Conversation threading is a feature used by many email clients, bulletin boards, newsgroups, and Internet forums in which the software aids the user by visually grouping messages with their replies. These groups are called a conversation, topic thread, or simply a thread. A discussion forum, e-mail client or news client is said to have a "conversation view", "threaded topics" or a "threaded mode" if messages can be grouped in this manner. An email thread is also sometimes called an email chain. Threads can be displayed in a variety of ways. Early messaging systems (and most modern email clients) will automatically include original message text in a reply, making each individual email into its own copy of the entire thread. Software may also arrange threads of messages within lists, such as an email inbox. These arrangements can be hierarchical or nested, arranging messages close to their replies in a tree, or they can be linear or flat, displaying all messages in chronological order regardless of reply relationships. Conversation threading as a form of interactive journalism became popular on Twitter from around 2016 onward, when authors such as Eric Garland and Seth Abramson began to post essays in real time, constructing them as a series of numbered tweets, each limited to 140 or 280 characters.
Mechanism Internet email clients compliant with the RFC 822 standard (and its successor RFC 5322) add a unique message identifier in the Message-ID: header field of each message, e.g.
Message-ID: <xNCx2XP2qgUc9Qd2uR99iHsiAaJfVoqj91ocj3tdWT@wikimedia.org>
If a user creates message B by replying to message A, the mail client will add the unique message ID of message A in form of the fields
In-Reply-To: <xNCx2XP2qgUc9Qd2uR99iHsiAaJfVoqj91ocj3tdWT@wikimedia.org> References: <xNCx2XP2qgUc9Qd2uR99iHsiAaJfVoqj91ocj3tdWT@wikimedia.org>
to the header of reply B. RFC 5322 defines the following algorithm for populating these fields:
The "In-Reply-To:" field will contain the contents of the "Message-ID:" field of the message to which this one is a reply (the "parent message"). If there is more than one parent message, then the "In-Reply-To:" field will contain the contents of all of the parents' "Message-ID:" fields. If there is no "Message-ID:" field in any of the parent messages, then the new message will have no "In- Reply-To:" field.
The "References:" field will contain the contents of the parent's "References:" field (if any) followed by the contents of the parent's "Message-ID:" field (if any). If the parent message does not contain a "References:" field but does have an "In-Reply-To:" field containing a single message identifier, then the "References:" field will contain the contents of the parent's "In-Reply-To:" field followed by the contents of the parent's "Message-ID:" field (if any). If the parent has none of the "References:", "In-Reply-To:", or "Message-ID:" fields, then the new message will have no "References:" field.
Modern email clients then can use the unique message identifiers found in the RFC 822 Message-ID, In-Reply-To: and References: fields of all received email headers to locate the parent and root message in the hierarchy, reconstruct the chain of reply-to actions that created them, and display them as a discussion tree. The purpose of the References: field is to enable reconstruction of the discussion tree even if some replies in it are missing.
Advantages
Elimination of turn-taking and time constraints Threaded discussions allow readers to quickly grasp the overall structure of a conversation, isolate specific points of conversations nested within the threads, and as a result, post new messages to extend discussions in any existing thread or sub-thread without time constraints. With linear threads on the other hand, once the topic shifts to a new point of discussion, users are: 1) less inclined to make posts to revisit and expand on earlier points of discussion in order to avoid fragmenting the linear conversation similar to what occurs with turn-taking in face-to-face conversations; and/or 2) obligated to make a motion to stay on topic or move to change the topic of discussion. Given this advantage, threaded discussion is most useful for facilitating extended conversations or debates involving complex multi-step tasks (e.g., identify major premises → challenge veracity → share evidence → question accuracy, validity, or relevance of presented evidence) – as often found in newsgroups and complicated email chains – as opposed to simple single-step tasks (e.g., posting or share answers to a simple question).
Message targeting Email allows messages to be targeted at particular members of the audience by using the "To" and "CC" lines. However, some message systems do not have this option. As a result, it can be difficult to determine the intended recipient of a particular message. When messages are displayed hierarchically, it is easier to visually identify the author of the previous message.
Eliminating list clutter It can be difficult to process, analyze, evaluate, synthesize, and integrate important information when viewing large lists of messages. Grouping messages by thread makes the process of reviewing large numbers of messages in context to a given discussion topic more time efficient and with less mental effort, thus making more time and mental resources available to further extend and advance discussions within each individual topic/thread. In group forums, allowing users to reply to threads will reduce the number of new posts shown in the list. Some clients allow operations on entire threads of messages. For example, the text-based newsreader nn has a "kill" function which automatically deletes incoming messages based on the rules set up by the user matching the message's subject or author. This can dramatically reduce the number of messages one has to manually check and delete.
Real-time feedback When an author, usually a journalist, posts threads via Twitter, users are able to respond to each 140- or 280-character tweet in the thread, often before the author posts the next message. This allows the author the option of including the feedback as part of subsequent messages.
Disadvantages
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