Create an E-R diagram



Bob owns a small company called Bob’s Home repairs. He does the small home repair jobs that the large companies pass by. Need some wood work or wood furniture fixed? Call Bob.

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Here is how the business works:

Someone calls Bob and asks him to bid on a job. He drives over, looks at the situation, and gives them a bid. Sometimes it is an official looking bid by mail, and sometimes it is scribbled on notebook paper. He decides how long it will take to do the job (he bills by the hour), how much wood will be needed, any odds and ends that are unique to the job, and an overall price. He moves from job to job and bills customers as he finishes the work.

Bob buys items and supplies from a variety of places, but he buys stuff only when it is needed for a particular project. A potential problem: if he gets behind on his payments to various suppliers, then they won’t let him order any more. This would stop his business dead in its tracks. His biggest and most crucial supply is lumber (the price rises and falls constantly). So, he must pay all bills within 30 days of receiving them, especially the lumber companies.

Bob is pretty nice to his customers. They don’t have to pay until the work is completed and they are satisfied with his work. This has occasionally led to some problems because the cash coming in is sometimes slower than the cash going out, and he would like to have a better idea of when his bills are due and when his customers will be paying.

Currently, all business records are kept in Bob’s head and in one file cabinet. Sometimes he forgets which jobs he bid on and how much he bid on them. He doesn’t call potential customers to ask about earlier bids, but this could increase business. He wants reports on suppliers that need to be paid and customers that are slow in paying their bills. So, he wants to computerize these aspects of the business to make things more efficient. Can you help him?

Here is what you need to be able to provide Bob in order to land your first consulting contract:

  1. A list of all business rules involved and an E-R diagram (crow’s foot) of the situation.
  2. A script that will create the tables and enter a minimum of 3 sets of data for each table (more if necessary for orders, bids, etc.).
  3. Documentation of your analysis of Bob’s data needs
  4. Some sample queries with sample outputs for the reports that he wants.
  5. A nice business cover letter that summarizes this package as a prototype/proposal and details how your services will meet his business data needs.

Here is what you don’t need to do:

  • You don’t need to computerize the entire business, just the processes that Bob finds most bothersome.
  • You don’t need to create forms for data entry. This is something you would do if hired as a consultant.

An outstanding project will have the following characteristics, with lower grades for projects that lack these things:

  1. The E-R diagram clearly identifies the entities, relationships, and attributes.
  2. The tables are in third normal form, and you used good names for the tables and the fields.
  3. The sample data is useful in creating sample reports.
  4. The script works with Oracle using the the 10g XE interface.
  5. The script has comments to make it easy to edit later. (dash dash space )
  6. The sample queries that will show Bob how the database will be useful in meeting his data needs.
  7. The business cover letter looks professional. A potential customer would be more likely to hire you because of it.
  8. The entire package is organized in a Word document for easy viewing and editing, with diagrams and scripts copied into the Word document rather than stapled together from separate files.


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