ことになっている is an alternation of ことになる, a grammar point showing that something has been decided by someone other than the speaker. It is a combination of the nominalizing use of こと (for creating noun-phrases), and the ている-form of the う-Verb なる ‘to become’. The primary difference between ことになる and ことになっている is that the latter focuses more on that something is ‘expected to (A)’, or ‘scheduled to (A)’. In other words, it is ‘becoming that (A)’, but has not actually happened yet.
This structure is often used after either the る or ない versions of verbs, in order to highlight the action which either is not not ‘expected’, or ‘scheduled’ to occur. Let’s take a look at the ‘scheduled to’ meaning first.

• 授業（じゅぎょう）は12時（じ）から始（はじ）まることになっています。
  The class is scheduled to start at 12.
• 社長（しゃちょう）は来週（らいしゅう）の飲（の）み会（かい）に参加（さんか）しないことになっています。
  The president is scheduled to not come to the party next week.

When indicating that something is ‘expected to (A)’, this is an example of ている’s use for expressing habitual or ongoing actions/states that reoccur under some specific set conditions.

• タクシーは左（ひだり）から乗（の）ることになっている。
  It is expected for customers to get into the cab from the left side.
• 生徒（せいと）たちは授業中（じゅぎょうちゅう）に教室（きょうしつ）を出（で）れないことになっている。
  Students are expected to not leave the classroom during class.