Abstract: The rapid development of the network makes online news become an important source of acquiring information. It has a significant impact on the usability of Web sites whether the information published on the Web sites can reflect the current focus of attention or whether the latest progress of the event on the Web sites can be timely updated. In this paper, the clue development trend on the same subject related to the information on Web sites was obtained from the topic clue sentences identified by Conditional Random Field (CRF) model. The time range of topic clues can be inferred by clue development trends obtained, and further the effective range of Web information is estimated. On this basis, combined with the timeliness the information is published and the freshness of the content on Web sites, the timeliness of Web information can be evaluated reasonably. The experimental results show that the proposed method has a good effect on the timeliness evaluation of information on Web sites.

Key words: topic clue, timeliness, publication timeliness, content freshness, effective range

摘要： 网络的快速发展使得在线新闻媒体成为人们获取信息的重要来源。Web站点发布的信息是否能够反映当前关注的热点，是否能够及时发布事件的最新进展情况，对Web站点的可用性有重大影响。在利用条件随机场（CRF）模型识别主题线索句的基础上，得到与Web信息相关的同一主题的线索发展趋势。通过获得的线索发展趋势来推断主题线索的时间区间，进而估计出Web信息的有效区间，在此基础上结合时效性所包含的发布及时性和内容新鲜性两个方面来对Web信息时效性进行合理的评价。实验结果表明，所提方法在Web信息时效性评价上有较好的效果。

关键词: 主题线索, 时效性, 发布及时性, 内容新鲜性, 有效区间