Watermark-Test  A global publishing company that publishes books and journals wants to develop a service to   watermark their documents. Book publications include topics in business, science and media. Journals   don’t include any specific topics. A document (books, journals) has a title, author and a watermark   property. An empty watermark property indicates that the document has not been watermarked yet.  The watermark service has to be asynchronous. For a given content document the service should   return a ticket, which can be used to poll the status of processing. If the watermarking is finished   the document can be retrieved with the ticket. The watermark of a book or a journal is identified   by setting the watermark property of the object. For a book the watermark includes the properties   content, title, author and topic. The journal watermark includes the content, title and author.   Examples for watermarks:  {content:”book”, title:”The Dark Code”, author:”Bruce Wayne”, topic:”Science”}  {content:”book”, title:”How to make money”, author:”Dr. Evil”, topic:”Business”}  {content:”journal”, title:”Journal of human flight routes”, author:”Clark Kent”}  a) Create an appropriate object-oriented model for the problem.  b) Implement the Watermark-Service, meeting the above conditions.  c) Provide Unit-Tests to ensure the functionality of the service.