a good partial key. Otherwise a composite attribute of all the weak entity’s attributes will be the partial key. Initial Conceptual Design for an Example Reality : Using a hypothetical example of an accounting system, as already stated above in Fig: . , following initial design based on ER Model concepts becomes the starting point of illustration.
Conceptual Design : According to the requirements listed in example reality, there exist five entities: Vouchers, Accounts, Employees, SupportDocuments and AccountsType· An entity type Vouchers with attributes Voucher No, Serial No, Voucher Date, Debit Account, Credit Account, Amount, Narration, authorised by, prepared by are used for storing accounting data of a transactions. Debit and amount are multi-valued attributes for debit vouchers and credit and amount are multi-valued for credit vouchers. Voucher No and Sno together constitutes the only key attribute of entity type vouchers. Therefore, it is specified to be unique.
A Conceptual entity type Accounts with attributes Code, Name and Type is used for keeping and maintaining a record of all accounts. Both Code and Name qualify to be the key attributes because of being specified as unique. An Entity Type Employee with attributes Employee ID (EmpId), Name, Address, Phone, ID of immediate boss (SuperId) is used to maintain records of employees in the organisation. Name is a composite attribute with its simple attributes as: First Name (Fname), Middle Initial (Minit) and Last Name (Lname).
The EmpId , specified to be unique, is the key attribute. SuperId indicates the EmpId of the controlling officer, the immediate boss. An entity type, Accounts Type with attributes CatId and Category is used to maintain records of various categories of accounts so that each of the accounts as stored in accounts entity are able to find their suitable place in financial accounting reports: profit and loss account and also the balance sheet. An entity type called Support with attributes Sno.
and Name is used to maintain records of all the support documents, which are annexed to the accounting voucher. Fig. . : Details of initial conceptual design based on example reality