ZAP's Computing Services manages a large number of computing machines. This includes mainframes connected to over 200 personal computers and over 100 printers. Also, Computing Services manages and maintains network routers and connections, as well as many other machines the university staff have at home (laptops, PDAs, PCs, scanners, printers, wireless routers, etc.). When users at the university encounter problems with hardware or software applications, they call the IT Helpdesk's (a section of the university's Computing Services) technical support staff for assistance. The current system is manual and paper driven. The Helpdesk staff record the name, employee e-mail, department, and phone number of every user calling in with a problem. They also maintain a "problem log". A technician (called the "resolver") is assigned to every problem in the problem log. The Helpdesk staff record the name, employee e-mail, office location, and phone number of each resolver. For each problem, the Helpdesk staff track the user reporting the problem, the resolver assigned to the problem, the date and time the problem was reported, and a brief description of the problem. A problem may be of three kinds: {em online} for online jobs, {em batch} for batch jobs, and {em hardware} for hardware jobs. For batch jobs, it is also important to record the batch job name and number. For hardware jobs, it is necessary to record equipment number, type, and location. Each problem reported by a distinct user is assigned a unique problem number (even if different users call in to report the same problem). 
a- Draw a class diagram that accurately reflects the system's requirements. 
b- Write the ODL definition of three of your classes and their relationships.