Multi-label classification problem, which aims to assign multiple class labels to a given object, has recently attracted much attention. A single-label scenario, where each given object is associated with just one label, is rarely suitable for real applications, since real-world objects are usually associated with multiple labels. In text categorization, for instance, each document may belong to several topics or tags. For the purposes of this description, the terms document and electronic document may be used interchangeably. The main challenge associated with many real-world multi-label classification problems is to find the optimal mapping from the space of features to the space of label sets, which is particularly difficult since the potential set of labels that might be assigned to a given object is quite large (exponential to the total number of labels). There have been attempts to deal with this intrinsic complexity of finding the optimal mapping. These attempts, however, typically assume that the label space is relatively small and that at least some training data is available for each label.
One way of dealing with a multi-label classification problem is by treating it as a setting with independent binary classification instances, one for each possible label. This type of approach may be called a first-order approach. One potential problem with the first-order approaches is that their performance is usually non-satisfactory, as they operate on an assumption that the labels are independent of each other. Another limitation of the first-order approaches is that, as the number of labels increases, obtaining any significant amount of training data becomes increasingly expensive, making these first-order approaches non-scalable. Other approaches include second- and third-order approaches, which utilize correlations between different labels. Second-order approaches leverage pair-wise label relations. Third-order approaches leverage hierarchical or more complex label relations.
An on-line social network may be viewed as a platform to connect people in virtual space. An on-line social network may be a web-based platform, such as, e.g., a social networking web site, and may be accessed by a use via a web browser or via a mobile application provided on a mobile phone, a tablet, etc. An on-line social network may be a business-focused social network that is designed specifically for the business community, where registered members establish and document networks of people they know and trust professionally. Each registered member may be represented by a member profile. A member profile may be represented by one or more web pages, or a structured representation of the member's information in XML (Extensible Markup Language), JSON (JavaScript Object Notation) or similar format. A member's profile web page of a social networking web site may emphasize employment history and education of the associated member.