There are two components of data when it comes to people and jobs. One is general (or should we call it demographic) information such as email, location, job titles, degrees, past companies and such. Then there is this skills information like functional/technical skills, soft skills, knowledge, domain experience, and others.
The former, from a data perspective, is easy to capture and analyse. The general information is clean, has patterns (emails for example), consists of discrete elements, and is quantitative (years of experience for instance). However, the latter i.e. the skills information suffer from lack of these. This information is fuzzy, subjective, unclear, lacks a pattern and consists of non-discrete elements. Because of this, expression of these is tough and difficult to analyze.