title: What does actAs and relations mean in doctrine?
body: <p>I'm totally at a loss with the following schema.yml:</p>
  
  <pre><code>JobeetCategory:
    actAs: { Timestampable: ~ }
    columns:
      name: { type: string(255), notnull: true, unique: true }
  
  JobeetJob:
    actAs: { Timestampable: ~ }
    columns:
      category_id:  { type: integer, notnull: true }
      type:         { type: string(255) }
      company:      { type: string(255), notnull: true }
      logo:         { type: string(255) }
      url:          { type: string(255) }
      position:     { type: string(255), notnull: true }
      location:     { type: string(255), notnull: true }
      description:  { type: string(4000), notnull: true }
      how_to_apply: { type: string(4000), notnull: true }
      token:        { type: string(255), notnull: true, unique: true }
      is_public:    { type: boolean, notnull: true, default: 1 }
      is_activated: { type: boolean, notnull: true, default: 0 }
      email:        { type: string(255), notnull: true }
      expires_at:   { type: timestamp, notnull: true }
    relations:
      JobeetCategory: { onDelete: CASCADE, local: category_id, foreign: id, foreignAlias: JobeetJobs } 
  
  JobeetAffiliate:
    actAs: { Timestampable: ~ }
    columns:
      url:       { type: string(255), notnull: true }
      email:     { type: string(255), notnull: true, unique: true }
      token:     { type: string(255), notnull: true }
      is_active: { type: boolean, notnull: true, default: 0 }
    relations:
      JobeetCategories:
        class: JobeetCategory
        refClass: JobeetCategoryAffiliate
        local: affiliate_id
        foreign: category_id
        foreignAlias: JobeetAffiliates
  
  JobeetCategoryAffiliate:
    columns:
      category_id:  { type: integer, primary: true }
      affiliate_id: { type: integer, primary: true }
    relations:
      JobeetCategory:  { onDelete: CASCADE, local: category_id, foreign: id }
      JobeetAffiliate: { onDelete: CASCADE, local: affiliate_id, foreign: id }
  </code></pre>
  
  <p>And how to define it correctly?</p>