AppStream Architecture

Appstream is split into four logical blocks, on three principal levels.

Client

Software Center

• The existing Ubuntu Application Center fits the perceived need and is an established and stable project
  • Has CLA we might need to work around / fork.
  • Have to convert away from using custom social server to OCS, non-issue
  • Have to port to ?PackageKit 100%, non-issue
• Talks to zeitgeist for usage stats
• Has recommendations and featured applications
• Need the ability to tag applications and moderate comments

PackageKit

• http://www.packagekit.org
• Use the assumption that packages are an uninteresting implementation detail.
• Need to be able to search whilst we are installing, perhaps limited to existing xapian results.

xapian

• http://xapian.org/
• Established project used for many years to enable free text search using important things like priority and stemming that can return results in 10's of milliseconds.
• We discussed a relational database, but not suitable for our needs
• Need to rebuild every time we add/enable or disabled.

OCS

• http://www.freedesktop.org/wiki/Specifications/open-collaboration-services
• Provides a shared API we can add social media to an application installer
• Growing userbase and stable and approachable upstream
• Can have single server for all or private instance on own infrastructure with possible federation between distros

Mirror

Metadata

• Just another file on the mirror server: app-data.xml
• Contains data derived from the upstream desktop files and extracted at repo-compose time.
• Means we have different metadata for each repo
• Just another blob of data that can be downloaded by apt-get, yum, etc
  • See http://gitorious.org/appstream/resources/blobs/master/appdata.xml for an example, or schema here http://gitorious.org/appstream/resources/blobs/raw/master/appdata.xsd

Icons

• super-critical in search results
• app-data-32x32.tar.gz
• icons/32x32/foo.png
• Can encode location and type of icons in the appdata.xml

Compose server

• We explode the package files which contain a desktop file and extract the data from the desktop files
• All gets added to the app-data.xml and icons get (resized/converted?) and copied
• Probably a per-distro tool outputting shared format XML