I would say the knot in the middle is the closed system structure at the processing phase. The input(s) is an open configuration structure as is the output phase.
Goal: post a reply
Think of a web page form with many data fields and submit button, or post and preview like this reply form. Anyone can visit, click buttons and type copious heaps of garbage in the data fields. Some of the inputs into the web server app are invisible from the end user perspective, or are default inputs that need not be part of the data entry for each submission. Your unique session ID and user name are part of this.
Receive data from user, filter any garbage, apply document formatting, write to database as archive for any future requests. Goal attained.
Send formatted web page back to original user indicating success. As with the left side, random stuff happens here on the right side of the bowtie knot, also an open configuration structure. Other users react or ignore, original poster sees an error then plans an edit, trolled moderator ragedeletes or yawns, etc.