The RSS 2.0 specification allows adding information in RSS feeds, in a simple way: just add XML nodes with a namespace.

This extension possibility is used in Erssical to handle additional information relative to events, initially to share software developer events. This additional information consists in:

• the link to the event information,
• the intended audience (a string),
• the type of event (conference, course, ...),
• some keywords (a list of strings),
• the speakers (a list of strings),
• the organizers (a list of strings),
• the start date and hour,
• the end date and hour,
• the "level" of the audience (beginner, confirmed, expert, ...).

All fields are optional. The details of the XML representation of this information are given on Events.

A query is composed of:

• a mime-type specifying what to output,
• a list of source RSS channels,
• an optional target channel,
• an optional filter,
• an optional template.

A query is described in XML. An example of query is available here.

The details of the XML representation of a query are given on Queries.

When given a query, Erssical performs the following operations:

1. Fetch the source RSS channels given with a URL (as source channels can also be embedded in the query); each fetched channel can have default event information specified; in this case, the event information of each item of the channel is merged with the default information. For example, default keywords are added to all items of a channel.
2. Merge the items of all source channels into a new channel. Description (title, description, image, ...) of this new channel is the same as the first source channel, except if a target channel was specified in the query.
3. If a filter was specified, only the items of this new channel matching the filter are kept.
4. Depending of the output format specified, output:
   • the resulting RSS channel,
   • the calendar data in Ical format,
   • or the XML tree obtained from the XML template provided in the query.

Erssical comes with a command line tool, erssical, and a HTTP server, erssical-server.

The command line tool will typically be used when generating static contents for your web site, while the HTTP server will be useful to dynamically merge information to embed in a web page. See Erssical command line tool and Erssical HTTP server for more information.