GBrowse Program Structure
This page gives a basic overview of how GBrowse has been organized and programmed, and is intended for developers to get a feel for the structure of the program so they can become more comfortable adding features to it or modifying it for their own needs. Help is always available via the mailing list, or on other sections of the GMOD wiki.
The backend is built as a series of modules in the Bio::Graphics::Browser2 package, it acts as a convenient, graphical, front-end to using the Bio::Graphics library. Bio::Graphics can load libraries of features on a genome and render images to display sections of the genome showing those features, but it can only be called via a Perl script or larger program. GBrowse automates the calling process and gives it a GUI so that more data (or a different section of the genome) can be requested by clicking a button. In addition to the backend, there is an optional database to hold named users & sessions, uploaded files, and sharing information.
The AJAX Pipeline
Most operations go through the gbrowse script, included in the cgi-bin. For each request, the script creates a new Browser2.pm object, opens the globals, then creates a new HTML.pm object and runs the run() function (inherited from Render). Render->run() is what controls the main page – it will send actions to Action.pm, rendering requests to HTML.pm, etc.
Render acts as a central hub for the program, it creates the objects which act as interfaces to the various parts of the program. UserTracks.pm controls the custom data the user can upload, Session.pm works with the current user's session, I18n.pm controls the internationalization, etc. All of these objects are initialized by Render.pm and can be accessed through it.
Some objects also need to be constructed outside of Render.pm; things like UserDB.pm, which deals with registered users, are called through another script, gbrowse_login, which doesn't go through the work of creating a whole new Render object.
The modules which make up GBrowse are contained in the lib directory in the SVN. They are as follows:
- Action (Bio::Graphics::Browser2::Action) - The Perl side of all AJAX requests. Each subroutine corresponds to the "action" parameter called in the AJAX request.
- AuthorizedFeatureFile (Bio::Graphics::Browser2::AuthorizedFeatureFile) - Adds HTTP authorization features to FeatureFiles.
- CachedTrack (Bio::Graphics::Browser2::CachedTrack) - Defines a Bio::Graphics::Browser2::Track option that manages the caching of track images and imagemaps.
- DataBase (Bio::Graphics::Browser2::DataBase) - Maintains a cache of database handles to improve performance on in-memory databases and other databases that have a relatively slow startup time.
- DataLoader (Bio::Graphics::Browser2::DataLoader) - An interface for managing files or URLs containing data and converting them into new databases for easier access. A full list of adaptors is available here.
- bam (Bio::Graphics::Browser2::DataLoader::bam) - A loader for the BAM half of the SAM/BAM file format.
- bed (Bio::Graphics::Browser2::DataLoader::bed) - A loader for the BED file format.
- bigwig (Bio::Graphics::Browser2::DataLoader::bigwig) - A loader for the BigWig file format
- featurefile (Bio::Graphics::Browser2::DataLoader::featurefile) - A loader for Bio::Graphics Feature Files.
- generic (Bio::Graphics::Browser2::DataLoader::generic) - A generic loader module.
- gff (Bio::Graphics::Browser2::DataLoader::gff) - A loader for the GFF#GFF3 file format.
- gff3 (Bio::Graphics::Browser2::DataLoader::gff3) - A loader for the GFF3 file format.
- sam (Bio::Graphics::Browser2::DataLoader::sam) - A loader for the SAM half of the SAM/BAM file format.
- wiggle (Bio::Graphics::Browser2::DataLoader::wiggle) - A loader for the Wiggle file format.
- DataSource (Bio::Graphics::Browser2::DataSource) - An interface for managing a data source, since GBrowse can work with a few (see the "Data Sources" drop-down menu on the main page)
- ExternalData (Bio::Graphics::Browser2::ExternalData) - A collection of utilities for working with non-FeatureFile data sets.
- GFFhelper (Bio::Graphics::Browser2::GFFhelper) - A helper module so plugins can handle GFF files more easily.
- I18n (Bio::Graphics::Browser2::Il8n) - Controls GBrowse's internationalization settings
- Markup (Bio::Graphics::Browser2::Markup) - Marks up a string with HTML cascading stylesheet styles in such a way that intersecting regions contain the union of the two intersecting styles.
- OptionPick (Bio::Graphics::Browser2::OptionPick) - An object to choose colour options (for tracks?)
- PadAlignment (Bio::Graphics::Browser2::PadAlignment) - A module to print out aligned raw sequence files in a padded, easily-readable format.
- Plugin (Bio::Graphics::Browser2::Plugin) - A base class for plugins.
- PluginSet (Bio::Graphics::Browser2::PluginSet) - Describes the API for using plugins.
- Realign (Bio::Graphics::Browser2::Realign) - A module to perform Smith-Waterman alignments on sequence data.
- Region (Bio::Graphics::Browser2::Region) - A module to enabe easy fetching/manipulation of regions.
- RegionSearch (Bio::Graphics::Browser2::RegionSearch) - A module to search through multiple databases for feature matches.
- RemoteSet (Bio::Graphics::Browser2::RemoteSet) - An API for handling a set of remote annotation sources
- Render (Bio::Graphics::Browser2::Render) - An interface to any non-HTML rendering code.
- HTML (Bio::Graphics::Browser2::Render::HTML) - Renders the HTML content and markup. Very important since GBrowse is HTML-based.
- RenderPanels (Bio::Graphics::Browser2::RenderPanels) - Interface for drawing and saving the panels which graphically show each track.
- Session (Bio::Graphics::Browser2::Session) - Controls the session and persistent variables.
- Shellwords (Bio::Graphics::Browser2::Shellwords) - A shell for Text::ParseWords::shellwords.
- SubtrackTable (Bio::Graphics::Browser2::SubtrackTable) - A module for creating an HTML table out of a track's subtracks.
- TrackDumper (Bio::Graphics::Browser2::TrackDumper) - A plugin to dump the data of a section of a track.
- UserDB (Bio::Graphics::Browser2::UserDB) - Manages all operations involving the user accounts database (both GBrowse users and users who use their OpenIDs to log in) and the uploads database.
- UserTracks (Bio::Graphics::Browser2::UserTracks) - Manages a user's uploaded tracks & files, permissions, etc.
- Database (Bio::Graphics::Browser2::UserTracks::Database) - A database-backed system for managing uploaded tracks & files.
- Filesystem (Bio::Graphics::Browser2::UserTracks::Filesystem) - A file system-backed system for managing uploaded tracks & files.
- Util (Bio::Graphics::Browser2::Util) - A library of generally useful utilities.
There are a few variables available internally which describe three levels of the current "state" of GBrowse. The are as follows:
Globals is a Browser2.pm object, and it loads information pertaining to the state of Gbrowse's setup on the computer it's running in from the Gbrowse.conf file and stores it in easily-accessible methods. It doesn't change between users or page reloads. A full description of what each setting does can be found at <configuration file page>.
Session is a Browser2::Session object, and it keeps user-specific information that is to be kept for every time the user logs in, such as the username, whether or not it's private, the plugin settings, and a copy of the state (as described below.)
The state or page settings object is the current “state” of the browser for the specific user – which tracks are on/off, added/removed, etc. It contains mainly user interface settings, things that would not heavily interfere with a user's experience if they couldn't be retrieved for whatever reason.