Tagging is a defining characteristic of Web 2.0. It allows users of social computing systems (e.g., question and answering (Q&A) sites) to use free terms to annotate content. However, is tagging really a free action? Existing work has shown that users can develop implicit consensus about what tags best describe the content in an online community. However, there has been no work studying the regularities in how users order tags during tagging. In this paper, we focus on the natural ordering of tags in domain-specific Q&A sites. We study tag sequences of millions of questions in four Q&A sites, i.e., CodeProject, SegmentFault, Biostars, and CareerCup. Our results show that users of these Q&A sites can develop implicit consensus about in which order they should assign tags to questions. We study the relationships between tags that can explain the emergence of natural ordering of tags. Our study opens the path to improve existing tag recommendation and Q&A site navigation by leveraging the natural ordering of tags.

标记是Web 2.0的定义特征。它允许社交计算系统（例如，问答（Q＆A）站点）的用户使用免费术语来注释内容。但是，标记确实是一种自由行动吗？现有工作表明，用户可以就哪种标签最能描述在线社区中的内容达成共识。但是，还没有研究用户在标记过程中如何订购标记的规律性的工作。在本文中，我们专注于特定领域问答站点中标签的自然排序。我们在CodeProject，SegmentFault，Biostars和CareerCup等四个Q＆A网站中研究了数百万个问题的标签序列。我们的结果表明，这些问答站点的用户可以就应为问题分配标签的顺序达成隐含共识。我们研究了标签之间的关系，这些关系可以解释标签自然排序的出现。我们的研究通过利用标签的自然顺序，为改善现有标签推荐和问答站点导航开辟了道路。