writing code that can represent the graph in memory and manipulate it, and such work is typically delicate and error-prone. It would be helpful to separate this functionality into a library that could provide generic graph infrastructure to anyone who needs to query or manipulate the Debian package dependency graph.

DebGraph aims to provide this generic infrastructure through a set of graph operators (e.g., union, intersection, find-cycles, and so on) that can be composed in complex ways to facilitate powerful analysis of the graph. In addition, the development of a functional query language will enable graph queries from domain-specific languages, thus removing the constraint of using C++ code to perform queries.

This work relieves developers of the burden of duplicating graph-specific code when developing new tools (or extending existing ones) that need access to the package dependency graph. By providing a generic infrastructure to support such tools, DebGraph enables tool developers (and others in the community) to focus on the issue at hand without becoming swamped with low-level details.

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