irc-books/docs/services.dot

digraph Services {
   node [shape=rect];
   rankdir=LR;
   IRCClient
   FileFetcher
   BookUnpacker
   WebAPI
   DBCacheUpdater
   DB

   WebAPI -> IRCClient -> FileFetcher -> BookUnpacker
   FileFetcher -> DBCacheUpdater

   WebAPI -> DB[label="Search" style=dashed];
   DBCacheUpdater -> DB[label="Save cache" style=dashed];
}