AppStream Architecture
Appstream is split into four logical blocks, on three principal levels.
Contents
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
- 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
- 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