The Corpus functions

Now it is time to replace recent hardcoded values for the corpus with real functions, so open the evidence service and add the following modifications to it:

// src/app/evidence/evidence.service.ts 
//... 
@Injectable() 
export class EvidenceService { 
  private corpusSize; 
  private corpus: FirebaseListObservable <any>; 
  private IDFs: FirebaseListObservable <any>; 
  //... 
  constructor(http: Http, af: AngularFire) { 
    this.http = http; 
    this.angularFire = af; 
    this.corpus = af.database.list('Evidence/Corpus/Articles'); 
    this.IDFs = af.database.list('Evidence/Corpus/IDFs'); 
  } 
 
  corpusBuilder(keywords) { 
    // ToDo:  
    // 1. Fetch links for each keyword 
    // 2. Pass the link to EvidenceService for extracting contents 
    // 3. Save them under corpus key for further caluculation 
  } 
} 

Please notice that we have created two children under the Evidence/Corpus key. Apart from articles, we need to keep all IDF calculations somewhere...