MutiLabel classification
It is not super clear what is your main idea, but articles typically do have tags or categories and you may use that for the classification labels.
Humans are pretty good at articles tagging.
I have some 1000 news articles related to science and technology. I need to train a classifier which will predict say 3(computer science, electronics, electrical) confidence scores for each article. 
Each score represents how much the article belongs to each field.
The confidence score will be a value between zero and one.
But the data set doesn't have a training label.  
How do I proceed from here? What kind of data do I need?
How do I train such a model?